High Altitude

How Much Do You Know About Altitude Safety?

So you’re going mountaineering, eh? Are you planning on skiing? How about climbing? Hiking? Overlanding? Maybe just chilling?

Mountain treks offer some the best recreation opportunities in the world, with clean air and beautiful vistas to boot. They also offer thin air with less oxygen. Altitude safety is paramount!

Enjoying the Fresh Mountain Air

Altitude Safety 101

One of the main health concerns when mountaineering are the effects of high altitude to a person. Different people have different reactions when exposed to it. Undoubtedly, this is due to several intervening variables. The major issues to watch out for include: altitude illnesses, hypothermia and frostbite, and even dehydration. There are many aspects of altitude safety that need to be addressed; which means, there’s far more than simply oxygen levels at altitude. Did you know for example, that many medications react differently or in a different speed than at sea level? Read on to Learn More!

Prevention First

Slow AscentAltitude Safety while Mountaineering

A Latin saying goes, “festina lente“, or “make haste slowly”. Like everything in life, it also applies when going up mountains, especially the higher ones. You must make your way to the mountaintop slowly. Doing otherwise can have serious, even fatal consequences. But high altitude illnesses like Acute Mountain Sickness can be prevented and its serious effects avoided—simply by ascending slowly.

The most important thing is to avoid AMS by acclimatizing properly by a gradual ascent. A recommended rate of ascent is to climb no more that 500 meters a day over an altitude of 3000 meters. In addition, you could also take a rest day every third day. If this is not possible, because of the position of the huts or campsites, you could also do staging, where you remain at an intermediate altitude between 3000 and 4000 meters for an extra day before ascending any further.

Also, always sleep at a lower altitude than the highest point reached that day. Sleeping at least 1,500 to 2,000 feet in elevation higher that the night before has been shown to help safely acclimate the body more than sleeping higher than that altitude gain.


Hydrate!  Hydrate!  Hydrate!

Although dehydration does not *cause* altitude sickness, it does decrease physical performance and the ability to generate heat. This will contribute to chilling and fatigue, which then could lead to altitude sickness, as well as hypothermia and frostbite. Drink at least 4 liters of water a day. Six liters is not too much. It is actually during sleep that your body uses water to help acclimate (adjust) to the atmospheric pressures of being at higher elevations.

Also, always sleep at a lower altitude than the highest point reached that day. Sleeping at least 1,500 to 2,000 feet in elevation higher that the night before has been shown to help safely acclimate the body more than sleeping higher than that altitude gain.

Cold Injuries

When traveling in cold regions, it is not always enough to put on warm clothing to protect yourself from Hypothermia and Frostbite. There are actually several ways to prevent them like being well-fed, well-hydrated and many more. These are discussed in greater detail under each Altitude Illness.

Altitude Safety: Medications

As with everything, many home and herbal remedies as well as generic treatments claim to prevent various mountain sicknesses. These treatments can make AMS worse or have other dangerous side effects – many herbs are poisonous. Only one drug is currently known to prevent AMS and to be safe for this purpose: Acetazolamide (Diamox). It causes some minor side effects, such as tingling fingers and a funny taste in the mouth. And while AMS may be the most common high altitude ailment, there are others as well — and they each have medications that may be taken either preventatively or to help alleviate symptoms once they present.

Acetazolamide (DIAMOX)

Acetazolamide prevents AMS when taken before ascent; it can also help speed recovery if taken after symptoms have developed. The drug works by acidifying the blood and reducing the respiratory alkalosis associated with high elevations, thus increasing respiration and arterial oxygenation and speeding acclimatization. An effective dose that minimizes the common side effects of increased urination and paresthesias of the fingers and toes is 125 mg every 12 hours, beginning the day before ascent and continuing the first 2 days at elevation, or longer if ascent continues.

