What Is Altitude Sickness and Why Every Nepal Trekker Must Understand It
Altitude sickness is the single biggest health risk on Nepal's high treks — more dangerous than cold, terrain, or fitness. It can affect anyone above 2,500m regardless of age or fitness, and in its severe forms it kills. The good news is that it's largely preventable with the right knowledge and pacing. This guide explains the symptoms, the golden rules of acclimatisation, the role of Diamox, and — most importantly — when to descend. This article is general information, not medical advice; always consult a doctor before your trek and a medical professional if you develop symptoms.
The Three Forms of Altitude Sickness
| Type | What It Is | Severity |
|---|---|---|
| AMS | Acute Mountain Sickness | Mild — common, manageable |
| HACE | High-Altitude Cerebral Edema | Severe — fatal if untreated |
| HAPE | High-Altitude Pulmonary Edema | Severe — fatal if untreated |
AMS is common and usually mild. HACE and HAPE are medical emergencies where immediate descent is the only proven cure.
What Are the Symptoms of Altitude Sickness?
AMS symptoms typically appear above 2,500m, often within hours of arriving at a new altitude.
- Headache (the hallmark symptom)
- Nausea or vomiting
- Fatigue and weakness
- Dizziness
- Sleep disturbance and loss of appetite
Danger signs (HACE/HAPE — descend immediately): confusion, loss of coordination (unable to walk a straight line), breathlessness at rest, persistent cough, or a gurgling chest.
The Golden Rules of Acclimatisation
Prevention is overwhelmingly about pacing. Follow these rules above 3,000m:
- Sleep low: Gain no more than 300–500m of sleeping altitude per night
- Rest days: Take an acclimatisation day every 1,000m of elevation gained
- Climb high, sleep low: Day-hike higher, then return to sleep lower
- Hydrate: Drink 3–4 litres of water daily
- No alcohol: Avoid alcohol and sleeping pills at altitude
- Eat carbs: Carbohydrates help your body cope with thin air
Diamox (Acetazolamide): What You Should Know
Diamox is the standard preventive medication for AMS. A systematic review and meta-analysis found acetazolamide prophylaxis was associated with a roughly 48% relative-risk reduction in AMS compared to placebo.
- Typical preventive dose: 125mg twice daily, starting 1–2 days before reaching 3,500m, continuing 48 hours after maximum altitude
- Side effects: Tingling fingers, frequent urination, altered taste of fizzy drinks
- Availability: Sold in Kathmandu pharmacies (locally branded versions exist)
- Important: Diamox aids acclimatisation — it does not let you ascend faster or replace descent if you're sick. Consult your doctor for dosing.
Treatment: When to Descend
- Mild AMS: Stop ascending, rest, hydrate; do not go higher until symptoms clear
- Symptoms worsen overnight: Descend
- HACE/HAPE signs: Descend immediately — this is the only cure. Emergency medications (dexamethasone for HACE, nifedipine for HAPE) buy time but don't replace descent
- Never ascend with symptoms: The cardinal rule of altitude trekking
Cold worsens how your body copes at altitude, so a warm sleeping bag and proper down jacket indirectly support safe acclimatisation. Helicopter evacuation can cost USD 3,000–10,000+, so insurance with high-altitude rescue cover is essential.
Frequently Asked Questions
What altitude does altitude sickness start?
Altitude sickness can begin above 2,500m. The risk rises significantly above 3,000m, which is why the golden rules of acclimatisation — limited daily sleeping-altitude gain and rest days — apply on all of Nepal's high treks.
Should I take Diamox for Everest Base Camp?
Many trekkers take Diamox prophylactically for EBC (typically 125mg twice daily, started before 3,500m), and research shows it reduces AMS risk. However, you should consult your doctor before your trek — Diamox has side effects and isn't a substitute for proper acclimatisation.
What are the first signs of altitude sickness?
The first and hallmark sign is a headache, often with nausea, fatigue, dizziness, and disturbed sleep. If you develop these above 2,500m, stop ascending, rest, and hydrate. Confusion, loss of coordination, or breathlessness at rest are emergencies requiring immediate descent.
How long does it take to acclimatise to high altitude?
Acclimatisation is gradual — your body needs roughly a rest day for every 1,000m gained above 3,000m, and full adaptation takes several days. There's no way to rush it; slow ascent and built-in acclimatisation days are the only reliable approach.
This article is general information only and not a substitute for professional medical advice. Consult a doctor before trekking at altitude and seek medical help if symptoms develop.
Trek Warm and Safe with Gear from Himalayan Hardwear, Thamel
Warmth supports acclimatisation — get proper sleeping bags and down jackets at our store in Jyatha, Thamel, Kathmandu. Open daily 9am–8pm, or contact us on +977-1-5362200.
