Altitude sickness prevention for Indian trekkers — a practical guide
By Kavya Menon (Kavya Menon covers adventure and outdoor travel for Indian travellers — scuba diving, trekking, safaris, paragliding, skiing and rafting — with a focus on permits, seasons, gear and safety for trips abroad and across India.) · Published · 10 min read
A practical, medically grounded guide to preventing altitude sickness on Himalayan and overseas treks, including the acclimatisation rules, Diamox basics and the descent decisions that save lives.
Quick answer
Prevent altitude sickness by ascending slowly, not flying straight to high altitude, and following the climb-high-sleep-low rule. Above about 3,000m, limit your daily sleeping-altitude gain to roughly 300 to 500m and add a rest day every 600 to 1,000m. Diamox (acetazolamide) helps if you must ascend fast or have a history of it. If symptoms worsen, the only reliable cure is to descend. This is general guidance, not a substitute for a doctor.
What altitude sickness actually is
Acute mountain sickness (AMS) happens because air pressure, and therefore available oxygen, drops as you climb. Your body needs time to adapt, and if you outrun that adaptation, fluid shifts and low oxygen produce symptoms. It typically begins above 2,500 to 3,000m.
Mild AMS feels like a hangover: headache, nausea, loss of appetite, fatigue and poor sleep. The danger is the two severe forms. High-altitude cerebral oedema (HACE) is swelling of the brain, marked by confusion, loss of coordination (a staggering, drunken walk) and drowsiness. High-altitude pulmonary oedema (HAPE) is fluid in the lungs, marked by breathlessness at rest, a wet cough and extreme fatigue. Both are medical emergencies that can kill within hours if ignored.
Indian trekkers are exposed to this on popular routes such as Leh-Ladakh (where you can fly straight to 3,500m), Everest Base Camp, Annapurna, Kedarnath, Hampta Pass, Stok Kangri and Kilimanjaro, all of which sit in the AMS zone.
The acclimatisation protocol
Acclimatisation is the single most effective prevention, and it is free. The governing principle is gradual gain in sleeping altitude, because it is the altitude you sleep at, not the highest point you touch during the day, that drives AMS.
- Above ~3,000m, cap your sleeping-altitude gain at roughly 300 to 500m per night.
- Build in a rest day for every 600 to 1,000m of net ascent, ideally spending it doing a short higher day-hike.
- Climb high, sleep low: hiking to a higher point during the day and returning to a lower camp to sleep speeds adaptation.
- Hydrate well and avoid alcohol and sleeping pills, which suppress breathing and worsen night-time oxygen levels.
The most common Indian mistake is flying into Leh and immediately sightseeing or pushing to higher passes. Spend the first 24 to 48 hours resting at Leh altitude before going higher.
Recognising the warning signs early
Learn to read symptoms honestly, because denial is dangerous at altitude. Treat any new headache above 2,500m as possible AMS until proven otherwise. Mild AMS (headache plus one of nausea, fatigue, dizziness or poor sleep) means stop ascending. Do not go higher to sleep until symptoms resolve.
The red flags that demand immediate action are the HACE and HAPE signs: confusion, an unsteady drunken gait, breathlessness while resting, a persistent wet cough, blue lips or extreme lethargy. A simple field test for HACE is the heel-to-toe walk; if a trekker cannot walk a straight line, assume cerebral oedema and descend at once. Never leave someone with worsening symptoms alone, and never let them continue up.
Diamox (acetazolamide) — what Indian trekkers should know
Acetazolamide, sold as Diamox, is the standard preventive drug. It is not a magic shield; it speeds your natural acclimatisation by making you breathe a little more, raising blood oxygen. It is most useful when you must ascend faster than ideal (for example flying into Leh) or if you have had AMS before.
A commonly cited preventive dose in wilderness medicine guidance is 125mg twice daily, started the day before you begin ascending and continued for the first two to three days at high altitude. Some itineraries with very rapid ascent use higher doses. Do not self-prescribe a regimen from a blog: see a doctor, because dosing, suitability and interactions depend on you. Diamox is a sulfa-derived drug, so people with sulfa allergy should avoid it.
Expect side effects: tingling in the fingers and toes, increased urination, and fizzy drinks tasting flat are normal and harmless. Crucially, Diamox does not treat severe AMS, HACE or HAPE; if those develop, the response is descent and emergency care, not more tablets.
