Avoiding Altitude Sickness: Complete Beginner’s Guide (2024)

This is the beginners guide to avoiding altitude sickness in 2024.

In this comprehensive guide, you will learn:

• Three simple rules that could save your life
• Myths about altitude sickness
• High altitude dos and don’ts
• Lots of practical tips to use right now

If you want to learn how to prevent altitude sickness and stay healthy on your travels at high altitude — from Tibet to Kilimanjaro to Colorado — you’ll love this guide.

Let’s get started.

Chapter 1: Altitude Sickness Basics

In this chapter we’ll give you the fundamentals of altitude sickness.

Through personal experience and research, we’ve learned how to feel MUCH better at high altitude on trips to Tibet. 

We’ll share with you the lessons we’ve learned along the way.

So you won’t need to repeat our mistakes, no matter where you are traveling.

It is important to note that we are not medical experts and all the information provided here is only for educational purposes and not to be taken as professional advice. For your safety, consult with your doctor before undertaking any course of action related to altitude sickness medication or treatment!

What is altitude sickness?

Altitude sickness is your body’s negative reaction to traveling too quickly to high altitudes. As you go higher — especially to locations over 8000 ft like Lhasa, Cuzco, Telluride, or the peak of Kilimanjaro  — the air becomes “thinner.” 

That means, because of the lower air pressure at higher elevations, there is less oxygen available in each breath you take.¹ 

Right away, your body begins to work to make the best use of the reduced oxygen available. 

It physically changes, in some fascinating ways, to begin to adapt to the lack of sufficient oxygen.

What is a normal reaction to high altitude?

In the first few days, you will breathe faster and deeper, to take in more oxygen, and your heart rate will increase. 

Your body will be going through a number of complex changes. 

To put the science as simply as possible:

Due to breathing faster and deeper, your body takes in more oxygen but loses carbon dioxide. The blood becomes abnormally alkaline.

The body now has to figure out how to restore its normal acid-base balance.

One way it does this is by suppressing breathing! This becomes especially apparent at night. (More on that later…)

Another way is by reducing alkalinity through urine. ² 

For an excellent breakdown of the many complex changes that happen in the first few days of normal acclimatization, see Inga Aksamit’s An Unofficial Acclimatization Guideline for JMT Hikers.

The bottom line?

Your body will be going through some significant changes when exposed to high altitude, and you will need to give it some time to sync up all the processes. 

Most of these changes happen in the first two days at higher altitudes, though for some people, it can take four days. 

During this time, you may very likely:

• Notice a feeling of breathlessness when you exert yourself at high altitude. 
• Experience a changed breathing pattern at night, called periodic breathing. In periodic breathing (also called PB or Cheyne Stokes breathing), the breath alternates between deep and shallow breathing. As a result, you may wake frequently and feel a lack of air. 
• Need to urinate more frequently. 
• Become dehydrated, as your urine output increases, and as you lose more fluids due to your increased breathing rate and the dry mountain air. (Note that if you exert yourself physically while acclimatizing and therefore perspire more, you will intensify the tendency to dehydration.)

The changes you experience may not feel great, but they are normal acclimatization. They don’t mean that you have altitude sickness. 

If you do not go higher, stay sufficiently hydrated, and do not physically overexert yourself, most people will slowly begin to feel more normal after 1-3 days. 

Everyone will experience the normal physiological changes at altitude. And many will experience the sometimes unpleasant effects of these changes.

But not everyone gets sick.

How to know when you have altitude sickness and not just a normal reaction to high altitude?

The first and mildest form of altitude sickness is called Acute Mountain Sickness (AMS).

AMS can develop anytime in the first 24 hours or so at sleeping altitudes above 6000 ft. Though it is uncommon to develop AMS below 8000 ft, it can affect some particularly sensitive individuals at lower altitudes.

The classic first symptom is a headache. 

When you have a headache plus any one of the following — nausea, dizziness, fatigue, loss of appetite, vomiting, weakness  — then you can assume you have AMS.

A lot of people compare the mild stages of altitude sickness to having the flu, or a hangover. Some people feel truly horrible, and some just feel sort of crappy. 

So what’s the big deal about getting AMS? And why should you not just power on if you have the symptoms?

Why you absolutely should not ignore mild altitude sickness

Developing the early stages of altitude sickness is a warning sign that you are not acclimatizing well. And you may be at a higher risk of two much more dangerous conditions: 

One is called HACE and harms your brain. 

The other is HAPE and harms your lungs.

Both are potentially fatal, and if unrecognized and untreated can kill you within a matter of hours. 

We don’t say this to scare you, but because we want you to know that AMS, if ignored, can lead to HACE. And that the conditions that produce AMS also can produce HAPE. 

Wilderness medicine expert Tod Schimelpfenig has reminded us that to be clear, you can get HAPE, and possibly HACE, without symptoms of AMS. However, it’s good to know that AMS is a heads up that your body is not acclimatizing normally and you need, at the very least, more time to adjust to altitude.

People who get seriously ill and die from altitude sickness almost always ignored the earlier, milder warning signs. 

No one needs to die from altitude sickness, and this guide is all about giving you simple tools to keep you on the safe and happy side!

Let’s start with a basic fact…

Individual responses to altitude vary a lot

It’s important to know that individual bodies can respond to high altitude quite differently.

Some people are naturally less susceptible to developing altitude sickness.

Those who do develop AMS, do so at varying altitudes. Some develop symptoms at 6,000 feet. Others can go thousands of feet higher before feeling anything. 

