Climbing (or trail running) mountainous ranges can be exhilarating as well as a dangerous experience for those who dare. Depending on individual capacity, altitude sickness can appear in mountain climbers any time between 8000 to over 12000 feet above ground level. Often at times, altitude sickness is dependent on the climbing speed of the individual rather than the height itself.

[This post is provided by Dr Felix in UK. It relates to climbing, but it applies too for running. This information should help runners preparing for Nepal’s Mustang and Manaslu Trail Races. Enjoy, and please ask any further questions at the bottom.

And before reading, athletes, please note this from high altitude doctor, Suvash Dawadi.

I write this email to suggest some additions to FAQs and information regarding use of acetazolamide (Diamox) use in races in Nepal. I think we should point out on the website itself that Acetazolamide is on the list of banned substances both in and out of competition by World anti-doping Agency. While this might be OK for an amateur racer,  I know we have a few competitions who are involved in races elsewhere including road races and marathons. So it might be a good idea to just put something about the possible doping issue. Also if anyone who does participate in WADA governed sport decides to take diamox as prophylaxis,  he/she should fill a Therapeutic Use Exemption (TUE)  form with their respective doping agencies. If you have an athlete should require treatment with Diamox,  again they have to notify the authorities back home and file for a retroactive TUE. Dr Suvash Dawadi

Cause of Altitude Sickness

People have a hard time climbing up heights because of the environmental change they have to face at elevated levels. Normal quantity of oxygen is 21% in air on ground, with air pressure around 760mmHg. At elevated levels, air pressure starts decreasing, so the number of oxygen particles in the air reduce in correlation. For example, air pressure at 12,000 feet high altitude is only 480mmHg approximately, so the body has to adjust the 40% less amount of oxygen in air at that specific height (Swenson & Bärtsch, 2014).

Moreover, lower air pressure and higher altitude also produces fluid build-up as it disturbs internal blood pressure, while forcing red blood cells to work more in order to cope with lost oxygen levels.

Advantage of Diamox


Diamox tablets for altitude acclimatisation

Diamox is a prescription medicine also sold under its generic name acetazolamide which can reduce and prevent altitude sickness (West, et al., 2007). It helps in reducing the shortness of breath, dizziness, nausea, fatigue and headaches, which commonly occur at high altitude. Moreover, it reduces the bodily fluid build-up that occurs with low air pressure.

Avoid Cheyne Stokes Respiration

Cheyne Stokes respiration is a condition that many people experience at high altitudes. This occurs normally during the sleeping period at higher altitudes. Your body breathes periodically, alternating between no breathing, and heavy breathing (Netzer, et al., 2013). Not only does this condition cause trouble for the climbers, but it can also scare them. By taking Diamox at night, Cheyne Stokes can be reduced and climbers can sleep better.

Usage Instructions for Climbers

Altitude sickness is best prevented by planning ahead. Start taking Diamox at least 24 hours before you start your climbing adventure and continue throughout your climb. Stop your Diamox at least 48 hours after you have finished climbing. At times, you may need to continue for the entire duration of your stay at high altitude. If altitude sickness gets severe, stop relying on Diamox and descend as soon as possible. Doctors normally recommend a dosage of 125mg or a 250mg tablet, to be administered twice a day.

Care during Diamox Intake

Diamox is a diuretic and reduces potassium levels in the body. Therefore, it is recommended that while you are taking Diamox, you should drink as much water as possible. Moreover, you should stick to a high-potassium diet such as bananas, green vegetables and oranges while you’re on Diamox. Diamox which contains the active ingredient acetazolamide should be avoided if in case the patient has low blood levels of potassium or sodium, adrenal gland problem, kidney or liver disease.

Consider Acclimatisation

Acclimatisation is the process of ascending elevated heights at a slow pace. For example, if you climb up a steep mountainous range such as Kilimanjaro, you will be at a greater disadvantage as compared to trekking over low peaks and ridges. Once you have covered 10,000 feet above ground, make an aim of climbing only 300-500m height in 24 hours. Climbing at this pace can help prevent mountain sickness altogether (DrFelix, 2014).

Consult a Doctor Immediately

There are two dangerous conditions associated with altitude sickness that require immediate medical attention, and cannot be treated with Diamox. First condition is the accumulation of fluid in the lungs, termed as High Altitude Pulmonary Oedema (HAPE) (Bock & Hultgren, 1986). If you feel extremely short of breath while everyone else is back to normal, you need to seek help immediately.

Second condition is the accumulation of fluid in the brain, termed as High Altitude Cerebral Oedema (HACE). Symptoms of HACE include loss of coordination, lethargy and general change in behaviour. Moreover, HACE can also cause cognitive impairment (Zafren, 2000).

In case of either HACE or HAPE, it is urgent that the patient should descend at least 500 to 1000 meters below the current altitude, and should not be delayed. Moreover, the patient should be administered hyperbaric oxygen and oxygen steroids.

Concluding Thoughts

High altitudes require great respect. If you consider yourself to be a muscular and strong person, do not assume that you can battle your way through to high places. Often, people who are overconfident about their strengths are the ones who struggle the most at high places. Take your medicine as prescribed, follow best practice for climbing and all the safety rules for successful climb and a good experience. You can order altitude sickness tablets from UK registered online doctor & pharmacy services like at a reasonable cost and have it delivered to your home before you set off for your climb.


Bock, J. & Hultgren, H. N., 1986. Emergency Maneuver in High-Altitude Pulmonary Edema. JAMA, 255(23), pp. 3245-3246.

Netzer, N. et al., 2013. Hypoxia‐Related Altitude Illnesses. Journal of Travel Medicine, 20(4), pp. 247-255.

Swenson, E. R. & Bärtsch, P., 2014. High Altitude: Human Adaptation to Hypoxia. New York, NY: Springer New York.

West, J. B., Schoene, R. B., Milledge, J. S. & Ward, M. P., 2007. High altitude medicine and physiology. 4th ed. London, UK: Hodder Arnold.

Doctor Felix. 2014. High Altitude Sickness. [ONLINE] Available at: [Accessed 10 January 2016].

Zafren, K., 2000. Understanding medical problems associated with high altitude. Emergency Medicine, 32(9), p. 90.



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