Altitude sickness (Acute Mountain Sickness, or AMS) is the single most common reason trekkers turn back early in Nepal. The good news: with the right strategy, it is almost entirely preventable.
- 25–30% of trekkers experience mild AMS above 3,000 m
- Most cases are fully preventable with proper acclimatisation
- 0 m descent is always the most effective treatment for severe AMS
What Is Altitude Sickness?
As you ascend, atmospheric pressure drops and with it the partial pressure of oxygen. Your body responds by breathing faster, producing more red blood cells, and adjusting kidney function. AMS occurs when you ascend faster than your body can adapt — typically above 2,500 m.
AMS exists on a spectrum from mild to life-threatening. Understanding the stages is critical for every trekker.
Recognising the Symptoms
Mild AMS (Manageable)
Mild AMS typically appears 6–12 hours after arriving at a new altitude. Common signs include:
- Headache (the most common symptom)
- Fatigue and weakness
- Dizziness or light-headedness
- Loss of appetite, nausea
- Difficulty sleeping
With mild AMS: stop ascending, rest at your current altitude, hydrate, and take ibuprofen for the headache. Do not go higher until symptoms fully resolve (usually 24–48 hours).
Moderate to Severe AMS — Descend Immediately
The 7 Rules of Acclimatisation
Follow these rules and your chances of developing serious AMS drop dramatically:
- 1 Ascend slowly. Above 3,000 m, gain no more than 300–500 m of sleeping altitude per day
- 2 Rest days matter. For every 3 days of ascent, take 1 full rest day (EBC itinerary includes acclimatisation days at Namche and Dingboche for a reason)
- 3 Climb high, sleep low. Day hikes to higher altitude, then return to sleep lower down, are highly effective
- 4 Hydrate aggressively. Drink 3–4 litres of water per day. Dehydration masks and worsens AMS symptoms
- 5 Avoid alcohol and sedatives. Both suppress respiration, worsening oxygen desaturation at night
- 6 Eat carbohydrates. A high-carb diet is metabolically more oxygen-efficient than fat or protein at altitude
- 7 Never ignore symptoms. Tell your guide. They are trained to help, not to judge you
Diamox (Acetazolamide): Should You Take It?
Diamox is a prescription medication that accelerates acclimatisation by stimulating deeper breathing. It is effective and widely used, but it is not a substitute for proper acclimatisation — think of it as insurance, not a shortcut.
The standard prophylactic dose is 125 mg twice daily, starting 24 hours before ascent above 3,000 m. Common side effects include tingling in the fingers, increased urination, and altered taste of carbonated drinks. Diamox is a sulfa drug — do not take it if you are allergic to sulfonamides.
Always consult a physician before taking Diamox.
Insurance & Evacuation
Travel insurance that specifically covers high-altitude trekking and emergency helicopter evacuation is non-negotiable. Helicopter evacuations from Everest Base Camp can cost USD 5,000–15,000. Most trekking agencies (including TerraBlaze) will not allow trekkers above 4,000 m without proof of insurance covering evacuation.
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