Therefore, remember that any stories you hear of strategies that work for one person tell you nothing about how you may react to altitude. 

It is REALLY important to understand this.

You and your friends or family may react completely differently at high altitude.

Yolanda and Lobsang, the authors of this article, have helped hundreds of people travel to Tibet, and we have heard so many different stories of how travelers have felt on arrival at the Tibetan Plateau.

Some people say that they feel absolutely fine. Others feel like they have a bad flu.

We ourselves have had very different experiences on different trips.

The bottom line is that you can’t rely on another person’s experience to tell you what might happen with your body at high altitude.

Here’s one important thing you should know…

The surprising truth of who is at risk of getting altitude sickness

Your risk of getting altitude sickness has nothing to do with your age or physical fitness. 

A 20-year old fitness-freak marathon runner has no less risk than a 60-year old couch potato.

That’s right. 

In fact, there is some anecdotal evidence that younger, fitter travelers may actually be at greater risk because of a tendency to think they can or should power through the initial symptoms.

The percentage of people who develop altitude sickness symptoms at high altitude is not known exactly, but here are some statistics of the percentage of travelers experiencing symptoms of altitude sickness:

• 43% of trekkers at Pheriche, Nepal (14,248 ft/ 4343 m)³
• 36.7% of tourists in Lhasa, Tibet (11,975 ft/ 3658 m ) ⁴
• 53% of trekkers at Pheriche, Nepal (a different study) ⁵

The major risk factors for altitude sickness are:

• Your rate of ascent to high altitude
• A prior history of altitude sickness
• Your genetic makeup

You have no control over your genes, but to avoid getting altitude sickness, you need to make a slow ascent a priority. Especially if you have previously experienced altitude sickness in the mountains. (More on that in Chapter 4.) 

But first, here’s a quick personal story of how we learned to feel MUCH better at high altitude on our trips to Tibet by following the basic rules we will share with you in this guide. 

A personal lesson learned about how to feel MUCH better at altitude 

Our own first experience with travel to high altitude in Tibet is a cautionary tale of exactly what NOT to do…

Trip One: Fast Ascent, No Meds, Feeling Wretched

On our joint first trip to Tibet, we (your authors, Yolanda and Lobsang)  knew nothing and we did everything that we should not do. Here’s a list of some of our mistakes:

• We flew from 1500 ft in Chengdu to Lhasa (~12,000 ft)
• We did not take altitude sickness medication
• Before we were fully acclimatized to Lhasa, we took a trip to Lake Namtso, which is 3500 ft higher. 

Generally speaking, we felt like hell for 2-3 days in Lhasa. Like we had a gnarly hangover or a mild flu. We slept horribly, had solid headaches all the time, mild nausea, and weakness. After we felt a bit better, we took off on a road trip to even higher altitude and slept at Lake Namtso, where we repeated feeling and sleeping crappy, for just one night, thankfully.

The ONLY thing we did right was that we rested, almost completely, those first 2-3 days in Lhasa. It’s when travelers don’t rest and insist on hiking or skiing when they have the first symptoms of altitude sickness, that they are at greatest risk of developing HACE or HAPE.

Trip Four: Slow Ascent, Meds, Feeling Great

Three trips to Tibet later, Yolanda had her systems down. With her friend Meg, she: 

• Flew to an intermediate elevation, the city of Xining, at 7500 ft, and slept there for two nights to begin to acclimatize.
• Chose to take a train rather than a flight for the remaining distance to Lhasa.
• Took acetazolamide (Diamox), altitude sickness medication, starting 24 hours before reaching high altitude 
• Did not plan any major activities the first days in Lhasa.
• Allowed 4-5 days in Lhasa before continuing the journey.
• On a road trip out of Lhasa, planned the journey in steps, to increase the sleeping elevation each night gradually.

The difference in how Yolanda felt from this trip and the last one was HUGE. At every step along the way, she and Meg felt good. There were no wasted days of laying around feeling sick. And even though we took it easy in Lhasa the first few days, we had a great time walking casually around.

You might be wondering:

What do I need to know and to do to feel healthy when I go to Lhasa, or Telluride, or Everest or Kilimanjaro? 

That’s what we’re going to cover in the rest of this guide.

But first, some simple rules from altitude experts… 

Chapter 2: Simple Rules that Could Save Your Life

If you remember nothing else from this post, let these rules be your guide when you go to high mountains.

The Golden Rules of Avoiding Altitude Sickness

1. If you feel unwell at altitude it is altitude illness until proven otherwise. 
2. Never ascend with symptoms of AMS.
3. If you are getting worse (or have HACE or HAPE), go down at once. 

— Originated by Dr. David Shlim at the CIWEC Clinic, Kathmandu

---

U.S. CDC Recommendations to Prevent Death or Severe Illness at Altitude

• Know the early symptoms of altitude illness, and be willing to acknowledge when they are present.
• Never ascend to sleep at a higher altitude when experiencing symptoms of altitude illness, no matter how minor they seem.
• Descend if the symptoms become worse while resting at the same altitude.

— United States’ Center for Disease Control Rules for Altitude:

How exactly can you know the early symptoms?

Read on…

Chapter 3: What Does Altitude Sickness Feel Like?

Now it’s time to get into the nitty gritty of high altitude sickness. 

Specifically, we are going to look at the symptoms of the three types of altitude sickness.

And in this chapter we are going to show you the warning signs to look for, in yourself and your companions.

