Going up to a high plateau, climb by sleeping altitude (how high you sleep that night) and go down if symptoms get worse; don't tough it out

High value
Evidence A
Buys life
Free
Takes some hours
Some willpower

In a real emergency, call 911 first, then read this.

In plain words

What counts is how high you sleep, not how high you went during the day. Sleeping above 2,450 meters carries a risk of altitude sickness. Above 3,000 meters, raise the altitude you sleep at by no more than 500 meters per night, and allow one extra day for acclimatization for every 1,000 meters gained. If you get a headache with nausea, an unsteady walk, a change in consciousness, or shortness of breath even at rest, go down. Going down comes before oxygen and medicine.

Cost: One or two extra days for acclimatization. Preventive medicine is prescription-only, so ask a doctor before you leave. The hard part is being willing to keep these days free when the schedule is tight.
What you get: Sleeping above 2,450 meters carries a risk of altitude sickness. High-altitude cerebral edema and pulmonary edema (fluid in the brain and lungs) can kill if you don't descend to lower ground in time
Notes: What counts is "how high you sleep," not how high you went during the day. A headache with nausea, an unsteady walk, a change in consciousness, or shortness of breath even at rest are all signs to go down. Going down comes before oxygen and medicine, and continuing upward while on oxygen is wrong.
Evidence grade: A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.
Sources: 美国疾病控制与预防中心. 黄皮书·高海拔旅行与高原病：「Any unacclimatized traveler proceeding to a sleeping altitude of ≥2,450 m (≥8,000 ft)—and sometimes lower—is at risk for altitude illness」
上升速度「500 m (1,650 ft) per night in sleeping altitude once above 3,000 m (9,800 ft)」，每上升 1000 米加一天适应日
乙酰唑胺预防「125 mg twice a day; 250 mg twice a day if >100 kg body weight」
「If symptoms become worse despite rest or treatment at the same elevation」必须下撤. https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html
荒野医学会 (2024). 急性高原病预防、诊断与治疗临床实践指南（2024 更新）. Wilderness & Environmental Medicine. https://doi.org/10.1016/j.wem.2023.05.013

Translated from the Chinese original. Original book, section 13, tip 33. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer