Acetazolamide (Diamox) for Altitude Sickness
Acetazolamide is the prescription pill travellers take to prevent acute mountain sickness when they will sleep above about 8,000 ft (2,500 m) faster than the body can adapt. It speeds acclimatization rather than masking symptoms. The usual preventive dose starts the day before ascent and continues for two days at your highest altitude.
Also known as: Diamox
Availability
Prescription only
Start
The day before ascent
Course
Until 2 days at your highest sleeping altitude
Typical cost
Generic, usually under $20 for a trip supply
Who needs it
- Travellers flying or driving directly to high cities: Cusco (11,150 ft), La Paz (11,940 ft), Lhasa (11,990 ft), Quito (9,350 ft), Leh (11,480 ft)
- Trekkers and climbers who will ascend faster than the recommended 1,600 ft (500 m) per day above 10,000 ft (3,000 m), such as Kilimanjaro or Everest Base Camp itineraries
- Anyone who has had altitude sickness before and is returning to a similar altitude
- Travellers who cannot build extra acclimatization days into the trip
How it works
Acetazolamide makes the kidneys excrete bicarbonate, which slightly acidifies the blood. That nudges the body to breathe more, especially during sleep, which raises blood oxygen and mimics the natural acclimatization process. Because it treats the cause rather than the headache, it is the CDC's preferred preventive medication for altitude illness.
How it's taken
The standard CDC summary. Your pharmacist confirms the schedule for your itinerary and health history.
- 1Prevention: the standard adult dose is 125 mg twice a day, starting the day before you ascend and continuing until you have spent two nights at your highest sleeping altitude, or until you start descending
- 2Some clinicians use 250 mg twice daily for very rapid ascents or heavier travellers; your pharmacist confirms the right dose for your itinerary
- 3It works alongside, not instead of, a sensible ascent: above 10,000 ft, sleep no more than about 1,600 ft higher each night and take a rest day every 3–4 days
- 4If symptoms of altitude sickness appear anyway (headache plus nausea, dizziness, poor sleep), do not go higher until they resolve; descend if they worsen
Side effects and who should not take it
Common side effects
- Tingling in the fingers, toes and around the mouth (very common and harmless)
- Carbonated drinks taste flat or metallic
- Passing urine more often, so drink to thirst
- Occasionally drowsiness, nausea or blurred vision
Talk to the pharmacist first if
- People with a history of a serious allergic reaction to sulfonamide (“sulfa”) antibiotics. The cross-reaction risk is low but the drug is usually avoided in this group
- Significant kidney or liver disease, or low potassium or sodium
- Pregnant travellers should discuss the risks with their clinician
- Travellers already taking high-dose aspirin or certain glaucoma medications need a medication review first
Alternatives
Gradual ascent
The most effective prevention. Adding one or two acclimatization nights at an intermediate altitude often removes the need for medication.
Dexamethasone
A steroid that relieves symptoms but does not speed acclimatization. Used for prevention only in specific situations, such as rescue flights to very high altitude, or when acetazolamide cannot be taken.
Ibuprofen
Some evidence for preventing altitude headache; weaker than acetazolamide for preventing acute mountain sickness overall.
How to get it in California
Voyax Health consultations are available to California residents.
Enter your destinations on Voyax Health. The trip planner records each stop's elevation, and your health brief flags stops where acetazolamide is worth discussing.
A licensed pharmacist reviews your health history and itinerary and, where appropriate, a prescription is issued and sent to your California pharmacy. Generic acetazolamide is inexpensive and widely stocked.
Start the course the day before you go up, so pick up the prescription before you fly.
Frequently asked questions
Do I need a prescription for acetazolamide in the US?▼
Yes. Acetazolamide (Diamox) is prescription-only in the United States. Voyax Health's pharmacist review can result in a prescription sent to your California pharmacy when it is appropriate for your trip.
Do I need altitude sickness pills for Cusco and Machu Picchu?▼
Cusco sits at about 11,150 ft (3,400 m), high enough that many visitors who fly in directly get symptoms in the first day or two. Acetazolamide started the day before arrival is commonly recommended, especially if you cannot spend a night lower in the Sacred Valley first. Machu Picchu itself is lower (about 7,970 ft).
Does acetazolamide mask the symptoms of altitude sickness?▼
No, and that is the point. Unlike painkillers, it speeds up acclimatization. If you develop symptoms despite taking it, treat them as real: stop ascending and descend if they get worse.
Can I take acetazolamide if I am allergic to sulfa drugs?▼
It is usually avoided after a serious reaction to a sulfonamide antibiotic, even though the chemistry differs and true cross-reactions are uncommon. Tell your pharmacist about any sulfa allergy so an alternative plan can be made.
Destinations where this matters
Country guides where this vaccine or medication is commonly part of the plan.
PeruModerate riskPeru carries a CDC Level 1 travel health notice. Malaria risk exists in areas below 2,500m elevation east of the Andes. Key travel vaccines: COVID-19, Hepatitis A, Hepatitis B.
BoliviaModerate riskBolivia carries a CDC Level 2 travel health notice. Malaria risk exists in areas below 2,500m elevation. Key travel vaccines: COVID-19, Chikungunya, Hepatitis A. Required for entry (applies below 2300m)
NepalModerate riskNepal carries a CDC Level 1 travel health notice. Malaria risk exists in certain areas of Nepal below 2,000m elevation. Key travel vaccines: COVID-19, Hepatitis A, Hepatitis B. Yellow fever vaccine is not needed for disease protection in Nepal. However, it's required for entry if you're coming from a country with yellow fever risk, including airport layovers over 12 hours.
TanzaniaHigh riskTanzania carries a CDC Level 2 travel health notice. Malaria risk exists in all areas of Tanzania below 1,800 meters (5,900 feet) elevation. Key travel vaccines: COVID-19, Hepatitis A, Hepatitis B.
EcuadorModerate riskEcuador carries a CDC Level 1 travel health notice. Malaria risk exists in certain provinces below 5,000 feet elevation. Key travel vaccines: COVID-19, Hepatitis A, Hepatitis B. Required for entry (applies below 2300m)
ChinaLow riskChina carries a CDC Level 1 travel health notice. No malaria risk. Key travel vaccines: COVID-19, Hepatitis A, Hepatitis B.
Get it prescribed for your trip
Enter your destinations and dates. Your free health brief shows whether acute mountain sickness (altitude sickness) is a risk on your route; a licensed pharmacist then reviews your plan for $39.99 per traveller and sends prescriptions to your pharmacy.
Start my free health briefConsultations are available to California residents. Vaccines and medications are paid at your pharmacy.
Sources: CDC Yellow Book — High Elevation Travel & Altitude Illness. Last updated 2026-09-28. This page is informational and not a substitute for advice from a pharmacist or travel-medicine provider.