Altitude Sickness from Indian Metros — Diamox, Acclimatisation and Hospital List for 2026
By Reyansh Mehta (Reyansh Mehta covers hill stations across the Indian Himalayas — Manali, Kashmir, Ladakh, Sikkim, Spiti — with a focus on flights, road conditions, altitude acclimatisation and permit rules. He's spent 90+ days above 3,500m in the last five years.) · Published · Last updated · 12 min read
Most Indian metro residents flying to Leh, Spiti or Gurudongmar are sea-level dwellers jumping to 3,500m or higher in 90 minutes. Here is the practical 2026 guide to altitude sickness, Diamox, acclimatisation and the hospital network across the Indian Himalayas.
Why metro Indians are uniquely vulnerable to altitude
Mumbai sits at 14m above sea level. Chennai at 6m. Kolkata at 9m. Bengaluru at 920m. Delhi at 216m. Indian metros are overwhelmingly low-altitude cities — even Bengaluru, the highest of them, sits below 1,000m. When metro residents fly into Leh (3,524m), drive to Kaza (3,800m), or attempt Gurudongmar Lake (5,210m), they are jumping more than 3,000m in altitude over hours rather than days. This is one of the largest altitude transitions any tourist demographic in the world routinely makes.
The human body's haemoglobin oxygen-carrying capacity is optimised for the partial pressure of oxygen at sea level. At 3,500m, the barometric pressure is roughly 65 percent of sea level, which means each breath delivers roughly 35 percent less oxygen than your body is accustomed to. Your physiology responds with several adaptations — increased respiratory rate, increased heart rate, eventual erythropoietin release to produce more red blood cells. These adaptations take days to fully develop. In the meantime, your body operates with oxygen debt.
The clinical manifestation is Acute Mountain Sickness (AMS), a syndrome of headache, nausea, fatigue, sleep disturbance and loss of appetite. Mild AMS affects 30 to 60 percent of fly-in arrivals at 3,500m. Moderate AMS affects 15 to 25 percent. Severe AMS — including High Altitude Pulmonary Oedema (HAPE) and High Altitude Cerebral Oedema (HACE) — affects 1 to 3 percent and is potentially fatal. This guide structures the practical knowledge every Indian metro traveller should have before going to altitude.
Recognising AMS — symptoms, timing, severity scoring
AMS symptoms typically appear 6 to 24 hours after ascent to altitude. The classic constellation includes headache (the most consistent symptom), nausea or vomiting, dizziness, fatigue out of proportion to exertion, loss of appetite, and sleep disturbance (often described as breathlessness while trying to sleep, or sudden wakings with rapid breathing). The Lake Louise Score, a clinical scoring system used internationally, rates these symptoms 0-3 for severity to classify mild, moderate or severe AMS.
Mild AMS (score 3-5) is the most common presentation and typically resolves with rest, hydration, no further ascent and 24-48 hours of acclimatisation. Moderate AMS (score 6-9) requires more aggressive intervention — rest, supplemental oxygen if available, analgesics for headache, anti-emetics for nausea, and consideration of descent if no improvement in 12-24 hours. Severe AMS (score 10+) or any signs of HAPE/HACE require immediate descent to lower altitude, ideally below 2,500m.
HAPE warning signs include progressive shortness of breath even at rest, persistent dry cough that develops into wet productive cough (pink frothy sputum is a late and ominous sign), chest tightness and gurgling breath sounds. HACE warning signs include severe headache unresponsive to medication, vomiting, ataxia (inability to walk in a straight line, perform finger-to-nose test), confusion and altered behaviour. Both are evacuation emergencies, not wait-and-see conditions. The mortality rate for untreated HAPE is around 50 percent within 12-24 hours.
Diamox protocol — dose, timing, side effects
Acetazolamide (brand name Diamox in India) is the standard pharmacological prophylaxis for altitude exposure. It is a carbonic anhydrase inhibitor that increases respiratory drive, encourages bicarbonate excretion, and effectively pre-acclimatises the body to altitude. Multiple international studies have shown 50 to 70 percent reduction in AMS incidence with Diamox prophylaxis compared to placebo.
The standard adult prophylactic dose is 125mg orally twice daily, starting 24 hours before ascent to altitude and continuing for the first 48 to 72 hours at altitude. For higher altitudes (above 4,500m) or for travellers with prior AMS history, the dose can be increased to 250mg twice daily under physician guidance. The medicine is widely available across Indian pharmacies, costs roughly 50 to 80 rupees for a strip of 10 tablets, but requires a prescription. Speak to your GP before your trip — ideally 2 weeks in advance for any prescription needs.
