Sit in any lodge dining room above 3,000 m and the conversation will reach Diamox within ten minutes. Are you taking it? When did you start? Doesn't it just hide the symptoms? Half the answers offered will be wrong.
Diamox is the brand name of acetazolamide, a drug that has been used in altitude medicine for decades. It is well studied, it is recommended in the main international guidelines for preventing acute mountain sickness in people at moderate or high risk, and it is neither a magic shield nor a dangerous crutch. It is a useful tool for some trekkers on some routes.
This article is general information for trip planning, not medical advice. Acetazolamide is a prescription medicine. The doses given here are those commonly published in altitude medicine guidance; your own doctor must decide whether it suits you and at what dose.
What Diamox Actually Does
When you go high, low oxygen makes you breathe faster. Faster breathing blows off carbon dioxide, which makes your blood slightly alkaline — and that alkalinity tells your brain to ease off breathing again. For the first few days your body is held back by its own brake.
Your kidneys eventually fix this by excreting bicarbonate, which re-acidifies the blood and lets breathing rise to where it needs to be. That is a large part of what acclimatisation is. It takes several days.
Acetazolamide makes the kidneys excrete bicarbonate sooner. In effect it gives you, within about a day, the blood chemistry that would otherwise take several days to develop. You breathe more, particularly at night, and your oxygen levels are better for it.
- It speeds up a natural process. It is real acclimatisation, arrived at faster.
- It does not mask symptoms. If you develop altitude sickness while taking it, you will know.
- It smooths out night-time breathing, reducing the stop-start pattern that wakes people at altitude.
- It does not make a fast ascent safe. People taking Diamox still get altitude sickness if they climb too quickly.
Who Should Consider It
Guidelines sort trekkers into risk groups by two things: how fast the itinerary gains sleeping altitude, and whether you have had altitude illness before. Preventive medication is generally suggested for moderate and high risk, and not needed for low risk.
| Risk | Typical situation | Examples in Nepal | Usual advice |
|---|---|---|---|
| Low | No history of altitude illness; sleeping below about 2,800 m, or a gradual ascent with rest days | Poon Hill; village treks below 3,000 m; Kathmandu Valley rim walks | Not normally needed |
| Moderate | No history, but going from low altitude to above 2,800 m in a day; or gaining more than 500 m of sleeping altitude a day above 3,000 m, with rest days | Flying to Lukla for Everest Base Camp; Langtang; Annapurna Base Camp; Mardi Himal | Worth considering; discuss with your doctor |
| High | Previous altitude sickness with a fast ascent; any history of HAPE or HACE; reaching above 3,500 m in a single day | Driving to Manang; flying to Jomsom and driving to Muktinath the same day; helicopter tours with a landing; trekking peaks | Generally recommended, alongside a slower plan |
Notice what moves people into the high-risk row: vehicles. Roads now reach Manang and Muktinath, and a jeep can take you from 800 m to 3,700 m in a day — something no walker could do. If your itinerary includes a drive or flight to altitude, the case for medication is much stronger. See our guide to the Annapurna Circuit road.
Dose and Timing
| Commonly published guidance | |
|---|---|
| Preventive dose (adults) | 125 mg twice a day — morning and evening |
| When to start | The day before you ascend above about 3,000 m, or before a rapid ascent |
| How long to continue | Until you have spent two to three days at your highest sleeping altitude, or until you begin to descend |
| Stopping | Simply stop. No tapering is needed and symptoms do not rebound |
| Treatment dose | 250 mg twice a day for established mild altitude sickness — together with stopping the ascent |
| Children | Dosed by body weight; a doctor must calculate it |
- Tablets in Nepal are usually 250 mg. For the preventive dose they are broken in half. Tablets bought at home may be 125 mg or 250 mg — check the packet.
- Take the evening dose with dinner, not at bedtime, or you will be up through the night.
- Drink more than you think you need. It is a mild diuretic.
- Older advice recommended 250 mg twice daily for prevention. The lower dose works as well for most people with fewer side effects.
- Missed a dose? Take the next one as normal. Do not double up.
On a standard Everest Base Camp itinerary, many trekkers start in Kathmandu the day before the Lukla flight, or at Namche, and continue until they turn downhill from Gorak Shep. On the Annapurna Circuit, the usual pattern is to start before Manang and stop after crossing Thorong La. Your doctor's instructions take priority over any pattern described here.
