Acetazolamide, commonly known as Diamox, is a medication frequently used to prevent and treat altitude sickness (Acute Mountain Sickness or AMS).

For those moving up from lower to higher altitudes, on common treks like Everest Base Camp or climbing Kilimanjaro, it may assist you in reaching altitude with less stress on your body, thus making your ascent more enjoyable. You may be less prone to headaches, digestive issues, sleep disturbances and general malaise.

In my 40 years experience with Diamox, guiding groups on everything from 40 day treks across the Himalaya, to climbing Kilimanjaro, to reaching the top of Everest, with the Seven Summits completed in between, Diamox works.

And my personal experience leading my groups has been enhanced with climbs and treks with Doctors, medical researchers and a long fascination with what going to altitude does to the human body.

Standard Dosage vs. Lower Dosage

The traditional dosage for Diamox was originally 250 mg twice daily. However, research and field experience, particularly from Dr. Peter Hackett, a leading authority in high-altitude medicine, suggest a lower dosage is effective with potentially fewer side effects. Dr. Hackett, who established the high altitude clinic in Pheriche, Nepal, advocated for a dosage of 62.5 mg (normally 1/4 of a standard tablet) twice a day.

Benefits of Pre-Ascent Use

Initiating Diamox a few days before ascending to altitude may further enhance its effectiveness in preventing altitude-related symptoms such as headaches, nausea, and fatigue. For those who think they will just wait and take it if symptoms develop, it is generally too late and a higher dose of 125 mg is then recommended.

The down side of waiting until altitude symptoms develop, is that Diamox is also a diuretic.  

So your ever important need to stay hydrated will be be compromised and you will most likely be up more during the night visiting the toilet, which may be outside or a long ways down the dinghy hallway, so you won’t sleep as well.

Then you end up both tired and dehydrated, not a good combination at altitude. 

In Anchorage to climb Denali, I first stayed at Dr. Peter Hackett’s house at the time. The fact he is a very talented climber and ascended Everest, virtually solo and without ropes from the South Col in 1981, also makes his perspective particularly invaluable to his fellow high altitude climbers.

In Anchorage before I soloed Denali, (yes Denali, once Denali, always Denali),  Dr. Hackett advocated for a far lower dosage, 1/4 of a standard Diamox tablet, or 62.5 mg, morning and evening. Starting a few days in advance, before going to altitude ensured the benefits were in place once starting up to higher altitudes.

I tried it on Denali, soloing the Messner Couloir from 14.2 to the summit in 9 hours, and it certainly seemed to work. Two days later Joe Blackburn and I returned to the summit from 14.2 along the West Buttress, with little ill effects and Joe climbing quickly, having had no previous ascent above 14.2. Everyone is different, but it also seems a touch of Diamox didn’t hurt.

This dosage was further supported with a number of groups of up to 15 people I led to Tibet, and up to Everest Base Camp, where the choice was foul food or simply going to our own Base Camp and our own food quickly, ascending from Kathmandu to 5,300 metres (17,388 feet) in a matter of days.

Vinson, glacier to summit, 3,000 meters up and down the Rolex Ridge in a day.

In groups where some didn’t take Diamox, almost universally they suffered altitude symptoms and were then treating themselves with repeated doses of painkillers, feeling nauseous, and experiencing fatigue and generally feeling lousy.

I have had the good fortune to catch up with Dr. Hackett, at lectures we shared at the Smithsonian, again at an American Mountain Guides High Altitude Symposium where he led a specialized high altitude clinic for Guides and when he returned to his roots in 2010 and managed the Everest Base Camp clinic when I was guiding the peak. The 1/4 tab (or less) he commented, is still valid.

In further communications on 8 March, 2019 with Dr. Hackett, he cited just released research that specifically supported the 62.5 dosage.

This was also highlighted further in an article in 2019, still not as large a sample group as would be ideal, but supporting the reduced dosage. Interesting, they didn’t find any lessening of side effects from the 125 to 62.5 dosage – something I personally find are further alleviated at the lower dose. One would logically think these would decrease – but I’d err on the side of the data and individuals own experience here.

Dr. Hackett also commented that some people may see Diamox as an aid or form of doping, while in reality it is the opposite and will actually marginally decrease max. exercise performance – not relevant to trekkers and climbers who don’t operate anywhere near their max. “If anyone thinks it is a performance enhancing medication, it is not!”

As I walked up the Khumbu to Everest Base Camp with Peter Hillary in 2018, I saw people on everything from 250 mg, twice a day, to people who said their Doctors said that taking Diamox would mask their altitude symptoms.

In my experience, 125 or 250 mg produces dieresis to the point you spend the night up peeing and the days desperately trying to rehydrate. And not taking any, means you must go slower, or feel worse and then take other medications.

Whether people consider this an acceptable aid or not, is entirely up to them. As Peter Hillary commented when we talked of our Everest climbs, the one consistent element is: “altitude is painful”.

Perhaps making altitude a bit less painful and the heights a bit more enjoyable is okay?

This protocol is for taking Diamox in a 62.5 mg dose as prophylaxis, (in advance of going to altitude) and then when ascending. If developing AMS, the dosage still remains at 125 mg when indicated and then twice a day thereafter.

Perhaps pain and suffering is an important part of altitude, but I’d rather wake up and feel like running up the trail, than hiding under the covers, which I fear would be the alternative.

I am absolutely not a Dr., don’t prescribe Diamox and all who travel with me make their own choices. A safe protocol is certainly not ascending 1,000 meters or more a day in any case, and on our current treks with The Mountain Company we do no more than 300 meters a day of vertical, with a good rest every 1,000 metres of ascent.

Dr. Hackett, in his latest communication, also commented that the sulfa allergy we have always watched out for is no longer applicable.

“A new consensus, based on data, is that persons allergic to sulfa antibiotics do not need to avoid Diamox, which is a different kind of “sulfa” drug.”

If Diamox can help add to a mountain experience, to see a sunrise over Everest without a splitting headache or enjoy a full bowl of Sherpa stew at Gorak Shep, perhaps this protocol is something you may consider after discussions with your Doctor. (though I must add, some Drs. have limited or no experience with Diamox, and are seeing old data and studies that have been proven wrong).

And if you can climb Kilimanjaro (the latest and greatest video of our complete ascent is here), as I did again with a Jagged Globe group of 10 people in 2024, without a single person exhibiting any altitude symptoms, and 100% success in reaching the summit, perhaps it will have something to add to your own high altitude experience.