Common side effects include tingling in fingertips and around the mouth (called paresthesia, harmless), increased urination (the drug is a mild diuretic, drink more water to compensate), and a metallic or off taste with carbonated drinks. Contraindications include sulpha drug allergy, kidney impairment, severe liver disease, pregnancy, and certain cardiac conditions. The drug is not safe during pregnancy. For travellers with diabetes, gout or significant medical history, an in-depth consultation with your GP is essential before starting Diamox.
Acclimatisation protocols — fly-in vs drive-in approaches
Acclimatisation strategy depends heavily on whether you reach altitude by air or by road. Fly-in arrivals (Delhi-Leh, Delhi-Bagdogra-Gangtok) jump 3,000m+ in 90-120 minutes with zero gradual exposure. Drive-in arrivals (Manali-Leh by road, Shimla-Spiti by road, Delhi-Manali by road) climb gradually over 1-3 days, giving the body time to adapt naturally. The two approaches require different acclimatisation protocols.
For fly-in arrivals at Leh (3,524m), the mandatory protocol is 24-36 hours of complete rest at the arrival altitude before any further ascent. No sightseeing on day 1. No higher altitude attempts on day 1. Stay in Leh town. Walk slowly only as much as needed for meals. Drink 4-6 litres of water per day. Avoid alcohol completely. Eat carbohydrate-rich meals. Sleep with head slightly elevated. Hotels with experience hosting fly-in tourists typically design the first night around rest with rooms warm enough to support breathing comfort.
For drive-in arrivals via the Manali-Leh route (gradual climb over 2 days with overnight stays at Sarchu or Pang at 4,200m+), the body has already started natural acclimatisation by the time you reach Leh. Less mandatory rest is needed but still avoid strenuous activity on the first full day. For Shimla-Kaza drive-in to Spiti, the multi-day ascent profile means acclimatisation is largely complete by arrival at Kaza (3,800m). Same principle applies — drink water, avoid alcohol, eat well, monitor for symptoms. For detailed Leh planning, see our flying to Leh guide.
The 1,000m rule and other ascent guidelines
Once above 2,500m, the international mountaineering and high-altitude medicine community uses the 1,000m rule — do not increase your sleeping altitude by more than 1,000m per day above 2,500m. This rule is designed for trekkers gaining altitude on foot but applies equally well to road journeys with overnight stays. For travellers going from Manali (2,050m) to Kunzum Pass (4,590m) in a single day, the rule is violated — which is why AMS incidence is so high on the Manali-Kaza direct route.
Climb high, sleep low is the related principle — daytime exposure to higher altitude is acceptable provided you descend for the night to a lower sleeping altitude. This is why an acclimatised traveller can do day trips to Khardung La (5,359m) from Leh (3,524m) safely — daytime exposure with overnight return to a known acclimatised altitude is much safer than spending the night at 5,000m+.
Rest days are an essential part of altitude itineraries. Build in at least one full rest day every 3-4 days of active high-altitude travel. Rest days allow physiological consolidation of acclimatisation, recovery from cumulative fatigue, and identification of any subtle AMS symptoms that might be missed during active travel days. A typical 7-day Ladakh itinerary should include the Leh arrival rest day, one rest day after Pangong or Nubra, and a winding-down day before departure.
Hospital and medical infrastructure across the Indian Himalayas
The medical infrastructure for altitude emergencies varies significantly across destinations. Leh has the strongest infrastructure with two major hospitals. The Sonam Norboo Memorial Hospital (SNM Hospital) in Leh town has a dedicated high-altitude medicine unit, oxygen supply, hyperbaric chamber (Gamow bag), and coordination capability for helicopter evacuation to Chandigarh or Delhi for severe cases. The Indian Army Hospital at Leh, while primarily for military personnel, accepts civilian altitude emergencies and has strong altitude medicine expertise.
For Manali, the District Hospital at Mission Compound provides basic emergency care including oxygen. For more serious cases, the Indus Hospital at Manali and Apollo Hospital at Naggar offer additional capacity. Critical altitude cases from Lahaul-Spiti are typically evacuated to Manali for stabilisation and then to Chandigarh PGI for definitive care. The Atal Tunnel has made this evacuation chain materially faster — the previous Rohtang Pass winter closure could leave Lahaul-Spiti cases without evacuation access for hours.
For Sikkim, the major facilities are STNM Hospital (state government hospital at Gangtok) and the Central Referral Hospital at Tadong, Gangtok. For Kashmir, Srinagar has multiple major hospitals including SKIMS (Sher-i-Kashmir Institute of Medical Sciences) and SMHS Hospital. Northeast India has more limited high-altitude medical infrastructure with Guwahati Medical College Hospital as the regional referral centre for serious cases from Arunachal, Sikkim and other Northeast destinations.