Let’s dive right in.

How to recognize the early symptoms of altitude sickness

The first symptoms of altitude sickness usually begin 2-24 hours after you arrive at altitudes over 8000 ft/2500 m. (Particularly after the first night at a new altitude.)

(Though some people get altitude sickness as low as 6500 feet/2000 meters, it’s more common for those who are susceptible to start developing symptoms over 8000 ft.)

Again, the hallmark symptom is headache, though if you have a headache alone, this is not considered altitude sickness. Also, some people will have AMS without a headache, but with the other symptoms.

If you have a headache along with any of the following, you can assume you do have Acute Mountain Sickness (AMS):

• tiredness/weakness/fatigue
• light headedness or dizziness
• vomiting/nausea
• shortness of breath
• loss of appetite
• A general feeling of malaise

Generally speaking, you may feel like you have the flu, or an alcohol hangover. 

Having AMS in itself is not life-threatening. 

However, it is not “normal” to have a headache at altitude. If you do, you need to be willing to admit that you may have altitude sickness, and to respond with the appropriate actions. This is the first, critical, step to stay out of trouble.

While you are experiencing symptoms of altitude sickness, the most critical thing you should do is NOT GO ANY HIGHER. 

AMS symptoms normally begin to decrease after about three days, but in some rare cases, they progress to a more severe form of high altitude sickness. 

This is why it is important to look out for the development of further symptoms that might lead to High Altitude Cerebral Edema (HACE).

You’ll learn the signs and symptoms of HACE right now…

How to know when your brain is in trouble

“Cerebral,” of course, refers to the main part of your brain, the cerebrum. And “edema” is swelling caused by excess fluid in your tissues. 

When you have HACE, your brain swells, and stops functioning correctly. 

This is why victims of HACE display:

• Loss of physical coordination
• Act confused or disoriented
• May have a change of personality and may display, for example, uncharacteristic euphoria or depression
• May have slurred speech/garbled speech, or a loss of speech

They may appear drunk. And If the victim gets worse, he or she may exhibit:

• Hallucinations
• Drowsiness / semi-consciousness
• Coma

You should note that a person with HACE is confused and unable to think clearly. 

He or she will likely not understand that they are in danger. 

Also, as they lose physical coordination, they are at greater risk of falling.

HACE can be fatal within 48 hours or less if untreated. 

Warning Signs of HACE

The warning signs to look for, especially if the person has shown symptoms of AMS:

• Loss of coordination, which may manifest as an unsteady walk, or a staggering walk as if the person is drunk. To test the victim, have the person walk a straight line. Draw a straight line on the ground, and ask the victim to walk the line, with one foot in front of the other, heel to toe. If she or he cannot do this quite easily, you can assume the person has HACE.
• Disorientation or confusion

Other signs and symptoms that are not specific to HACE but that suggest AMS and may be part of the picture:

• Splitting headache that is not helped by medication (Note that you can have HACE without a headache, as well.)
• Nausea and vomiting (or an increase in nausea and vomiting)
• Increasing fatigue and weakness, and decreasing activity (The victim appears excessively tired, and is dragging behind everyone else.)
• Sleepiness
• Shortness of breath

HACE can be misdiagnosed as hypothermia, diabetes, or the consumption of excess alcohol or recreational drugs.  (Alternatively, one of these problems can be misdiagnosed as HACE.)

Before talking about the important topic of treatment of HACE, let’s look at another potentially fatal form of altitude sickness called HAPE.

How to know when your lungs are in trouble

High Altitude Pulmonary Edema, or HAPE, causes a dangerous accumulation of fluid in your lungs. 

Unlike HACE, it is not a more extreme form of AMS. Although people with HAPE also often have AMS, it is possible to have HAPE without any signs or symptoms of AMS.

A person with HAPE will have:

At least two of the following symptoms:

• Cough
• Difficulty breathing when at rest
• Chest tightness or congestion
• Weakness or decreased exercise performance

At least two of the following signs:

• Wheezing or crackles in at least one lung field
• Central cyanosis (Purple or bluish discoloration of the tongue, lips, and mouth, which is often accompanied with peripheral cyanosis, a blueness visible in the fingernail beds.)
• Tachycardia (abnormally fast heart rate)
• Tachypnea (abnormally fast breathing)

—According to the Lake Louis Consensus on the Definition of Altitude Sickness

Warning Signs of HAPE

Look for:

• Increasing breathlessness on exertion leading to shortness of breath even at rest 
• Cough, which possibly produces pink or frothy sputum 
• Extreme fatigue 
• Sounds of gurgling, rattling, wheezing, or crackling when breathing
• Fast, shallow breathing 
• Feelings of fullness, tightness, or congestion in the chest
• Gray, blue or purple lips or fingernails. 
• Drowsiness

HAPE often occurs 2-5 days after an ascent. ⁶

Importantly, HAPE can be confused with other respiratory conditions, like a high altitude cough, bronchitis, asthma, or pneumonia. 

HAPE can be fatal if untreated, and is the leading cause of death due to altitude sickness.  Like HACE, it can progress rapidly. 

That’s the bad news. 

The good news is that both HAPE and HACE can be preventable. 

The great majority of people who get HACE ignored the rule against descending to a lower elevation with symptoms of AMS. 

Similarly, the great majority of victims of both HACE and HAPE ignored the primary rules of altitude sickness prevention. 

