California Institute of Technology

Altitude Info and Links

Altitude Sickness links

    Altitude sickness is a broad term that includes Acute Mountain Sickness (AMS) as well as the more serious HAPE and HACE (note: in AMS, acute is a technical term that means rapid onset, as opposed to being synonymous with severe). Clearly, the best method to avoid sickness is gradual ascent, and the best method to deal with symptoms is rapid descent. This page deals with second choice options, and in particual, the every fascinating subject of drugs. Climbers have tried different drugs to combat altitude sickness, including acetazolamide (aka Diamox), dexamethasome (aka Decadron), Nifedipine, Sildenafil (aka Viagra) and ginkgo biloba extract.

    Before using these drugs, it is wise to learn more about them and I supply a few links below to get you started. I have personally only used over-the-counter ginkgo biloba; old studies suggested it alleviates altitude headaches, though I think new studies have shown that this is not for certain. It is cheap and safe, however, and readily available. See this summary about Ginkgo Biloba by Dr. Peter Hackett. [Some recent 2009 articles on Ginkgo done by Hackett and coauthors (see "Ginkgo biloba does -- and does not -- prevent AMS" and "Ginkgo Biloba for the prevention of AMS" on pubmed) conclude that gingo extract is not standardized well enough to draw meaningful conclusions -- some brands work, others don't].

    In general, for climbing the Sierras, it is possible, though unlikely to develop more serious forms of Altitude Sickness. Because it is so unlikely, most parties will not have strong drugs like Acetazolamide or Decadron, and hence if a serious condition does develop, the only solution is quick descent to the valley.

  • Dr. J. Evans approached the club in fall 2006 and asked about volunteers for trying his new altitude supplement. Here are his papers that provide a nice summary (though not peer-reviewed) of the mechanisms involved in altitude sickness. You need the username and password to access the documents, per his request (email alpine). Evans seems to subscribe to the Nitric Oxide theory (see Houston's book for some background).
  • LA Times article on using Viagra to prevent pulmonary edema
  • If you're only going to read one article, this one is a pretty good choice: A nice "tutorial" on altitude sickness From the International Society for Mountain Medicine (ISMM).
  • High Altitude Medicine .com
  • A brief overview of AMS from
  • Wikipedia entry on Diamox
  • Wikipedia entry on Decadron
  • Wikipedia entry on altitude sickness
  • The archives of the Wilderness and Environmental Journal Published by the Wildnerness Medical Society ( The current volume is for paid subscribers or members only, but the archives are public. Incidentally, the Caltech Library has a subscription, but the link doesn't seem to work. This is the first stop to go if you are looking for peer-reviewed articles.
  • Information from the Merck manual (update: that link is now bad. Try this one). Quite nice, and worth quoting part of it (boldface is mine):

      "Altitude sickness is best prevented by slow ascent, but the safe rate of ascent varies among individuals. Most can ascend to 5000 ft (1500 m) in 1 day without symptoms, but many are affected by ascending to 8000 ft (2500 m). Above this level, a rate of 1500 ft (460 m)/day is advisable. Climbers should learn how fast they can ascend without developing symptoms; a climbing party should be paced for its slowest member. Although physical fitness enables greater exertion with less O2 consumption, it does not protect against any form of altitude sickness. Strenuous effort should be avoided for 24 to 36 h after the ascent is completed, but bed rest is less beneficial than mild exercise.

      "Drinking much more water than usual is important, because overbreathing dry air at altitude greatly increases water loss, and dehydration with some degree of hypovolemia aggravates symptoms. Additional salt should be avoided. Alcohol seems to worsen AMS and diminishes nocturnal ventilation, thus accentuating sleep disturbance. Eating frequent small meals that are high in easily digested carbohydrates (eg. fruits, jams, starches) improves altitude tolerance and is recommended for the first few days.

      "Acetazolamide 125 mg at bedtime (for most persons) or 125 mg q 8 h is an effective prophylactic for AMS. Sustained-release capsules (500 mg once daily) are also available. Starting acetazolamide before the ascent has no advantage. Acetazolamide inhibits carbonic anhydrase, increasing ventilation and allowing better O2 transport with less alkalosis; it eliminates periodic breathing (almost universal during sleep at high altitude), thus preventing sharp falls in blood O2. Acetazolamide should not be given to patients allergic to sulfa drugs. Low-flow O2 during sleep has the same effect but is inconvenient. Analogs of acetazolamide offer no advantage. Antacids are useless for prevention. Dexamethasone, which minimizes symptoms of AMS, is not recommended for prevention.