What to pack and what to carry — the high-altitude kit
Beyond your standard travel kit, high-altitude trips require specific additions. The essentials include Diamox (prescription required, 125mg twice daily for the trip duration), Paracetamol or low-dose ibuprofen for altitude headaches, ORS sachets (3-5 per person for the trip), basic anti-emetic like Ondansetron for nausea (prescription), and a personal pulse oximeter (the small finger-clip devices cost 800-2,500 rupees and let you monitor oxygen saturation).
For warmth, multiple layers work better than a single heavy garment — thermal innerwear, fleece, down jacket, windproof outer shell. Even in May the early morning at Leh airport can be below freezing. UV protection at altitude is severe because the thin air filters less ultraviolet radiation. Dark sunglasses (UV400 rated), high-SPF sunscreen (50+) and lip balm with SPF are essential. A wide-brimmed hat or cap with neck flap protects against direct sun.
Other practical items include a thermos for hot water (drinking warm water at altitude is much more comfortable than cold), small thermometer for monitoring fever or hypothermia, basic first aid supplies, and emergency contact list with hospital phone numbers. A satellite communicator (Garmin inReach or similar) is worth considering for very remote trips where mobile coverage fails. For online booking your trip insurance to cover medical evacuation, see our Inner Line Permits guide which has related preparation links.
Pre-existing conditions — who should not go to high altitude
Certain medical conditions are contraindications or relative contraindications to high-altitude travel. Absolute contraindications include severe pulmonary hypertension, recent cardiac event (myocardial infarction within 6 months), unstable angina, severe COPD or asthma requiring oral steroids, sickle cell disease, severe anaemia, and recent stroke. People with these conditions should not go above 2,500m without specialist consultation.
Relative contraindications requiring medical consultation before high-altitude travel include well-controlled hypertension (generally safe but cardiology assessment recommended), diabetes (mostly safe but Diamox-insulin interaction needs management), pregnancy (generally avoid above 3,000m, absolutely avoid above 3,500m especially in first trimester), coronary artery disease in stable phase, and any cardiac arrhythmia. Children under 2 years should not be taken above 2,500m. Children 2-12 years require careful supervision and slower ascent.
For older travellers (above 60), the rule is not about age but about cardiovascular health. A 70-year-old in good cardiovascular health may tolerate altitude well, while a 50-year-old with poorly controlled hypertension may not. Get a cardiology assessment before any trip above 3,500m if you have any cardiovascular concerns. Stress ECG or echo if recommended by your cardiologist. The investment in pre-trip medical clearance is small compared to the cost and risk of an altitude emergency in a remote location.
When to descend immediately — the non-negotiable rules
The single most important high-altitude medicine principle is that descent is always the correct response to severe symptoms. If in doubt, descend. The classic teaching is descent of 500-1,000m is the most effective treatment for any altitude illness. No drug, no oxygen, no hospital can substitute for descent in HAPE or HACE.
The non-negotiable indications for immediate descent are HAPE warning signs (progressive shortness of breath at rest, pink frothy sputum, productive cough with gurgling breath sounds), HACE warning signs (severe headache not relieved by analgesics, ataxia or inability to walk straight, confusion or altered mental status, vomiting), severe AMS not responding to rest and Diamox within 12-24 hours, and any sudden deterioration in a person who was previously stable at altitude.
The practical implementation requires planning. Know the descent options for your itinerary before you start — from Leh, descent options are by air to Delhi (only morning flights, weather-dependent) or by road to Manali (long road journey but altitude-reducing). From Spiti, descent via Manali is faster than via Shimla. From Gurudongmar Lake area, immediate descent to Lachen (2,750m) and then to Gangtok if needed. Mountain helicopter evacuation services exist but are weather and time dependent. For trip preparation including evacuation logistics, see our author hub.
Practical altitude itinerary examples — what good looks like
A well-planned 8-day Ladakh itinerary for first-time fly-in travellers might look like this. Day 1: Fly Delhi to Leh, arrive 09:30, hotel rest, light walk in Leh town, no altitude gain. Day 2: Rest day in Leh, visit Leh Palace and Shanti Stupa (within town, minimal altitude gain), early sleep. Day 3: Day trip to Indus Valley monasteries (Hemis, Thiksey, Shey) — same altitude as Leh, gradual physical exertion. Day 4: Drive to Nubra Valley via Khardung La (overnight at Diskit, 3,150m, slightly lower than Leh). Day 5: Nubra exploration, return to Leh. Day 6: Rest day in Leh. Day 7: Day trip to Pangong Lake (4,350m, full-day exposure with return to Leh for sleep). Day 8: Fly back to Delhi.
A well-planned 7-day Spiti itinerary entering via Shimla might look like this. Day 1: Drive Shimla to Sangla (2,900m), gradual altitude. Day 2: Sangla exploration. Day 3: Drive Sangla to Tabo (3,280m). Day 4: Tabo to Dhankar and Kaza (3,800m). Day 5: Kaza local exploration including Kee, Kibber. Day 6: Kaza to Manali via Kunzum Pass (4,590m daytime, descent to 2,050m at Manali for sleep). Day 7: Manali to Chandigarh. The gradual climb profile means most travellers can attempt Kaza without significant AMS.