With that, here’s how to avoid getting altitude sickness…

Chapter 4: How to Avoid Altitude Sickness

For the best chance to avoid getting sick or dying from altitude sickness, you need to take one simple step. 

Here it is:

#1: Ascend slowly

Your most effective way to prevent altitude sickness is incredibly simple. 

Ascend slowly.

It doesn’t matter how you ascend — flying, driving, hiking or climbing. If you increase your elevation too quickly, you are at high risk of getting sick.

AMS [Acute Mountain Sickness] is…highly correlated with speed of ascent…

— The incidence, importance, and prophylaxis of acute mountain sickness

There is no 100% sure way to avoid getting altitude sickness because each individual has a unique response to high altitude based on your physiology and genetics. 

HOWEVER, the great majority of us can reduce the risk of getting sick at high altitude by just giving our bodies time to adjust to the decreased oxygen. 

You can do this by taking your time to get to sleeping altitudes above 8000 ft/~2500 m. 

That means sleeping at intermediate elevations on the way up, to give your body time to acclimatize.

It’s how high you sleep that counts!

Have you ever heard the mountain climber’s mantra of “Climb high, sleep low?” 

In terms of getting altitude sickness, the altitude that you sleep at is more important than how high you go during the day. 

This is because sleeping at higher altitudes deprives your body of sufficient oxygen more than a day trip does. 

Why? 

As Dr. Roger Thompson notes on the APEX website: “During sleep at high altitude, the levels of carbon dioxide in the blood can drop very low and this can switch off the drive to breathe.”

As NOLS Wilderness Medicine Curriculum Director Tod Schimelpfenig⁷ notes, the point here is that we breathe better when awake and moving than when sleeping so we become more hypoxic at night. (Hypoxia is a condition in which the body’s tissues are deprived of an adequate oxygen supply.)

So you need to pay attention to the elevation at which you sleep and not as much to elevations you may climb to or visit during the day.

So how do I ascend slowly enough to stay healthy?

The general rules of thumb for ascending for the purpose of avoiding altitude sickness are:

• Allow at least two days to reach 9000 ft/~2700 m.
  • Plan to spend at least a night somewhere between ~6500 ft/ 2000 m and 9000 ft/~2700 m. 
  • Note that there is some evidence that sleeping at an elevation of 9,000 feet is more effective than lower elevations. 
• After you reach 9000 ft/ 2700 m, do not increase your sleeping altitude more than ~ 1500 ft/ 500 m per night.
• Spend an extra night at the same elevation every ~3000 ft/ ~1000 m. This means  that you would spend an extra night at the same elevation every 3 to 4 days.

#2: If you can’t ascend slowly, consult a doctor for Diamox

The absolute best way to prevent altitude sickness is to ascend slowly, but if that is not possible, you should consider asking a doctor about getting a prescription for Diamox, a medication used to prevent altitude sickness.

Diamox is the only altitude sickness medication that has been proven in peer-reviewed clinical trials to effectively prevent altitude sickness and help your body speed up the acclimatization process. (Unless you go too high, too fast.)

How Diamox works in your body

You may remember that as the body acclimates to high altitude, your blood becomes overly alkalinic. This imbalance in turn causes a problem for the body – suppressed breathing. 

Diamox enhances the body’s efforts to reduce alkalinity in the blood.

As the CIWEC Hospital notes, in Altitude Illness Advice for Trekkers, “Diamox blocks an enzyme in the kidney and makes the blood acidic which is interpreted by the brain as a signal to breathe more.”

Notes for taking Diamox

• The recommended dose for prevention for an adult is 125mg every twelve hours. Higher doses have been shown to be effective, but produce more frequent and/or worse side effects. Lower doses (62.5mg every twelve hours) have also been found effective in a small study, but are not yet recommended as further research is needed. ⁸
• Acetazolamide is typically taken starting 24 hours before you begin ascending to high elevations, and stopping either after reaching a high point and having begun descent, or, in the case when ascending to one elevation and remaining there, after 2-3 days at the high altitude.
• If you are severely allergic to sulfa drugs, you may be at risk for cross-sensitivity. Talk to your doctor about strategies for determining if you are allergic, or for alternatives. But note that but most people allergic to a sulfa antibiotic are not allergic to acetazolamide. A trial of Diamox under a doctor’s supervision should be done if there is a sulfa allergy history. Such trials often show it is ok to take Diamox.
• Note that Diamox can be used for both prevention and treatment of altitude sickness, though higher doses are used for treatment.

There are a number of myths about Diamox that we explore in the Myths section below.

Other prescription medicines for altitude sickness

There are a handful of other prescription medicines that are also used for altitude sickness prevention. 

These medications have more specialized uses and should be discussed with your doctor. 

• Dexamethasone: For prevention of AMS for those who may have an allergic reaction to acetazolamide. Dexamethasone does not speed acclimatization but can be used to treat symptoms. It may be used for treatment of AMS. 
• Nifedipine: For prevention of HAPE in people particularly susceptible to it.

If you are going to very high remote places, you might want to talk to your doctor about getting prescriptions for medications that treat HACE and/or HAPE. 

Some of the medications we listed are also used as treatment for existing altitude sickness, but we will not discuss that here as we are only focusing on prevention in this post. 

(For more about medications used for treatment of altitude sickness, see the “Medications” section of the US CDC page on altitude sickness.) 

What about Ibuprofen?

There has been a lot in the media on the effectiveness of ibuprofen for preventing altitude sickness. 