      "Retinal hemorrhages require no treatment, generally resolving while the climber remains at high altitude.
      AMS seldom requires treatment other than fluids, analgesics, a light diet, mild activity, and (rarely) descent. Dexamethasone 4 mg po q 6 h is effective; acetazolamide 250 mg po q 6 h may alleviate symptoms.

  • The high-altitude brain, T.F. Hornbein, J. Exp. Biol. Sep. 2001 (18). This is the abstract from PubMed. Hornbein is also (or was) a noted climber. He and Willi Unsoeld were the first to climb the West Ridge of Everest in the 50s, and survived a high-altitude bivouac. Also, it turns out this issue of the Journal of Experimental Biology is devoted to hypoxia research. If you have access (eg. all Caltech users), you can view the issues's contents. Here is the full-text html form of Thomas Horbein's article.
  • Here are two articles about antioxidants; they may be more useful for their links

  • Oxidative Stress in Humans Training in a Cold, Moderate Altitude Environment, Schmidt et al, Wilderness and Environmental Medicine Vol. 13, no. 2 pp 94. Full text from WMS site or abstract via Pub Med (with link to full text). About antioxidants (e.g. vitamins C and E, lipoic acid, ginkgo biloba) for longer term exposure to altitude. Basic conclusion: antioxidants only useful for people who have low antioxidant status (regardless of altitude).
  • Work at high altitude and oxidative stress: antioxidant nutrients, E.W. Askew, Toxicology Vol. 180, Issue 2, p. 107. Nov. 2002. Abstract via science direct, or if you have access (e.g. all JPL users, but not plain Caltech users), they have the full text. If you have a Caltech IP or know the alpine club password, you can access a full text pdf here.

Dehydration and altitude

Follow almost any altitude link on this page and it will tell you to stay hydrated! Certainly very good advice. But, there are a few things to consider. Here are two points from the Institude for Altitude Medicine (IFAM) in Telluride, Colorado (where Dr. Peter Hackett works):

  • Myth # 1 - Don't drink caffeine at altitude.
    We don't know where this false assumption came from, but likely from the fact that caffeine is a mild diuretic (makes you pee). The concern is that it could dehydrate you and contribute to altitude sickness. This concern is unfounded unless you drink pots of black sludge coffee a day and little else. In reality, caffeine stimulates your brain, kidneys and breathing, all of which are helpful at altitude. And for those people who drink several caffeinated beverages a day, stopping abruptly can cause a profound headache.
  • Myth #4 - Drinking extra water will protect you from altitude illness.
    Staying hydrated is important at altitude. Symptoms of dehydration are similar to AMS. In reality you only need an additional liter to a liter and a half of water at altitude. Too much water is harmful and can dilute your body's sodium levels (hyponatremia) causing weakness, confusion, seizures, and coma. A good rule of thumb to assess for hydration is to check your urine. Clear urine indicates adequate hydration, dark urine suggest dehydration and the need to drink more water.

Also very interesting is this excerpt from a NOVA interview with Dr. Peter Hackett: (note: he is probably referring to HACE; I am unsure whether he implies that his extends to general AMS as well)

NOVA: You've said it is best to be dehydrated at altitude because a dehydrated brain doesn't swell at altitude.

PETER HACKETT: There's evidence that the people who do best at altitude are dehydrated. That is the body resets the serum of molality level which has to do with the water balance. And the body, for some reason, prefers to be dry at high altitude. My own thinking is that this is good for the body because it keeps the brain a little bit drier and softer. So that if it does start to accumulate a little water or get a little swelling, it can be tolerated better.

More advice from Peter Hackett, on a slightly different topic, comes via a mention in Colby Coombs "Denali's West Buttress" book. In this book, Colin Grissom, M.D., writes a few pages on altitude illness, and writes the following slightly cryptic sentences:

Researchers continue to study and attempt to understand why some people acclimate to altitude and others do not. Hackett believes "lazy breathers," particularly long-distance runners, are most likely to experience altitude related problems. HACE and HAPE afflicts the strong and weak alike, althought being aerobically fit provides a definite advantage...

I wasn't able to find the origin of this. A quick google search for "lazy breathers" doesn't turn up much (nothing in wikipedia or pubmed) other than stuff on yoga and public speaking; it seems that it is a lay term for not breathing deeply (and that 99% of the population are lazy breathers). So this remains a mystery...

Charles Houston's advice

Dr. Charles Houston was the expert on altitude sickness until his death, at age 96, in September 2009. His track record in both the mountaineering world and the medical world is unparalleled. His "street-cred" came from being on the first-ascent party to Nanda Devi in 1936, then leading an expedition to K2 in 1938, and being part of the famous 1953 American K2 expedition (the one with the famous belay of Pete Shoening). He begain studying high-altitude effects on humans in World War II and lead Operation Everest, which studied altitude effects on pilots (and again leading Operation Everest II in 1985). From 1967 to 1979, he was based at the 17,500' lab on Mount Logan in the Canadian Yukon. Perhaps the only other medical researcher with such street-cred is Dr. Peter Hackett, who ran the lab at the 14,200' camp on Denali from 1982 to 1989.

