Altitude Sickness · Acetazolamide timing
Start Diamox (acetazolamide) about one day (24 hours) before you begin your ascent, and continue it through ascent and the prescribed acclimatization period at your target sleeping altitude. Starting it the day before gives it time to help your body acclimatize as you go up.
| Stage | What to do |
|---|---|
| 1 day before ascent | Start acetazolamide |
| During ascent | Keep taking it as you go up |
| After reaching target sleeping altitude | Often 2 days after a gradual ascent; a rapid ascent can need longer. Follow your prescribed plan. |
| Still climbing higher? | Continue until you reach your highest sleeping elevation and have stayed a couple of days |
| Heading back down | Your clinician sets the stop plan; do not stop while continuing to ascend |
The exact dose and schedule are set during your visit, but the pattern is the same: begin the day before, cover the climb, and continue through the first couple of days at your target height.
Starting prescribed prevention on the day of ascent can still help, according to WMS guidance. Follow the plan your clinician gave you rather than taking extra doses to catch up. If symptoms have already started, stop ascending and seek advice; prevention and treatment are different plans. Do not use acetazolamide to delay descent or emergency care.
Because you start it the day before you ascend, request acetazolamide online a few days before your trip so the prescription is filled and packed.
A $45 asynchronous visit (no video, no membership) for adults in eligible states, reviewed by a licensed clinician. Tell us your destination and how fast you ascend, and we tailor the timing to your trip.
Start acetazolamide (Diamox) about one day (24 hours) before you begin your ascent to altitude. Starting it the day before gives it time to help your body acclimatize as you go up.
The stop date depends on your ascent and sleeping altitude. WMS guidance commonly continues prevention for two days at the target altitude after a gradual ascent, and sometimes longer after rapid ascent. If you keep ascending, do not automatically stop after two days. Confirm the plan with your prescriber.
Starting prescribed prevention on the day of ascent can still help. Follow your clinician’s instructions; do not double doses. New altitude symptoms need assessment and a pause in ascent, and severe symptoms need descent and emergency care. Do not assume a prevention dose treats an established illness.
Yes. Bidwell Health offers a $45 asynchronous online visit, no video and no subscription, for adults in eligible states. A licensed clinician reviews your trip and sends acetazolamide to your pharmacy when clinically appropriate, so you can start it the day before you ascend.
Plan around sleeping altitude, not just the highest viewpoint. Tell your clinician where you sleep each night, how quickly you ascend and any previous altitude illness. A brief cable-car visit is different from sleeping high. Build in acclimatization days; medicine does not make a rapid ascent safe. Drink normally rather than forcing extra water. CDC altitude guidance.
Do not climb higher with symptoms of altitude illness. Stop ascending if headache with nausea, dizziness or unusual fatigue develops after ascent. Descend if symptoms worsen or fail to improve. Confusion, trouble walking, or breathlessness at rest requires immediate descent, emergency help and oxygen when available; do not wait for a pill to work. Wilderness Medical Society guidance.
CDC Yellow Book: high-altitude travel · Wilderness Medical Society 2024 guidance