Why fitness does not protect you
One of the most dangerous myths among Indian trekkers is that being fit makes you immune. It does not. AMS susceptibility is largely individual and partly genetic; very fit marathoners and soldiers get it, while unfit older trekkers sometimes sail through. Fitness helps you cover ground and enjoy the trek, but it does nothing to change how fast your body adapts to low oxygen.
Worse, fit and competitive people are often the ones who ascend too fast, push through early symptoms and ignore rest days, precisely the behaviours that cause severe AMS. Treat your previous high-altitude history, not your gym performance, as the real predictor: if you got AMS before, you are more likely to again, so plan slower and discuss Diamox with a doctor.
Practical preparation before the trek
Build sensible margins into the itinerary itself. Choose routes with proper acclimatisation days rather than the fastest schedule, and be wary of tight commercial packages that rush the ascent to fit a holiday window. If you are flying into a high-altitude airport like Leh, block rest days at the start.
Carry a small altitude kit: a pulse oximeter (a sub-90% reading at rest with symptoms is a warning sign), ibuprofen or paracetamol for headache, your prescribed Diamox if advised, and ORS for hydration. Buy travel insurance that explicitly covers high-altitude trekking and, for serious peaks, helicopter evacuation, because many standard policies exclude trekking above a certain altitude. Confirm the altitude limit in the policy wording.
Emergency protocols and when to descend
The golden rule of altitude medicine: when in doubt, go down. Descent is the only definitive treatment for serious altitude illness, and even 500 to 1,000m of descent often produces dramatic improvement. Do not wait for daylight or a scheduled stop if someone has HACE or HAPE signs; descend immediately.
- Mild AMS: stop ascending, rest, hydrate, treat the headache. Only continue up once symptoms clear.
- Symptoms not improving or worsening: descend.
- Any HACE or HAPE sign (confusion, ataxia, breathlessness at rest): descend right away and seek medical help; supplemental oxygen and emergency medication can buy time but do not replace descent.
On organised treks, tell your guide the moment you feel unwell, and never let group pressure or summit ambition override these rules. Mountains are permanent; a turned-around trek is not a failure.
Frequently asked questions
At what altitude does altitude sickness usually start?
Acute mountain sickness typically begins above 2,500 to 3,000m, though sensitivity varies by individual. Many popular Indian and overseas treks, including Leh-Ladakh, Everest Base Camp and Kilimanjaro, sit well within this zone, so acclimatisation planning matters even for routes that feel modest in distance.
How do I prevent altitude sickness without medication?
Ascend slowly. Above 3,000m, limit your sleeping-altitude gain to about 300 to 500m per night, add a rest day every 600 to 1,000m, and follow climb-high-sleep-low. Stay hydrated, avoid alcohol and sleeping pills, and do not fly straight to high altitude and immediately push higher.
What is the standard Diamox dose for altitude sickness?
Wilderness medicine guidance commonly cites 125mg of acetazolamide twice daily, started the day before ascent and continued for two to three days at altitude. Doses vary with the itinerary, so consult a doctor rather than self-prescribing. Avoid it if you have a sulfa allergy.
Does being physically fit prevent altitude sickness?
No. Fitness does not protect against AMS, which depends on how fast your body adapts to low oxygen, largely an individual trait. Fit people often ascend too quickly and push through symptoms, raising their risk. Your prior altitude history is a far better predictor than fitness.
What are the danger signs that mean I must descend?
Confusion, an unsteady drunken walk, breathlessness at rest, a persistent wet cough, blue lips or extreme drowsiness signal severe altitude illness (HACE or HAPE). These are emergencies. Descend immediately, even at night, and seek medical help. Do not wait to see if they improve.
Can I fly directly to Leh and start trekking?
Flying into Leh lands you at around 3,500m without acclimatisation, a common cause of AMS. Spend the first 24 to 48 hours resting at Leh altitude before any higher excursion, hydrate well, and consider Diamox after consulting a doctor. Do not sightsee at high passes on day one.
Does drinking more water cure altitude sickness?
No. Hydration supports acclimatisation and helps you feel better, but it does not cure AMS and cannot reverse severe altitude illness. The only reliable treatment for worsening symptoms is descent. Avoid over-drinking to the point of discomfort, and never use fluids as a reason to keep ascending.
Does my travel insurance cover high-altitude trekking?
Often not by default. Many Indian travel policies exclude trekking above a stated altitude or list it as an adventure activity needing a rider. For Himalayan or Kilimanjaro treks, buy a plan that explicitly covers your altitude and includes emergency helicopter evacuation. Verify the altitude limit in the policy wording.