Diamox for Altitude Sickness: Dosage, Side Effects & When to Start
For most adults, the prevention dose of Diamox (acetazolamide) is 125 mg every 12 hours. Start it the day before you go up, and keep taking it for your first 2 days at your highest sleeping altitude, longer if you keep climbing. In a 2012 meta-analysis, acetazolamide lowered the relative risk of acute mountain sickness by 48% compared with placebo. Our clinical team recommends it if you'll sleep above about 2,750 m (9,000 ft) on your first night, or if you've had altitude sickness before. Start your visit on Wandr and our providers can send a prescription to your local pharmacy before your trip.
For most adults, the prevention dose of Diamox (acetazolamide) is 125 mg every 12 hours. Start it the day before you go up, and keep taking it for your first 2 days at your highest sleeping altitude, longer if you keep climbing. In a 2012 meta-analysis, acetazolamide lowered the relative risk of acute mountain sickness by 48% compared with placebo. Our clinical team recommends it if you'll sleep above about 2,750 m (9,000 ft) on your first night, or if you've had altitude sickness before. Start your visit on Wandr and our providers can send a prescription to your local pharmacy before your trip.
Last updated October 31, 2026 by Alec Freling, MD
What Is Diamox and How Does It Work?
Diamox is the brand name for acetazolamide, a prescription carbonic anhydrase inhibitor. It makes your blood slightly more acidic, which prompts you to breathe faster and deeper. That extra breathing raises your oxygen level and speeds up the acclimatization your body would do anyway (NCBI Bookshelf NBK532282).
In a 2012 meta-analysis in the Journal of Travel Medicine, acetazolamide lowered the relative risk of acute mountain sickness (AMS) by 48% compared with placebo (PubMed 22943270). That means about half the risk, not protection for 48% of travelers. The same review found 250 mg a day worked about as well as higher doses with fewer side effects. A 2021 review of 22 randomized trials also found that 125, 250 and 375 mg twice daily all reduced AMS compared with placebo (PMC8588948).
Diamox Dosage for Altitude Sickness Prevention
Preventive (Prophylactic) Dosing
Who | Dose | How often |
|---|---|---|
Most adults | 125 mg | Every 12 hours |
Adults over 100 kg (220 lb) | 250 mg | Every 12 hours |
The lower dose works for most travelers and causes less tingling. Higher doses don't prevent AMS any better for most people.
Treatment Dosing (If Symptoms Start)
For mild AMS, the adult treatment dose is 250 mg every 12 hours. Stop climbing until symptoms go away. If symptoms get worse despite rest and medication, go down. Descent is the most reliable treatment.
When to Start Taking Diamox Before Your Trip
Start the day before you go up. If you forget, starting on the day of ascent still helps (Am Fam Physician).
Keep taking it for your first 2 days at your highest sleeping altitude. If you keep climbing, as on a trek, continue until you stop gaining altitude or start heading down.
Common Side Effects of Diamox
Most side effects are mild and stop when you stop the medicine:
- Tingling in the fingers, toes or face (the most common, and less likely at 125 mg)
- Needing to urinate more often
- Fizzy drinks tasting flat or metallic
- Mild nausea or tiredness
Get medical help for a rash, trouble breathing, or swelling of the face or throat.
Who Should NOT Take Diamox
- Anyone with a past anaphylaxis or Stevens-Johnson syndrome from a sulfonamide drug
- People with severe kidney or liver disease, or low sodium or potassium levels
- Anyone who is pregnant or breastfeeding, unless their own clinician advises it
A sulfa antibiotic allergy alone usually isn't a reason to avoid acetazolamide. The CDC notes no reported cross-reaction between the two. Tell your clinician about any drug allergy, especially if you have several.
Do You Actually Need Diamox? A Risk-Based Approach
The CDC sorts travelers starting from below 1,200 m (4,000 ft) into three risk levels:
Risk | Your history | Where you sleep on night 1 | How fast you climb above 3,000 m (9,800 ft) | Diamox? |
|---|---|---|---|---|
Low | No AMS, or only mild AMS | Below 2,750 m (9,000 ft) | Less than 500 m (1,650 ft) a day | Not needed; carry it in case |
Medium | Moderate to severe AMS before | 2,750 to 3,400 m (9,000 to 11,150 ft) | More than 500 m a day, with rest days | Worth considering |
High | Past HAPE or HACE | Above 3,400 m (11,150 ft) | More than 500 m a day, without rest days | Strongly recommended |
Flying straight into Cusco, Peru, puts most travelers at medium to high risk, because the city sits at about 3,400 m (11,150 ft). Machu Picchu itself is lower, at about 2,430 m (7,970 ft). For a full Peru breakdown, see Do you need Diamox for Cusco and Machu Picchu?