For high-altitude destinations beyond these — Gurudongmar Lake at 5,210m, Khardung La at 5,359m for extended time, or other 5,000m+ exposure — additional planning, medical clearance and acclimatisation buffers are essential. The general principle is that altitude is patient, and your body is patient — give it time and your trip will be safer and more enjoyable. For destination guides see our Manali destination page.
Frequently asked questions
Should I take Diamox before flying to Leh?
Yes, Diamox is recommended for fly-in arrivals at Leh. The standard prophylactic dose is 125mg twice daily, starting 24 hours before your flight and continuing for the first 48-72 hours at Leh. Speak to your GP for a prescription 2 weeks before your trip. Do not start Diamox for the first time on the morning of the flight without medical advice. If you have sulpha drug allergy or other contraindications, you cannot take Diamox and need alternative acclimatisation strategies including extra rest days.
How long does altitude sickness last?
Mild AMS typically resolves within 24-48 hours with rest, hydration and no further altitude gain. Moderate AMS may take 48-72 hours to fully resolve. If symptoms persist beyond 48-72 hours without improvement, or worsen despite rest, descent to lower altitude is required. HAPE and HACE are emergencies requiring immediate descent regardless of duration. Acclimatisation is a real physiological process — by day 3-5 at altitude, most acclimatised travellers feel close to normal even at 3,500m.
Can children fly to Leh safely?
Children above 5 years generally tolerate altitude well with the same acclimatisation protocols as adults. Children under 2 years should not be taken above 2,500m. Children 2-5 years require careful supervision and ideally slower ascent (consider road journey rather than direct flight). Watch for behavioural changes (irritability, sleep disturbance, decreased activity, loss of appetite) as these may be the earliest signs of AMS in children who cannot articulate their symptoms. Consult a paediatrician before any trip above 3,000m with children under 8 years.
Is alcohol safe at high altitude?
Strongly avoid alcohol for the first 48-72 hours at altitude. Alcohol depresses respiratory drive which is exactly what your body needs more of at altitude, increases dehydration which worsens AMS symptoms, and interferes with sleep quality at a time when sleep is already disrupted. After full acclimatisation (day 4+ at altitude), moderate alcohol is generally tolerated but limit to 1-2 drinks rather than typical sea-level intake. Heavy alcohol consumption at altitude is genuinely dangerous regardless of acclimatisation status.
What is the safe rate of ascent at high altitude?
Above 2,500m, do not increase your sleeping altitude by more than 1,000m per day. Daytime exposure to higher altitude is acceptable provided you descend for sleep. Build a rest day every 3-4 days of active high-altitude travel. For fly-in arrivals (which violate the 1,000m rule by definition), the first 24-36 hours of total rest at arrival altitude is the substitute acclimatisation strategy. Never attempt the highest altitude of your trip on the first day of arrival.
Are there hospitals at Leh and Manali for altitude emergencies?
Yes. Leh has the Sonam Norboo Memorial Hospital (SNM Hospital) with a dedicated high-altitude medicine unit, oxygen, hyperbaric chamber and helicopter evacuation coordination. The Indian Army Hospital at Leh also handles civilian altitude emergencies. Manali has the District Hospital and Indus Hospital with basic emergency care including oxygen, plus Apollo Hospital at Naggar for more serious cases. For severe cases requiring tertiary care, helicopter evacuation to Chandigarh PGI or AIIMS Delhi is arranged through these hospitals.
What does a pulse oximeter tell me at altitude?
A pulse oximeter measures peripheral oxygen saturation (SpO2). At sea level, normal SpO2 is 98-100 percent. At 3,500m (Leh) without altitude sickness, typical SpO2 is 88-92 percent. SpO2 below 80 percent at altitude is concerning and below 75 percent is alarming, especially if associated with symptoms. The device is useful for monitoring trends rather than absolute values — a sudden drop in SpO2 with worsening symptoms is a red flag warranting medical attention. The small finger-clip devices cost 800-2,500 rupees and are worth carrying for high-altitude trips.
Can I get altitude sickness even if I have been to high altitude before without problems?
Yes. Previous successful high-altitude exposure does not guarantee future safety. AMS risk depends on the current ascent profile, hydration status, fatigue level, recent illness, and many variables that differ between trips. Many experienced high-altitude travellers have had unexpected AMS episodes on trips where they expected to be fine. Maintain the same acclimatisation discipline regardless of prior experience — gradual ascent, hydration, no alcohol initially, Diamox if your doctor approves, and willingness to descend if symptoms develop.