Side Effects You Will Probably Notice
| Effect | How common | What to do |
|---|---|---|
| Tingling in fingers, toes and lips | Very common | Harmless. It comes and goes |
| Passing urine more often | Very common | Drink more. Take the evening dose early |
| Fizzy drinks and beer taste flat or metallic | Common | Nothing — and no loss, given beer is a bad idea at altitude |
| Mild nausea, reduced appetite | Occasional | Take with food |
| Tiredness or drowsiness | Occasional | Usually settles after a day or two |
| Blurred vision | Rare | Stop and seek medical advice |
| Rash, especially with fever or blisters | Rare but serious | Stop immediately; descend and get medical help |
| Swelling of lips or face, difficulty breathing | Very rare — an allergic reaction | Emergency. Stop the drug and get help at once |
The awkward thing is that nausea and tiredness are also symptoms of altitude sickness. This is one reason to try the drug at home first — so you know what it feels like on you before altitude is added to the picture.
Who Should Not Take It
Tell your doctor about all of these before asking for a prescription.
- Sulfonamide allergy. Acetazolamide is a sulfonamide. Many people with a mild reaction to sulfa antibiotics tolerate it, but anyone who has had a severe reaction — anaphylaxis or a severe blistering rash — should avoid it. This needs individual medical advice.
- Significant kidney or liver disease.
- Pregnancy and breastfeeding. Generally avoided unless a doctor judges the benefit outweighs the risk.
- Low sodium or potassium levels, or adrenal gland problems.
- Certain other medicines: high-dose aspirin, some anti-epileptic drugs, lithium and others. Give your doctor a complete list.
- A history of kidney stones. Mention it; short courses are usually acceptable but it is your doctor's call.
- Diabetes. Not a bar, but it can affect blood chemistry, so plan it with your doctor.
If you cannot take acetazolamide, the alternative is not another tablet you pick yourself. It is a slower itinerary — an extra night at Namche, an extra day at Manang — and, where a doctor advises it, a different preventive drug. We can adjust any itinerary to add acclimatisation days.
Try It at Home First
- Two to three weeks before you travel, take the dose your doctor prescribed for two days.
- Note what you feel: tingling, more trips to the toilet, any nausea or tiredness.
- Report anything beyond the common effects to your doctor — particularly a rash.
- If you tolerate it, you start the trek knowing what is the drug and what is the mountain.
- If you do not, there is still time to plan a slower ascent instead.
This simple step is skipped by most trekkers and recommended by most altitude doctors. Discovering an intolerance at 3,500 m, a day's walk from anywhere, is a poor alternative.
Myths Worth Dropping
| Myth | Reality |
|---|---|
| It masks the symptoms of altitude sickness | It does not. It treats the cause of mild symptoms by speeding acclimatisation. If you get worse on it, you will feel worse |
| Once you start you cannot stop until you are down | You can stop at any time. There is no rebound |
| It is cheating | It accelerates the same adaptation your kidneys would make anyway |
| If I take it I can skip the rest days | No. People on Diamox who ascend too fast still get ill, including seriously |
| It dehydrates you dangerously | It is a mild diuretic. Drink an extra litre |
| Garlic soup works just as well | Garlic soup is a lodge tradition and a good way to take in fluid and salt. There is no evidence it prevents altitude sickness |
| Fit people do not need it | Fitness does not protect against altitude sickness at all |
| Start it only when you get a headache | That is treatment, at a higher dose, and you must also stop ascending. Prevention is started the day before |
Diamox Is Not the Plan
The plan is the itinerary. Above 3,000 m, raise your sleeping altitude by no more than about 500 m a night, take a rest day every three or four days, drink enough, walk slowly, and tell your guide about symptoms when they start. A trekker who does all that without Diamox is safer than one who takes it and breaks the rules.
And whatever you are taking, the response to worsening symptoms is the same: stop going up, and if they do not improve, go down. Our altitude sickness guide sets out the rules, and the Everest Base Camp altitude profile shows how a well-built itinerary applies them.
We Provide This Service: Pre- and Post-Trek Health Support
Green Compass Treks does not prescribe Diamox or any other medicine — that decision belongs to you and your doctor. What we provide is everything around it.
- Before you travel: the day-by-day sleeping altitudes of your itinerary, so your doctor can judge your risk group and advise on timing.
- Itineraries built on the acclimatisation rules, with rest days at the right heights, and extra days added on request for anyone who cannot or prefers not to take medication.
- On arrival: a health briefing, a check of what you have brought, and help obtaining a prescribed medicine from a reputable pharmacy or clinic in Kathmandu or Pokhara if you have arrived without it.
- On the trek: guides trained to recognise altitude illness, carrying a pulse oximeter with twice-daily readings above 4,000 m, emergency medication, and oxygen on high passes and peaks.
- After the trek: a check-in before you fly and a clinic appointment arranged if any symptom has not cleared.
Ask us for the altitude profile of any trek before your doctor's appointment — it takes us a few minutes and makes the consultation far more useful.