However, a major study by top altitude sickness experts published in February 2019 concluded that “ibuprofen was slightly inferior to acetazolamide for acute mountain sickness and should not be recommended over acetazolamide for rapid ascent.” ⁹  

Still, Dr. Peter Hackett, one of the authors of the 2019 study, has also noted that “it is non-prescription, safe and most folks know how to use it, and it is only slightly inferior to Diamox.” ¹⁰

The widely respected Wilderness Medical Society also prefers acetazolamide and dexamethasone to ibuprofen. They cite the above and other studies, and note that ibuprofen’s “efficacy and safety (eg, the risk of gastrointestinal bleeding or renal dysfunction) over longer periods of use at high altitude remain unclear.” ¹¹ 

What about natural remedies?

There are a number of homeopathic or herbal remedies that are popularly considered to be helpful for altitude sickness.

However, none of them have been clinically proven to effectively prevent altitude sickness. 

Some of them have shown promise in a few studies, but to date there is no reliable clinical evidence to support the use of:

• Coca leaves
• Gingko biloba
• Rhodiola
• Chinese herbals medicines such as Sheng nao kang pills,  Fufang yi hao pills, Shu li kang capsules, Xing nao jing injections, and Danhong injection. 

Although natural remedies are attractive to many travelers, we do not recommend them until more robust clinical data is available. 

If you don’t want to use Diamox, the preferred prevention tool would then be a slow ascent. 

Coca leaves

A good example of a popular natural remedy is coca leaves. Note this discussion in the preeminent Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness.

“Chewed coca leaves, coca tea, and other coca-derived products are commonly recommended for travelers in the Andes for prophylaxis, and anecdotal reports suggest they are now being used by trekkers in Asia and Africa for similar purposes. However, their utility in prevention of altitude illness has never been systematically studied, and they should not be substituted for other established preventive measures….”

Note: It has been reported that coca leaves may be drug testable as positive for cocaine.

Gingko Biloba

Another supplement is Ginkgo Biloba, which is popularly thought to be helpful in avoiding altitude sickness. 

However, the Wilderness Medical Society guidelines, notes that:

“Although several trials have demonstrated a benefit of Ginkgo in AMS prevention, several negative trials have also been published. This discrepancy may result from differences in the source and composition of the Ginkgo products. Acetazolamide is considered far superior prophylaxis for AMS prevention.” 

Chinese herbal medicines

Chinese herbal medicines are similarly untested. 

An evidence-based study, Chinese Herbal Medicine for Acute Mountain Sickness: A Systematic Review of Randomized Controlled Trials,  determined that: 

“No firm conclusion on the effectiveness and safety of Chinese herbal medicine for AMS can be made. More rigorous high-quality trials are required to generate a high level of evidence and to confirm the results.”

Given travelers’ high interest in more natural altitude sickness medicines, we hope that more studies will be undertaken to help provide evidence-based guidance. 

Until then, Diamox is considered the medicine of choice if you absolutely cannot ascend slowly.

We hope that it is clear to you that prevention is the best cure for altitude sickness. 

Still, it’s good to know the basic treatments if you or a companion does get sick.

Chapter 5: Treatment

As much as we urge you to take all the preventive steps, no guide to altitude sickness would be complete without a chapter on treatment. 

Here are the basics:

What to do if you have symptoms of Acute Mountain Sickness

Above all, it is important to take AMS seriously, even if “all” you’re feeling is a headache and a little nausea, for example. 

Even if you have just headache and one other AMS symptom, you can assume you have mild Acute Mountain Sickness. 

And what you do next will either keep you out of trouble, or put you at risk of developing much more serious symptoms.

You should:

• If your symptoms are mild, stay at the same elevation until your symptoms resolve. 
• Let your travel companions and guide know about your symptoms
• Watch yourself and others for early warning signs that the AMS has progressed, or for HACE or HAPE.
• If your symptoms are severe or worsen rapidly, descend to a lower elevation immediately.  
• You can also treat your headache with ibuprofen or acetaminophen, and your nausea with nausea medication such as ondansetron¹².

If available consider:

• Use supplemental oxygen (at a rate of 2 litres a minute and/or until oxygen saturation levels are above ~90%).
• Diamox, the prescription medicine used to prevent AMS, can also be used for treatment of AMS. (The US CDC article on High-Altitude Travel & Altitude Illness  recommends 250mg twice a day.) It is important to discuss this with your medical professional prior to your trip.

It sounds simple but you’d be surprised how many travelers develop mild AMS, and continue to ascend higher. 

One big issue is the desire to stay with one’s group.

Often, the sick person’s tour group is continuing on to the next town, which is at a higher elevation. 

Or, a traveler feels awkward about calling attention to their condition if the symptoms seem so mild. 

For whatever reason, travelers do it all the time.

By climbing or driving or flying higher with AMS symptoms, you put yourself  in considerable danger. 

As much as you may be reluctant to disrupt your group, you may end up making things worse for them if they have a seriously ill person to rescue vs. making routine arrangements for you to stay behind for a day or descend. 

It is not common for mild AMS symptoms to progress to life-threatening, but the great majority of people who develop High Altitude Cerebral Edema (HACE) ignored the rule against ascending with symptoms of AMS.

Once you have identified AMS in yourself or someone else, it is important to watch for the development of worsening symptoms, in which case you should descend without delay. 

It is especially important to look out for brain-related signs of symptoms of HACE.

What to do if someone has symptoms of HACE

If someone in your group shows any signs of confusion or a lack of physical coordination (or any of the other HACE symptoms, you must take immediate action.

