How do I prevent altitude sickness?

The single most effective prevention is boring: go up slowly. Altitude illness comes from low oxygen at elevation, and the CDC puts the risk zone starting around 8,000 feet. Your body can adapt - that is acclimatization - but only on its own schedule, not yours. The CDC's practical rules: spend two to three nights around 8,000 to 9,000 feet before going higher, because that is markedly protective against acute mountain sickness. Once above 9,000 feet, raise your sleeping altitude by no more than about 1,600 feet per day, and take an extra rest day for every 3,300 feet gained. The altitude you sleep at matters more than the altitude you visit during the day. For the first 48 hours at elevation: no alcohol, only mild exercise, and keep your usual caffeine if you are a regular user, so withdrawal headache does not mimic altitude headache. If an abrupt ascent is unavoidable - flying straight to a high city like La Paz or Cusco - the CDC suggests considering acetazolamide, a prescription medication that speeds acclimatization. A travel clinician or telehealth travel consult can sort out whether you need it. Know the danger signs: headache plus nausea, dizziness, or fatigue means stop ascending. Worsening symptoms, confusion, or breathlessness at rest mean descend now. Pymander is a free AI doctor, 24/7 by text. It can help you plan an ascent schedule for your itinerary and recognize warning symptoms.