Preventing AMS

People acclimatize at different rates, so no absolute statements are possible, but in general, the following recommendations will keep most people from getting AMS:

  • If possible, you should spend at least one night at an intermediate elevation below 3000 meters.
  • At altitudes above 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300-500 meters (1000-1500 feet) per night.
  • Every 1000 meters (3000 feet) you should spend a second night at the same elevation.

Remember, it's how high you sleep each night that really counts; climbers have understood this for years, and have a maxim "climb high, sleep low". The day hikes to higher elevations that you take on your "rest days" (when you spend a second night at the same altitude) help your acclimatization by exposing you to higher elevations, then you return to a lower (safer) elevation to sleep. This second night also ensures that you are fully acclimatized and ready for further ascent.

Things to Avoid

Respiratory depression (the slowing down of breathing) can be caused by various medications, and may be a problem at altitude. The following medications can do this, and should never be used by someone who has symptoms of altitude illness (these may be safe in persons who are not ill, although this remains controversial):

  • Alcohol 
  • Sleeping pills (acetazolamide is the sleeping tablet of choice at altitude) 
  • Narcotic pain medications in more than modest doses


Under certain circumstances, prophylaxis with medication may be advisable.

  • for persons on forced rapid ascents (such as flying into Lhasa, Tibet, or La Paz, Bolivia), for climbers who cannot avoid a big altitude gain due to terrain considerations, or for rescue personnel on a rapid ascent
  • for persons who have repeatedly had AMS in the past


We do not recommend acetazolamide as a prophylactic medication, except under the specific limited conditions outlined above. 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.

The dose of acetazolamide for prophylaxis is 125-250 mg twice a day starting 24 hours before ascent, and discontinuing after the second or third night at the maximum altitude (or with descent if that occurs earlier). Sustained release acetazolamide, 500 mg, is also available and may be taken once per day instead of the shorter acting form, though side effects will be more prominent with this dose.

Ginkgo biloba extract

Some early work with Ginkgo biloba extract was encouraging with regards to its use in preventing AMS, but some recent large, well-designed studies have shown no benefit.

 AMS Prophylaxis: 
 Acetazolamide (Diamox┬«) 
 125-250 mg (depending on body weight; persons over 100 kg (220 lbs) should take the higher dose) twice a day starting 24 hours before ascent, and discontinuing after the second or third night at the maximum altitude (or with descent if that occurs earlier). Children may take 2.5 mg/kg of body weight twice a day. 

Preventing Severe AMS

This simply cannot be emphasized too much. If you have symptoms of AMS, do not ascend any higher. Violating this simple rule has resulted in many tragic deaths.

If you ascend with AMS you will get worse, and you might die. This is extremely important - even a day hike to a higher elevation is a great risk. In many cases of High Altitude Cerebral Edema, this rule was violated. Stay at the same altitude (or descend) until your symptoms completely go away. Once your symptoms are completely gone, you have acclimatized and then it is OK to continue ascending. It is always OK to descend, you will get better faster.