Diamox (acetazolamide) is the most commonly used drug for prevention and treatment of altitude sickness — and one of the most controversial in mountain medicine. Some take it “just in case”, others reject the idea of prophylaxis on principle. As the expedition doctor at Everest Base Camp 2022 and a participant in many trips above 4000 m, I see both sides — and in this article I’ll give you concrete acetazolamide dosing for prevention and treatment, explain the mechanism of action (carbonic anhydrase), indications, contraindications, interactions, and side effects.
Dosing in a nutshell
- AMS prevention: 125 mg twice daily starting 24 h before reaching new altitude, continue through the trip or until adapted.
- AMS treatment: 250 mg twice daily until symptoms resolve.
- HACE support (after dexamethasone): 250 mg twice daily.
- Glaucoma treatment (original indication): 250 mg 2–4 times daily.
- Epilepsy (registered indication): 250–1000 mg/day in divided doses.
What is Diamox (acetazolamide) — mechanism of action
Acetazolamide is a carbonic anhydrase inhibitor — an enzyme responsible for carbon dioxide metabolism in the body. Blocking this enzyme in the kidneys increases bicarbonate and water excretion, producing a mild metabolic acidosis. This controlled acidosis “tricks” the respiratory center in the brainstem: the brain receives a signal of insufficient oxygen and orders deeper breathing. The effect: better minute ventilation, higher oxygen saturation, faster acclimatization.
Acetazolamide is sold under the brand name Diamox (USA, international) and Diuramid (Poland, by Polfa Warszawa) — 250 mg tablets. In clinical practice one 250 mg tablet is halved, so AMS dosing is usually ½ tablet (125 mg) twice daily.
Indications for acetazolamide
- Glaucoma treatment — lowers intraocular pressure. This was the original Diamox indication from which the drug’s career began.
- Epilepsy — as an adjunct drug in certain seizure types, especially in children (catamenial epilepsy).
- Acute mountain sickness (AMS) — registered off-label (but widely used; Wilderness Medical Society Guidelines 2019 endorse its use).
- Cardiac/renal edema — rarely today, replaced by newer diuretics.
- Metabolic alkalosis — pH correction.
In mountain medicine acetazolamide is used mainly for prevention and early treatment of AMS (Acute Mountain Sickness). Used prophylactically before the trip, it helps overcome the critical first days of altitude exposure — when the body slowly retunes ventilation and hemoglobin production.
Acetazolamide dosing — concrete numbers
Preventive dose for altitude sickness
125 mg twice daily (morning and evening) — start at least 24 hours before reaching a new, significant altitude and continue until full adaptation (or to the end of the trip at higher altitudes). The 125 mg dose equals ½ of a 250 mg tablet. Acetazolamide shortens acclimatization time and prevents altitude sickness symptoms. If you plan fast altitude gain — e.g. a weekend Mont Blanc attempt — take the first dose 24 hours before the planned climb and continue over subsequent days.
In older recommendations you sometimes see 250 mg twice daily preventively — that’s excessive by current Wilderness Medical Society guidelines. Higher dose doesn’t give better protection, but generates more side effects (paresthesias, taste alteration, diuresis).
Therapeutic dose for AMS symptoms
250 mg twice daily — for developing acute mountain sickness of moderate severity (Lake Louise Score 6–9 points). Continue treatment until symptoms resolve + 24 h, combined with rest at the current altitude (no further ascent). If symptoms persist 48 hours or more despite treatment — descent of 500–1000 m is mandatory. With worsening symptoms (altered consciousness, dyspnea at rest) — discontinue acetazolamide and descend immediately.
Dosing in HACE and HAPE
In high altitude cerebral edema (HACE) first-line drug is dexamethasone (8 mg, then 4 mg every 6 h), with acetazolamide (250 mg twice daily) added as support. In high altitude pulmonary edema (HAPE) first-line is nifedipine, acetazolamide plays an ancillary role. In both cases descent and oxygen are key — drugs are only stabilizers during evacuation.
Dosing in children
In children from 6 years — 2.5 mg/kg body weight twice daily, max 125 mg per dose. Children below 6 require individual evaluation by a pediatric travel/mountain medicine physician — not without reason most organizations don’t recommend high treks (>3500 m) for children below 10–12 years.
Contraindications and warnings
- Sulfa allergy — acetazolamide is structurally related. Cross-reaction in 5–10% of patients.
- Renal insufficiency (creatinine > 2 mg/dl) — drug is renally excreted, accumulates.
- Hepatic insufficiency — especially cirrhosis with encephalopathy.
- Metabolic acidosis — acetazolamide deepens it further (diabetic ketoacidosis, starvation).
- Hyponatremia, hypokalemia — drug worsens electrolyte disturbances.
- Pregnancy and breastfeeding — FDA category C, consider only if necessary.
Warnings and precautions: insulin-dependent diabetes (acetazolamide may affect glycemic control), nephrolithiasis (accelerates stone formation), closed-angle glaucoma (paradoxically may worsen — ophthalmology consult). During prolonged use monitor renal and hepatic function. Acetazolamide overdose manifests as aggravated metabolic acidosis, drowsiness, paresthesias — if concerning symptoms appear check dosing and application and consult a physician.
Acetazolamide side effects
- Paresthesias (tingling in fingers, around the mouth, face) — occurs in 60–90% of patients. Harmless but annoying to some. Resolves after stopping the drug.
- Increased diuresis — passing large amounts of urine, especially in first 2–3 days. You must drink more water (additional 1–2 l/day).
- Taste disturbance — metallic taste, “carbonated drinks taste like soap” (classic symptom). Resolves after stopping.
- Dizziness, fatigue — especially at high altitude where we also feel hypoxia symptoms.
- Nausea — rare, mainly at doses >250 mg twice daily.