Get the person to a lower elevation, ideally at least 2,000 – 4,000 ft / ~ 600 – 1,200 m. Even a few hundred ft (~ 100 m) may help. 

Don’t leave it until the victim’s condition worsens to the point to which she or he cannot walk at all. 

One issue with HACE is that it often happens, or at least begins, at night. 

This can be a real problem.

 If the traveler’s thought processes are negatively impacted by HACE in the night, she very well may not understand that she is in trouble. The problem may not be noticed until a companion notices odd behavior. 

Even if the problem is noticed right away, there are normally complications with descending to a lower altitude in the middle of the night.

And though it may be very challenging to deal with the situation, you can’t wait until morning since delay can be fatal. 

It is recommended to go down to the last point at which the traveler woke up feeling well, without symptoms of AMS. 

Additional Options:

• Oxygen
• The prescription medicine dexamethasone can be prescribed by a doctor for the emergency treatment of HACE in remote high altitude situations — but this is beyond the scope of this article written for beginners. ¹³
• Hyperbaric bags are used by mountaineering expeditions and mountain clinics to treat HACE. ¹⁴

What to do if someone has symptoms of HAPE

With or without the symptoms of AMS, a person at high altitude may develop signs or symptoms of HAPE, such as:

• difficulty breathing at rest
• a cough with pink sputum
• purple or blue discoloration of the mouth area or fingernails
• extreme fatigue. 
• See more symptoms of HAPE in Chapter 3 above.

It is critical to act immediately if anyone in your party has any of the symptoms of HAPE, which can be fatal even faster than HACE. 

Descend immediately, while the traveler is still mobile rather than waiting for severe symptoms that would force the victim to be carried. 

Physical exertion can worsen the problem in someone sick with HAPE, so it is important that they descend slowly and with physical assistance. 

Additional Options:

• Oxygen (Even 2-4 l/m flow rates can make a big difference.)
• The prescription medicine nifedipine can be used to treat HAPE — but again this is beyond the scope of this article written for lay beginners.¹⁵
• Hyperbaric bags are used by mountaineering expeditions and mountain clinics to treat HACE. ¹⁶

Generally speaking, the treatments available to any traveler for a milder form of AMS is to refrain from ascending further until the symptoms resolve, and for HAPE or HACE, to descend as soon as possible.  

In all cases you can treat headache with ibuprofen or acetaminophen, and nausea medication with something like ondansetron.

With that, let’s debunk some of the more popular altitude sickness myths.

Chapter 6: Mountain Sickness Myths

It is astonishing how much misinformation you will find about altitude sickness. Here’s the truth about a few of the more pervasive myths:

Myth: Diamox hides the symptoms of altitude sickness

False. Acetazolamide, the prescription drug sold as Diamox, does actually accelerate your body’s natural acclimatization processes. 

Myth: If you are young and physically fit, you don’t need to worry as much about getting altitude sickness

False. Age and physical fitness are generally not considered risk factors for getting altitude sickness. Actually, there is some evidence that the risk of altitude sickness may decrease over age 50. And there is plenty of anecdotal evidence that young, fit people tend may tend to over-exert and try to push through altitude sickness, which can lead to severe illness or death.

Myth: You should slam water at high altitude

False. Before we get to the myth, we want to say that it is critical to hydrate sufficiently at high altitude. You need to be drinking enough water that your urine is the color of straw or champagne. If your urine is yellow, you are dehydrated. If dark yellow, you are extremely dehydrated. It’s easy to get dehydrated at high altitude for various reasons, including the fact that when you breathe in the mountains, you are exhaling moist air and inhaling cold, dry air.

However, there is a persistent myth that you should drink huge amounts of water. You need enough, but not too much. Drinking too much water can actually be harmful, as it dilutes your electrolytes. This can cause a potentially serious condition called “hyponatremia.” 

Myth: You shouldn’t take a shower or bath at altitude for the first few days.

False. This has nothing to do with your risk for getting altitude sickness and seems to be a myth propagated by Chinese tour companies for Tibet. We have asked some (very good) Tibetan guides about this, and they also insisted that it is correct. There is zero scientific evidence for this claim.

Myth: If you stop taking Diamox, your symptoms will “rebound”

False. Stopping Diamox simply slows down the accelerated acclimatization that you benefit from with Diamox. If your symptoms recur, you can always re-start Diamox. 

Myth: If you have been to high altitude and not gotten AMS, you won’t get it on subsequent trips

False. A prior history of altitude sickness is the strongest risk factor for getting altitude sickness. However, not getting altitude sickness on one trip does not shield you from developing it on later trips. There are many stories of high-altitude climbers and guides who ascend multiple times before suddenly developing AMS. 

Chapter 7: Real-Life Stories and Videos from Travelers

Now it’s time for us to share with you some real-life examples of traveler’s experiences at high altitude. 

Our main goal here is to give you a sense of what real travelers’ experience at altitude, and how they self-report feeling.

Please note that the opinions expressed in these videos and stories are the posters’ own, and should not be taken as expert advice. 

#1: VIDEO: At altitude in Argentina

A young climber at high altitude cannot speak at all normally, even though he seems fairly oriented. (And appears to understand that he needs help, which is often not the case with HACE victims.) Fortunately, his buddies descend with him, so that a few hours later and a few thousand feet down he seems much better.

