Diamox (Acetazolamide) has been tried in the treatment and prevention of AMS. The research literature is large and contains some conflicting conclusions. Here we cover only acetazolamide (trade name Diamox), which has been studied thoroughly over 25 years.

Your blood has to maintain a finely tuned balance for bodily functions to work well. When you hyperventilate (pant), as when over-exerting at altitude, you lose a lot of carbon dioxide which can reduce the acidity of your blood. Diamox blocks or slows the enzyme involved in converting carbon dioxide. As a result, it speeds up acclimatisation by stopping the blood from becoming too alkaline and by smoothing out your breathing: it also reduces periodic breathing. Diamox allows you to breathe faster so that you metabolize more oxygen, thereby minimizing the symptoms caused by poor oxygenation. This is especially helpful at night when respiratory drive is decreased. . Many people who attempt high altitude climbs take Diamox with them because it can help to prevent, as well as treat, AMS. Before rushing off to get a doctor's prescription, however, consider the possible side-effects.

Diamox has been known to cause severe allergic reactions in a few individuals. So you should try it out ahead of your trip to test if you are allergic, to experiment with dosage and to discover whether you can tolerate the side-effects which may include:

• increased flow of urine (diuresis)
• numbness or tingling in hands, feet and face
• nausea
• finding that carbonated drinks taste flat.

Since altitude has a diuretic effect anyway, many people prefer to avoid Diamox, wishing to avoid further interruptions to sleep in order to urinate. This may be a problem only when dosage is too high; individuals vary so much that you may have to establish your own dosage: not easy if it is your first high-altitude trek. At one time, the recommendation was to take 250 mg three times a day, starting several days before the ascent. Two recent authorities (Houston 1998 and Bezruchka 1994) suggest starting with 125 mg daily at bedtime starting only on the day before ascent, and increasing this to up to 250 mg twice a day only if need be. The recommendation of the Himalayan Rescue Association Medical Clinic is 125 mg. twice a day (morning and night). (The standard dose was 250 mg., but their research showed no difference for most people with the lower dose, although some individuals may need 250 mg.)

These dosages are suggested when using Diamox as a preventive measure. In treating AMS, the higher dosages should be used and descent is strongly recommended. Although the medical authorities tend to favour Diamox, I noticed no difference in acclimatisation between the members of two holiday groups according to whether they used the drug. As many people who were taking Diamox suffered symptoms as did those who took nothing. Because of the small numbers involved, this has no scientific validity, but it shows that taking Diamox doesn't necessarily prevent AMS

It is recommended to trial course of the drug before going to a remote location where a severe allergic reaction could prove difficult to treat.