So, Houston's book Going Higher: Oxygen, Man and Mountains (1st edition was from 1980; the club has the 1998 4th edition in our library; part of the 2005 5th edition is on Google Books: update, 2010, we now have the 2005 5th edition in our library) is the bible for alpinists (or "arm-chair" doctors). Read the book! Below are just a few snippets of his advice for those of you without access to the book.

    Houston's advice
  • on Acetazolamide (Diamox): "At first the recommended dosage was 250 mg three times a day, starting several days before the ascent. This increased urination, especially at night, and caused some unpleasant symptoms. Then the recommended dosages was reduced to 125 mg twice a day; I generally recommend 125 mg once a day, at bedtime. This is effective for most people, causes few symptoms, and does not increase urine flow at night. If this does not prevent symptoms, I advise increasing the dose to 250 mg twice a day, and starting only on the day of the ascent. It's important to tailor the dose to a person's experience or wishes, and over time an ideal dose can be found. Older authorities and many articles and books still suggest the larger dose. Because Diamox is an enzyme inhibitor and acts rapidly, perhaps you don't need to take it several days before starting your climb, as is sometimes advsised. Delayed-action pills provide a larger dose, but by a sustained slow release, which some like. I prefer the regular form so the dose can be adjusted if needed."
  • "We have good theoretical reason to believe that a diet that is very high in carbohydrate and contains virtually no fat or protein will decrease mountain illnesses. In practice, though, such a pure carbohydrate diet becomes too distasteful after a day or two and really is hard to accept. Recent studiesn of a diet that is 70 percent carbohydrate have shown no benefit in preventing mountain sickness.
    "Generally accepted is a game plan for eating frequent small high-carbohydrate snacks during the day, and adding protein at night. A few special high-carbohydrate probducts have been touted, but so far no well-controlled study at altitude has been reported."
  • on Viagra (p. 103 5th ed): "A very low dose of Viagra [sildenafil citrate], 25 mg every three hours, has proven to be more effective than nifedipine (a drug that dilates arteries) in treating HAPE, and Viagra does not have as strong a tendencay to lower blood pressure as nifedipine has. Whether or not the longer-acting analof of Viagra, marketed under the brand name Cialis, will be suitable for HAPE susceptibles to take prior to a high climb remains to be tested."
  • on ROS (p. 103-4 5th ed; ROS stands for Reactive Oxygen Species, known as "free radicals" in popular literature): "Elevated ROS levels predispose the climber at high altitude to both HAPE and HACE in several ways..."

    "If elevated ROS levels lead to HAPE and HACE, shoudl climbers at altitude simply flood their systems with antioxidants such as vitamin E to reduce these chemicals? There is no clear answer to thsi question, but caution is probably in order. Low levels of ROS serve several important positive fucntiions in the cells. THey are needed for the production of thyroid hormone and for optimal force production by muscle. Perhaps most important, ROS serve as part fo the natural cellular defense against infection, and inflammation from lung infections can increase the likelihood of HAPE. In light of this, it is probably not surprising that studies of the use of antioxidants to prevent HACE and HAPE suggest they do not help in staving off mountain sickness."

    [another possible benefit of high ROS levels]:
    "ROS may also play a role in acclimatization to altitude. ... Over time at high altitude, ROS can stimulate or induce iNOS activity, leading to increased NO [ed.: this is nitric oxide, not nitrous oxide] production. Thus, climbers ascending to altitude may initially experience reduced NO levels but later achieve elevated levels. This NO may block inflammation in the lung and brain and dilate pulmonary blood vessels, contributing to the reduced inflammation and pulmonary artery pressures that occur during the process of acclimitization."
  • on EPO (p. 107-8 5th ed; EPO is Erythropoietin, used in the cycling world as an illegal doping drug):
    "EPO... stimulatse bone marrow to produce red blood cells. Hypoxia [lack of oxygen]... activates previously dormant EPO-producing cells. ... Increased EPO levels are responsible for the high red blood cell concentration (high hematocrit) we see in those who live at high altitude for extended periods and in those with severe lung disease.

Misc. supplement info

    Caffeine has mixed effects, and it certainly isn't recommended unconditionally, but it is worth looking into. It is often avoided in the mountains because of its diuretic properties (which are generally much milder than popular belief). Not all similar substances are diuretic, eg. taurine is not. Also, caffeine is only a weak diuretic and probably does not present a problem; see this summary article or the real journal article, or Caffeine article by Armstrong et al in Exercise and Sport Sciences Reviews, which is summarized here:

    In his review, Caffeine, Body Fluid-Electrolyte Balance, and Exercise Performance, Lawrence E. Armstrong, a professor of exercise physiology at the University of Connecticut disproves the notion that caffeinated beverages rob us of our precious fluids. By reviewing the scientific research on the subject, he concludes that although caffeine, like water, is a mild diuresis (it increases excretion of urine), moderate caffeine consumption does not produce a fluid-electrolyte imbalance that can affect health or exercise performance. Furthermore, we retain roughly the same amount of fluid after drinking a caffeinated beverage as we do after drinking water.

    Even more encouraging for habitual coffee consumers is the finding that those with caffeine tolerance have reduced likelihood that a fluid electrolyte imbalance will occur. The more regular your caffeine habit, the more fluid your body is conditioned to retain.

    Benefits of caffeine

    Caffeine almost certainly increases endurance. Go to pubmed and search for "caffeine endurance" and you'll find lots of papers, such as: Additionally, coffee has anti-oxidant effects (much more than tea), though it also has reactive oxygen. See the Aug. 15th, 2006 NY Times article "Coffee as a Health Drink? Studies Find Some Benefits".


    Extremely important for high altitude! Exercise and altitude both increase production of Reactive Oxygen Species. See Aug, 2006 New Scientist article about antioxidants in general. Despite the article listing evidence against supplements in the general population, they appear to be somewhat effective at high altitude for prevenging AMS symptoms. The New Scientist artile also gives a list of foods with high levels of antioxidants. In short, eat lots of pecans on your trips above 12,000'.


To quote from the abstract of "Garlic as an anti-fatigue agent" (Mol Nutr Food Res 2007), "More than three thousand publications in the past have confirmed the efficacy of garlic for the prevention and treatment of a variety of diseases, acknowledging and validating its traditional uses." Basically, the stuff has been used for everything, and it appears it may have some use for mountaineering (due to its effects on circulation -- so not just for high altitude, but also for any exercise or any outing in cold weather).

For example, "Garlic prevents hypoxic pulmonary hypertension in rats" (AM J Physiol 1998) discusses garlic and altitude a bit (from the abstract: "Hypoxic pulmonary vasoconstriction underlies the development of high-altitude pulmonary edema. Anecdotal observations suggest a beneficial effect of garlic in preventing high-altitude symptoms...")

From Climbing: training for peak performance(2002) by Clyde Soles, we have:

Garlic. Garlic has been used for millennia to help thin the blood. Four large cloves of raw garlic per day, or 2 grams of garlic powder, might improve blood flow in the lungs by reducing pulmonary vasoconstriction. It's been shown effective in rats, but no human studies have confirmed the results. Unfortunately, cooking deactives the active ingredient (allicin), though other compounds are released that may also be beneficial.

From Extreme alpinism: climbing light(1999) by Mark Twight, we have:

Garlic. Garlic is an essential cold-weather supplement. It's a better anti-clotting agent than aspirin and reduces the stickiness of platelets, which improves overall blood circulation. Look for a garlic supplement with a standardized amount of S-allyclysteine, the strongest-acting pharmacological compound in garlic. Saponins, steroid-like compounds found in garlic, inhibit an enzyme in the muscle cells of the arteries, resulting in arterial dilation and reduced blood pressure, thus better circulation. Reinhold Messner used garlic supplements for high-altitude climbing because physiologists claimed they improved vascular elasticity. Both dry and liquid forms of garlic supplements also increase the number of natural killer cells in the body, improving immunity and reducing the risk of cancer.

Of course, bear in mind that Soles and Twight are not doctors...

Thinning the blood

Acclimitization means the blood becomes rich with plateles, making it thick. Some medicines thin the blood (which may be desirable), so it may be wise to avoid taking more than one such medicine. From Climbing: training for peak performance by Clyde Soles, we have:

Aspirin. For over a century, mountaineers have been taking aspirin to combat headaches at altitude. Other over-the-counter painkillers, such as ibuprofen and naproxen, work as well. However, aspirin also helps thin the blood, so it might help performance at very high altitude. Do not take aspirin with ginkgo biloba or high doses of garlic because they can increase the tendency to bleed.

Cautions: Acetazolamide has unwanted side-effects, and most of the other strong altitude medicines have worse side-effects, so don't pop these pills on Mt. Whitney unless you absolutely need them. And of course, drugs may interact with each other. No website is a substitute for advice from your personal physician. This website was not written by a doctor!