Altitude sickness expert Peter Hackett notes that it is unlikely that the climber actually has HACE. Rather, Dr. Hacket told us ¹⁷, he is showing what is called a focal neuro deficit. He is not disoriented or confused, not drowsy, and his coordination is okay. Rather, he is just having trouble with speech. Still, Dr. Hacket notes,  laypersons thinking he has HACE is OK, since they will get him down, give him oxygen etc. 

Video: Altitude Sickness — High Altitude Cerebral Edema (HACE)

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#2: VIDEO: At altitude in Nepal

Russell Hepton, The Trail Hunter vlogger, shares a day by day account of the effects of altitude sickness on his Lukla to EBC trek in Nepal. 

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#3: STORY: At altitude in Peru

Lauren Mazzo writes about getting altitude sickness at 14,300 ft on a trek in the Peruvian Andes

I Got Brutal Altitude Sickness While Trekking in Peru — But It Was Still the Best Trip of My Life

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#4: STORY: At altitude in Tanzania

Tim Moore describes his experience on the 5-day ascent of the highest mountain in Africa. Note that the rate of ascent on this climb was FAR faster than all recommendations, and why there is so much altitude illness on Kilimanjaro.

Kilimanjaro? Well, it nearly killed me

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#5: STORY: At altitude in Tibet

Annie Groer recounts how she and some of her companions were shocked to feel awful on a short trip to Lhasa, Tibet. Check out the stories of other travelers she shares a bit down in the article. 

On a trip to the Himalayas, I learned about altitude sickness the hard way

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#6: STORY: At altitude in Nepal

A trekker ends up at the hospital in Kathmandu after collapsing on the way to Dingboche from Tengboche. (Some minor misinformation here.)

Altitude Sickness — An Experience and a Lesson

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#7: VIDEO: At altitude in Nepal

Ryan Purvis talks about his experience in the Annapurna range of Nepal.

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#8: VIDEO: At altitude in Peru

You can see the progression of altitude sickness in Caro, from the Lots of Fresh Air blog, on her trek above 5000 m on the Huayhuash circuit in Peru, and fascinatingly, her recovery as she descends.

Play

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#9: VIDEO: At altitude in Tibet

Yolanda O’Bannon (co-author of this guide) and Meg Moser taped quick videos along the way of a 2017 journey to Mt. Kailash, and on the Ganden to Samye trek, to report on how they felt at altitudes on different days above 12,000 ft. 

Brief video from the top of the Dolma Pass to give you a sense of the breathing. It’s not easy to hear but the video pans to a small group of folks where Meg and our guide are helping a young Chinese woman who is dangerously ill on the pass. 

See the whole playlist here:

Video Playlist: How do you feel at high altitude in Tibet?

We recommend you check out “In Darchen, before beginning the Mount Kailash Trek,” and “Day 4 of Ganden to Samye Trek.”

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Chapter 8: High Altitude Dos and Don’ts

Now that we’ve looked at how to identify, prevent and treat mountain sickness, let’s quickly review what to do before and during your trip.

Before you go

DOS

• Plan a trip with a slow ascent.
  • Avoid going from low altitudes to over 9000 feet in a single day. Once you are above 9000 ft, avoid moving higher than 1600 ft a day, and take an extra day at the same altitude every 3300 ft/ 1,000 m.¹⁸
  • Many guide services offer trips with shorter or longer acclimatization periods. Avoid trips that don’t adhere to recommended ascent schedules. 
• If you have no choice but to make a rapid ascent, see a doctor about the possibility of taking altitude medication.
  • And start the medication 24 hours before reaching high altitude. ¹⁷ (Diamox begins to work quickly, so starting it 24 hours in advance is mostly to see if you tolerate the medication.)
• Know the symptoms of AMS, HACE and HAPE
• PLUS, use a knowledgeable guide
  • If going on a guided trip, use an agent or guide who can tell you specifically what training s/he has in relation to altitude sickness prevention and treatment. And how they handle altitude sickness on the trip.

Once you reach high altitude

DOS

• Look out for yourself and your companions.
  • Be prepared to stop if you or others exhibit symptoms of altitude sickness. Be prepared to go down if the symptoms worsen, even if it means not reaching your goal.
  • If you are hiking with a group of friends, discuss emergency scenarios ahead of time and agree on certain actions, especially not leaving anyone on their own. 
• Drink sufficient water
  • Enough so that your urine is the color of champagne or white wine.
• Stay warm.
  • It is often cold at high altitudes and you don’t want your body to be fighting a drop in body temperature at the same time it is trying to adjust to high altitude. 
• Consume enough calories for the level of exertion you are doing. There has long been a recommendation to eat plenty of carbs at high altitude, with the thought that carbs aid ventilation and efficient use of oxygen in your body. However, two of the altitude experts that we shared this document with commented that they think that the carb recommendation may be a myth, and that there is not good science to back it up. One notes that the impact of the metabolism of the carbs, which does take less oxygen than fat and protein do, may be overstated.

DON’TS

• Ascend with obvious altitude sickness symptoms.
• Take sedatives (like certain sleeping pills). Some sleeping pills are okay, according to this list created by altitude expert Peter Hackett and shared by another expert, Inga Aksamit.
• Overexert yourself in the first 24-48 hours. Mild to moderate activity, like walking, is recommended.
• Drink alcohol, which depresses breathing 
• Drink excessive water.
  • You need to drink enough, but if you over hydrate, you can cause a dangerous imbalance by diluting salt and other electrolytes. Drink enough so that your urine is champagne colored.

Chapter 9: Gold Standard Resources for Altitude Sickness Prevention

Now that you’ve mastered the basics of altitude sickness prevention, you may want to learn more. 

While learning about avoiding altitude sickness, we’ve explored A LOT of resources, and want to share with you a list of blue ribbon resources that we have found to be not only helpful and easy-to use but also authoritative and trustworthy.

Here they are:

Best of the Best

• Wilderness Medical Society’s Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness (2019 Update)
  • Definitive guide by an expert panel of wilderness medical professionals. Written for clinicians, but highly readable and recommended for interested lay people. 

User-Friendly Online Guides

• Apex  (Altitude Physiology Expeditions)
  • User-friendly info developed by medical students at the University of Edinburgh who take part in expeditions investigating the effect of altitude and hypoxia (low oxygen levels) on the human body.
• Institute for Altitude Medicine at Telluride
  • Nice, simple guidelines from expert Dr. Peter Hackett’s institute
• U.S. Center for Disease Control’s Yellowbook on Altitude Illness
  • Clear and comprehensive guide from expert doctors Peter Hackett and David Shlim.
• Altitude Acclimatization Facebook Group
  • Active Facebook group with excellent resources and discussions.
• An Unofficial Acclimatization Guideline for JMT Hikers 
  • Excellent resource developed by a hiker and two nurses.
• Outdoor Action Program Guide to High Altitude
  • User-friendly guide by Rick Curtis, director of the Princeton University Outdoor Action Program (This resource is good but has some outdated info.)
• British National Health Service on Altitude Sickness
  • Clear and easy to understand.
• Altitude Safety 101 
  • From the non-profit Center for Wilderness Safety
• Himalayan Rescue Association Nepal (HRA)
  • Nonprofit formed to reduce casualties in the Nepal Himalayas.

Video

Video Series by MedWild

Books

• Oxford Handbook of Expedition and Wilderness Medicine 
• [FREE] Travel at High Altitude: Free downloadable book in multiple languages by Medex
• Going Higher: Oxygen, Man, and Mountains

About the Authors

We, Yolanda O’Bannon and Lobsang Wangdu, had some up close and personal experience with altitude sickness on a trip to Tibet in 2002.

Never wishing to repeat that experience, we began to educate ourselves. Then, after opening YoWangdu Experience Tibet to help make Tibet travel more simple and ethical, we also became obsessed with helping Tibet travelers stay healthy at high altitude.

We’ve written extensively on preventing altitude sickness in Tibet, but lately we have seen a more general need to offer simple but evidence-based information to the general public.

With this guide, we hope to make it easy for new travelers to high altitude to stay healthy on their trips.

Special Thanks

Since we are not ourselves medical professionals or scientists, we asked a group of wilderness medicine experts to have a quick look at our guide.

We were, to be honest, amazed and honored by the quick, generous responses of this community of prominent, busy people obviously dedicated to helping people know and avoid the dangers of altitude sickness.

For their invaluable suggestions and contributions to the first draft of this text, we are extremely grateful to:

• Inga Aksamit, RN-BC,MBA
  • A registered nurse, winner of the Outdoor Writers Association of California’s Best Outdoor Book and an administrator for the excellent Altitude Acclimatization Facebook group.
• Peter Hackett, MD
  • Mountaineer, and world-renowned high altitude expert. Key author of the preeminent WMS guidelines for the treatment and prevention of altitude sickness.
• Chris Imray, PhD, FRCS, FRCP, FRGS
  • Mountaineer who has climbed the highest peak on each of the 7 continents, and vascular / renal transplant surgeon at University Hospitals Coventry and Warwickshire.
• Louis Reichardt, PhD
  • Prominent neuroscientist who is also the first American to summit both Everest and K2.
• Tod Schimelpfenig
  • Twice awarded the Warren Bowman award for contributions to wilderness medicine by a non-physician, and Curriculum Director for NOLS Wilderness Medicine.

We would like to emphasize that while the suggestions and contributions of the above experts significantly improved this guide, that all remaining mistakes are, obviously, our own.

Endnotes

Chapter 1

1. Note that the percentage of oxygen in the air remains constant at 21% no matter the elevation.
2. Volume Regulation and Renal Function at High Altitude across Gender
3. Oxygen at high altitude 
4. Acute mountain sickness among tourists visiting the high-altitude city of Lhasa at 3658 m above sea level: a cross-sectional study 
5. The incidence, importance, and prophylaxis of acute mountain sickness

Chapter 3

6. High Altitude Pulmonary Edema (HAPE)
7. Direct communication between Tod Schimelpfenig and the authors of this article. 

Chapter 4

8. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update
9. Altitude Sickness Prevention with Ibuprofen Relative to Acetazolamide
10.  Direct communication between Dr. Peter Hackett and the authors of this article.
11.  Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update

Chapter 5

12.  U.S. CDC article on High-Altitude Travel and Altitude Illness, written by Drs. Peter Hackett and David Shlim.  See Diagnosis and Treatment section.
13.  High-Altitude Travel and Altitude Illness (See Table 3-06)
14.  High-Altitude Travel and Altitude Illness. See Diagnosis and Treatment section.
15.  High-Altitude Travel and Altitude Illness (See Table 3-06)
16.  High-Altitude Travel and Altitude Illness. See Diagnosis and Treatment section.

Chapter 7

17.  Direct communication between Dr. Peter Hackett and the authors of this article.

Chapter 8

18. High-Altitude Travel and Altitude Illness (See Box 3-05)