Allergic reactions to acetazolamide are uncommon. As a non-antimicrobial sulfonamide, it does not cross-react with antimicrobial sulfonamides. However, it is best avoided by people with history of anaphylaxis to any sulfa. People with history of severe penicillin allergy have occasionally had allergic reactions to acetazolamide. The pediatric dose is 5 mg/kg/day in divided doses, up to 125 mg twice a day.


Acetazolamide is not recommended as a prophylactic medication, except under specific limited conditions outlined below:

  • • Treatment of persons with AMS.
  • • Treatment of persons bothered by periodic breathing at night.
  • • Prophylactically for persons on rapid forced ascents (such as flying into Lhasa, Tibet).
  • • Prophylactically for those persons who have repeatedly had AMS in the past.


Most people who have a reasonable ascent schedule will not need it, and in addition to some common minor but unpleasant side effects, it carries the risk of any of the severe side effects that may occur with sulfonamides.Common side effects include numbness, tingling, or vibrating sensations in hands, feet, and lips, taste alterations, and ringing in the ears. These go away when the medicine is stopped. Since acetazolamide works by forcing a bicarbonate diuresis, you will urinate more on this medication. Uncommon side effects include nausea and headache.

Source: NIH (PMC4821436)

Myths About DIAMOX

Among climbers, there are a lot of myths about acetazolamide. Let’s clarify these!


❌  Acetazolamide Hides Symptoms.

Acetazolamide accelerates acclimatization. As acclimatization occurs, symptoms resolve, which directly reflects improving health. Acetazolamide does not cover up anything – if you are still sick, you will still have symptoms. If you feel well, you are well.


❌  Acetazolamide will prevent AMS from worsening during ascent.



❌  Acetazolamide will prevent AMS during rapid ascent.

This is actually NOT a myth, but rather a misused partial truth. Acetazolamide does lessens the risk of AMS, that’s why we recommend it for people on forced ascents. This protection is not absolute, however, and it is foolish to believe that a rapid ascent on acetazolamide is without serious risk. It is still possible to ascend so rapidly that when illness strikes, it is likely to be sudden and severe, and fatal.


❌  If acetazolamide is stopped, symptoms will worsen.

There is no rebound effect. If acetazolamide is stopped, acclimatization slows down to your own intrinsic rate. If AMS is still present, it will take somewhat longer to resolve; if not – well, you don’t need to accelerate acclimatization if you ARE acclimatized. You won’t become ill simply by stopping acetazolamide.

Dexamethasone (DexPak)

Dexamethasone is effective for preventing and treating AMS and HACE and prevents HAPE as well. Unlike acetazolamide, if the drug is discontinued at elevation before acclimatization, mild rebound can occur. Acetazolamide is preferable to prevent AMS while ascending, with dexamethasone reserved as an adjunct treatment for descent. The adult dose is 4 mg every 6 hours. An increasing trend is to use dexamethasone for “summit day” on high peaks such as Kilimanjaro and Aconcagua, in order to prevent abrupt altitude illness.

Nifedipine (Procardia)

Nifedipine both prevents and ameliorates HAPE. For prevention, it is generally reserved for people who are particularly susceptible to the condition. The adult dose for prevention or treatment is 30 mg of extended release every 12 hours or 20 mg every 8 hours.

Other Medications

Phosphodiesterase-5 inhibitors can also selectively lower pulmonary artery pressure, with less effect on systemic blood pressure. Tadalafil, 10 mg twice a day during ascent, can prevent HAPE; it may also have use as a treatment. Gingko biloba, 100–120 mg taken twice a day before ascent, reduced AMS in adults in some trials. It was not effective in other trials, though, possibly due to variation in ingredients. Recent studies have shown ibuprofen 600 mg every 8 hours to be noninferior to acetazolamide in preventing AMS, although ibuprofen does not improve acclimatization or reduce periodic breathing. It is, however, over-the-counter, inexpensive, and well tolerated.

Altitude Safety 101