How to Get Diamox for Your Trip
Acetazolamide needs a prescription in the US. With Wandr, you start an online visit, answer a short health questionnaire, and a licensed clinician sends the prescription to your local pharmacy if it's right for you. You pay the pharmacy for the medication.
If you can't take acetazolamide, ibuprofen 600 mg every 8 hours also lowers the risk of AMS, though less well. Some travelers also carry dexamethasone for emergencies; it isn't offered through Wandr, so ask your own doctor if your trip calls for it.
Other Tips for Preventing Altitude Sickness
- Climb slowly: above 3,000 m, raise your sleeping altitude by no more than 500 m (1,650 ft) a night
- Take a rest day every 3 to 4 days, or for every 1,000 m you gain
- Don't go higher while you have symptoms
- Go down if symptoms get worse, or if you're confused, unsteady or short of breath at rest
- Go easy on alcohol for your first couple of days up high
Looking to get Diamox prescribed to your local pharmacy for just $89? Order today with Wandr
Frequently Asked Questions About Diamox and Altitude Sickness
How long before altitude should I start taking Diamox?
Start the day before you go up. Starting the same day still gives some protection.
What is the best Diamox dosage for altitude sickness prevention?
For most adults, 125 mg every 12 hours. Adults over 100 kg may take 250 mg every 12 hours.
Can I take Diamox if I have a sulfa allergy?
Usually yes, if the allergy is to sulfa antibiotics. Avoid it if you've had anaphylaxis or Stevens-Johnson syndrome from a sulfonamide, and tell your clinician about any drug allergies.
Does Diamox have interactions with other medications?
Yes. Tell your clinician about everything you take, especially high-dose aspirin and topiramate.
Will Diamox make me feel tired or affect my performance at altitude?
Some people feel mildly tired or tingly. Most find it helps them feel better at altitude, because it speeds acclimatization.
Do I need Diamox for Cusco, Peru?
Most travelers flying straight into Cusco fall into the CDC's medium or high risk group, so it's worth considering. Starting lower, in the Sacred Valley, lowers the risk.
Is Diamox safe to take while trekking or exercising at altitude?
Yes, for most people. Drink enough water, since it makes you urinate more, and keep climbing slowly.
How long can I take Diamox?
Usually only for your first 2 days at your highest altitude, or until you stop climbing. Ask your clinician about longer trips.
Medical disclaimer: This article is for informational purposes only and does not replace professional medical advice. Start your visit on Wandr to consult with our providers before starting any medication, including acetazolamide. If you experience severe altitude sickness symptoms (confusion, difficulty walking, severe shortness of breath at rest), descend immediately and seek emergency medical care.
Sources
- CDC Yellow Book 2026 — High-Altitude Travel and Altitude Illness. cdc.gov
- Acetazolamide — StatPearls, NCBI Bookshelf. ncbi.nlm.nih.gov
- Acetazolamide for the prevention of acute mountain sickness, Journal of Travel Medicine (2012). PubMed 22943270
- Efficacy of acetazolamide for AMS prophylaxis: Systematic review, meta-analysis, and trial sequential analysis of randomized clinical trials (2021). PMC8588948
- Armstrong, Acute Altitude Illness: Updated Prevention and Treatment Guidelines from the Wilderness Medical Society, American Family Physician (2020). aafp.org
- Identifying the lowest effective dose of acetazolamide for AMS prophylaxis: Systematic review and meta-analysis. NCBI NBK109621
- Acetazolamide pre-treatment before ascending to high altitudes: When to start? High Altitude Medicine & Biology (2014). PMC4276215
- Reduced Acetazolamide Dosing in Countering Altitude Illness (RADICAL Trial). PubMed 30630671
Alec Freling, MD is a board-certified emergency medicine physician and co-founder of Wandr Health with ER experience treating returning travelers.