Altitude sickness guide
Altitude sickness (AMS — acute mountain sickness) affects 25-50% of travelers above 2,500m. Knowledge of prevention + recognition can save your life.
Altitude tiers
- Up to 2,400m (8,000 ft): Minimal risk. Some mild fatigue possible on day 1.
- 2,400-3,500m: Moderate altitude. AMS in 25-30% of travelers. Acclimatize 1 day.
- 3,500-5,500m: High altitude. AMS in 40-50%. Acclimatize 2-3 days per major elevation jump.
- Above 5,500m: Extreme altitude. Severe AMS, HACE, HAPE risk. Climbing-skill territory.
Prevention rules
- Climb high, sleep low. Daytime exertion at altitude OK; sleeping at lower altitude helps.
- Hydrate 3-4× normal. Dehydration mimics altitude sickness + worsens it.
- No alcohol for first 48h. Sleep medications too.
- Diamox (acetazolamide) 125-250 mg twice daily, starting 24h before ascent. Prescription only.
- Coca tea / leaves in Andean countries has mild benefits + local culture.
- Ascend gradually: max 300-500m sleep elevation gain per day above 3,000m.
Recognize the symptoms
Mild AMS (treat with rest, hydration, sometimes Diamox)
- Headache (most common — like a hangover)
- Nausea, loss of appetite
- Fatigue, dizziness
- Sleep disturbance
⚠ Severe AMS / HAPE / HACE (DESCEND IMMEDIATELY + medical help)
- Severe headache not responding to ibuprofen
- Vomiting (not just nausea)
- Shortness of breath at rest
- Confusion, ataxia (can't walk straight)
- Persistent dry cough turning to wet
- Cyanosis (blue lips/fingers)
HACE (cerebral edema) + HAPE (pulmonary edema) are life-threatening. Treatment is immediate descent. Don't try to "push through."
Common altitude destinations
Lhasa, Tibet (3,656 m)
Risk: High
Acclimatize 2-3 days. Diamox prescribed before departure.
Cusco, Peru (3,400 m)
Risk: High
Don't go straight to Cusco from sea level. Coca tea helps.
La Paz, Bolivia (3,640 m)
Risk: High
World's highest capital. Take it slow day 1.
Lake Titicaca (3,810 m)
Risk: High
Cusco acclimatization helps before going here.
Quito, Ecuador (2,850 m)
Risk: Moderate
Most travelers tolerate. Hydrate.
Bogotá, Colombia (2,640 m)
Risk: Moderate
Most travelers tolerate without issue.
Mexico City (2,240 m)
Risk: Mild
Some travelers feel sluggish day 1.
Aspen + Vail + Breckenridge (USA, 2,400-2,900 m)
Risk: Moderate
Ski-resort sickness common — drink water + go easy day 1.
Mt Fuji summit (3,776 m)
Risk: High
Climb routes overnight stays at 8th station help.
Mt Kilimanjaro (5,895 m)
Risk: Severe
8-9 day routes much higher success rate than 5 day.
Everest Base Camp (5,364 m)
Risk: Severe
Trek takes 11-12 days for proper acclimatization.
Annapurna Circuit Thorong La Pass (5,416 m)
Risk: Severe
Two weeks to circuit. Diamox common.
Atacama Desert + San Pedro (2,400 m)
Risk: Moderate
Many travelers OK but plan rest day.
Yellowstone (2,500m+ in places)
Risk: Mild
Tour-related stops moderate.