- Hypokalemia — potassium supplementation with extended use (>2 weeks).
Serious side effects (rare): Stevens-Johnson syndrome, agranulocytosis, metabolic acidosis, anhedonia syndrome. For skin reactions or systemic symptoms — discontinue the drug and consult a physician.
Acetazolamide drug interactions
- Aspirin (acetylsalicylic acid) — at high doses acetazolamide may worsen metabolic acidosis; at normal doses (75–150 mg) clinically insignificant.
- Digoxin — acetazolamide increases potassium excretion, which can potentiate digoxin toxicity.
- Lithium — acetazolamide may increase lithium excretion, reducing therapeutic concentration.
- Other diuretics (furosemide, hydrochlorothiazide) — effects sum up, increased electrolyte disturbance risk.
- Amphetamine, pseudoephedrine, mefloquine — increased concentration of some drugs in blood serum, toxicity risk.
- Oral antidiabetic drugs — increased hypoglycemia risk (rare but possible). Acetazolamide effects on glycemia can be unpredictable.
- Folic acid — acetazolamide may affect absorption; long-term use consider supplementation.
Dosing individually by indication. Adults and children have different schemes — pediatric doses proportional to body weight. Acetazolamide is contraindicated in severe renal/hepatic failure and sulfa allergy. Optimal effect in AMS prevention is achieved when starting 24 hours before altitude exposure.
My opinion on acetazolamide prophylaxis — an expedition doctor’s view
The preventive use of Diamox from the start of a trip is controversial. In my opinion the best and healthiest acclimatization is natural acclimatization without prophylactic drug use — following the 300–500 m per day ascent rule, with rest days every 1000 m. Pharmacology should be an emergency tool, not a foundation.
However, in people who have experienced severe altitude illness in the past (HAPE, HACE, prior AMS requiring evacuation), prophylaxis with acetazolamide 125 mg twice daily from the start of the trip is recommended and justified. Similarly for people doing “fast trips” (weekend Mont Blanc from airplane) — natural acclimatization is impossible, and pharmacologic prophylaxis saves the trip.
If you take acetazolamide preventively — remember increased diuresis. You drink 2–4 l of water + additional 1–2 l = total 3–6 l/day. You need a strategy for frequent night bathroom trips (container in the tent), because leaving a warm sleeping bag at -20°C risks hypothermia and frostbite. That’s not a joke, it’s practical advice that consultants often forget.
Frequently asked questions
How does Diamox work?
Diamox (acetazolamide) is a carbonic anhydrase inhibitor — an enzyme metabolizing carbon dioxide. It blocks carbonic anhydrase in the kidneys, causing increased bicarbonate excretion and mild metabolic acidosis. Acidosis stimulates the respiratory center in the brainstem, leading to deeper breathing, higher oxygen saturation, and faster acclimatization. Additionally, acetazolamide lowers intraocular pressure (hence use in glaucoma) and stabilizes neuronal membranes (hence use in epilepsy).
How to take Diamox for altitude sickness?
For altitude sickness prevention: 125 mg (½ of a 250 mg tablet) twice daily — morning and evening. Start 24 h before reaching new altitude and continue through the trip or until full adaptation. For AMS treatment (Lake Louise Score 6–9 points): 250 mg twice daily, until symptoms resolve + 24 h. While taking, increase water intake by 1–2 l daily — acetazolamide is a diuretic. Prefer taking after food to limit stomach discomfort.
How long can you take Diamox?
In mountain medicine acetazolamide is typically used for 7–14 days — covering the key acclimatization days at altitude. In chronic use (e.g. glaucoma) it can be administered for months, but requires monitoring — electrolyte, creatinine, and acidosis checks every 1–2 weeks. On expeditions over 2–3 weeks of continuous use consider potassium supplementation. After returning from the mountains the drug can be stopped without dose reduction — no dependency.
Can you take Diamox on an empty stomach?
Diamox (acetazolamide) can be taken both on empty stomach and with food — but most patients tolerate it better after eating, as it reduces stomach discomfort and nausea risk. In expedition practice the morning dose is taken after breakfast (around 7–8 AM) and the evening dose after dinner (around 6–7 PM). Avoid taking immediately before sleep — diuresis may wake you for a bathroom trip.
Does Diamox cause side effects?
Yes, the most common side effects at doses used in mountain medicine (125–500 mg/day) are: tingling of fingers and around the mouth (paresthesias) in 60–90% of patients, increased diuresis, taste disturbance (metallic taste, carbonated drinks taste ”different”), dizziness, fatigue, rarely nausea. Side effects are usually mild and resolve after discontinuation. Rare serious reactions (Stevens-Johnson syndrome, agranulocytosis) occur in <0.1% and require immediate discontinuation and medical consultation.
Sources
- Luks AM, Auerbach PS, Freer L, et al. Wilderness Medical Society Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2019 Update. Wilderness Environ Med. 2019;30(4S):S3-S18.
- Ward M, Milledge JS, West JB. High Altitude Medicine and Physiology, 5th edition. CRC Press — chapter on AMS pharmacology.
- Hidalgo J. et al. High Altitude Medicine: A Case-Based Approach. Springer, 2023 — clinical cases of acetazolamide.
- Auerbach PS (ed.). Wilderness Medicine, 7th edition. Elsevier, 2016 — chapter “Pharmacology of High Altitude”.
- Leaf DE, Goldfarb DS. Mechanisms of action of acetazolamide in the prophylaxis and treatment of acute mountain sickness. J Appl Physiol. 2007;102(4):1313-22.
Medical disclaimer: Acetazolamide (Diamox/Diuramid) is a prescription drug. Do not use without consultation from a travel/mountain medicine physician. This article is educational and does not replace individual health assessment. In a life-threatening situation on expedition — call local emergency services.