Altitude sickness tablets & advice for mountaineers and expeditions
Trekking Kilimanjaro or Everest Base Camp, walking the Inca Trail, or heading out on a high-altitude expedition? Altitude sickness can affect anyone above about 2,500 m — regardless of fitness. We provide pre-expedition consultations with acclimatisation advice, an emergency plan, and altitude sickness tablets (acetazolamide / Diamox) where appropriate — plus any travel vaccines for the same trip.
Medically reviewed by Muhammad Adnan, Superintendent Pharmacist (GPhC 2073652) · based on NaTHNaC (TravelHealthPro) and NHS guidance · last reviewed June 2026.
What is altitude sickness?
At altitude there is less oxygen in the air, and your body needs time to adjust — a process called acclimatisation. Altitude sickness (acute mountain sickness, or AMS) happens when you ascend faster than your body can adapt. It can start at around 2,500 m and becomes more likely the higher and faster you go. It is not a sign of being unfit — strong, experienced climbers get it too — and you cannot reliably predict it from previous trips. Most cases are mild and settle with rest, but altitude sickness can progress to two dangerous conditions if ignored.
Know the three forms — and the danger signs
AMS — mild
Like a hangover: headache plus nausea, tiredness, dizziness, poor appetite or disturbed sleep. Stop ascending, rest and hydrate until it settles.
HACE — emergency
Fluid on the brain: an unsteady, drunken-looking walk, confusion, or drowsiness. Descend at once and get urgent help; dexamethasone may be used.
HAPE — emergency
Fluid in the lungs: breathlessness at rest, a cough, tightness and exhaustion. Descend at once, get oxygen and urgent help; nifedipine may be used.
The golden rule: never go higher with any symptoms of altitude sickness, and if symptoms are severe or getting worse, descend. Descent is the single most effective treatment — medication and oxygen buy time, but coming down is what saves lives.
The acclimatisation rules that prevent it
Gradual ascent is the foundation of staying well at altitude. The widely used rules of thumb are:
- Above 3,000 m, try not to increase your sleeping altitude by more than 300–500 m per day.
- Take a rest day every 3–4 days, or roughly every 1,000 m gained.
- “Climb high, sleep low” — it is fine to walk higher during the day, but sleep at a lower altitude.
- Stay well hydrated, eat enough, and avoid alcohol and sedatives, especially in the first days.
- Build a flexible itinerary with spare days, so you can rest or descend without losing the whole trip.
- Know the symptoms, watch your group, and agree a plan for what you'll do if someone is affected.
Altitude sickness tablets: acetazolamide (Diamox)
Acetazolamide, better known by the brand name Diamox, is the main tablet used to prevent and ease altitude sickness. It gently stimulates your breathing, which helps your body acclimatise faster to the thinner air. Taken for prevention it reduces the likelihood of AMS; it can also help treat mild symptoms.
How it's usually taken
- A common preventive dose is 125 mg twice a day.
- Started about 24 hours (1–2 days) before you begin ascending.
- Continued for 2–3 days after reaching your highest sleeping altitude (or while still climbing).
- The exact dose and plan are decided at your consultation.
Good to know
- Common, harmless effects: tingling in fingers/toes, passing urine more often, and fizzy drinks tasting odd.
- It contains a sulfonamide — tell us about any sulfa allergy.
- It's an aid to acclimatisation, not a reason to ascend faster.
- For severe illness, dexamethasone (HACE) and nifedipine (HAPE) may be carried on expeditions — alongside descent and oxygen.
Acetazolamide is a prescription-only medicine. We assess your itinerary, ascent profile and medical history before prescribing, and explain exactly how and when to take it.
Treks and expeditions where it matters
If your trip takes you above ~2,500 m, altitude advice is worth having. Common examples:
- Africa: Kilimanjaro (5,895 m), Mount Kenya, the Atlas Mountains / Toubkal.
- Asia: Everest Base Camp, Annapurna and the Nepal trails, Ladakh and Leh, Tibet.
- South America: the Inca Trail and Machu Picchu, Cusco, the Andes, Aconcagua, Bolivia's La Paz and Lake Titicaca.
- Expeditions & skiing: high-altitude climbing trips, ski-mountaineering and high resorts.
Altitude FAQ
Altitude sickness — your questions answered
Important: This page is general information based on NaTHNaC (TravelHealthPro) and NHS guidance and is not a substitute for individual medical advice. Altitude medication is prescribed only after an assessment. Descent and urgent medical help are the priority for severe altitude illness (HACE/HAPE). Sources: TravelHealthPro altitude illness factsheet · NHS altitude sickness.
Planning a trek or expedition?
Book a pre-expedition consultation at our Timperley clinic, near Manchester. We'll review your route, give acclimatisation and emergency-plan advice, prescribe altitude sickness tablets where appropriate, and sort any travel vaccines for the same trip — for travellers across Manchester, Trafford, Stockport and Cheshire.