Altitude sickness can affect anyone who travels to high places too quickly, usually above 2,500 metres. It's common on treks to Everest Base Camp and Kilimanjaro, and on trips to high cities such as Cusco or La Paz. The best protection is a slow ascent, and for some trips a prescriber may also recommend acetazolamide tablets to help your body adjust. MedsRus can prescribe acetazolamide after a short online consultation with a UK prescriber, and send it by tracked delivery before you travel.
Altitude sickness symptoms
Symptoms usually start 6 to 24 hours after you reach altitude. Mild altitude sickness, also called acute mountain sickness, can feel like a bad hangover:
- headache;
- feeling sick, or being sick;
- dizziness and tiredness;
- loss of appetite;
- poor sleep.
Serious altitude sickness needs emergency descent. There are two rarer, life-threatening forms. Fluid on the lungs (high altitude pulmonary oedema, or HAPE) causes breathlessness at rest, a cough and sometimes pink, frothy phlegm. Fluid on the brain (high altitude cerebral oedema, or HACE) causes confusion, clumsiness, drowsiness or a severe headache that doesn't ease. If anyone in your group develops these, go down straight away and get medical help.
How to prevent altitude sickness
- Go up slowly. Above 3,000 metres, raise the altitude you sleep at by no more than 300 to 500 metres a day.
- Build in rest days. Spend an extra night at the same height every 3 to 4 days.
- Climb high, sleep low where the route allows.
- Drink enough water, avoid alcohol for the first couple of days, and take it easy when you first arrive.
- Never go higher with symptoms. If they get worse, go down.
Being fit doesn't protect you, and having been fine on one trip doesn't guarantee you'll be fine on the next.
Acetazolamide for altitude sickness
Acetazolamide helps your body adjust to lower oxygen levels more quickly. It's used to help prevent altitude sickness on trips where a slow ascent isn't possible, such as flying straight into a high city, or on routes that climb quickly, like most routes up Kilimanjaro.
It isn't a substitute for a sensible ascent, and it won't stop serious altitude sickness if you keep climbing with symptoms.
Off-label use
Acetazolamide is licensed in the UK for other conditions, such as glaucoma, but not for altitude sickness. Prescribing it to prevent altitude sickness is well established and in line with UK travel health guidance, but it counts as "off-label" use. Our prescriber will explain what this means during your consultation before deciding whether it's right for you.
How to take it
Your prescriber will confirm the dose for your trip. It's usually started 1 to 2 days before you begin your ascent and continued until you've spent 2 to 3 days at your highest altitude, or until you start coming down. If you can, try a dose at home before you travel so you know how it affects you.
Side effects
- tingling in the fingers, toes or face;
- needing to pee more often;
- fizzy drinks tasting flat;
- feeling sick, or tiredness.
These are usually mild. Stop taking it and get medical advice if you develop a rash.
Who shouldn't take acetazolamide
It isn't suitable if you're allergic to sulfonamide ("sulfa") medicines, are pregnant or breastfeeding, or have serious kidney or liver problems. Tell the prescriber about any other medicines you take, especially high-dose aspirin.
Other travel health
Heading somewhere with a malaria risk? See our malaria tablets page. For long-haul flights, our jet lag treatment page explains how to adjust to a new time zone, and our travel health checklist helps you plan before you go.
How to order altitude sickness tablets from MedsRus
- Complete a short consultation about your trip (destination, highest altitude and dates) and your health.
- A UK prescriber reviews it and, if it's suitable, approves acetazolamide with dosing instructions for your itinerary.
- We send it by tracked delivery. Order at least a week before you travel.
Altitude sickness FAQs
At what altitude do you get altitude sickness?
It's most common above 2,500 metres, though some people notice symptoms lower down, especially after a fast ascent.
Do I need altitude sickness tablets for Kilimanjaro?
Many trekkers take acetazolamide for Kilimanjaro because most routes climb quickly. Our prescriber will advise based on your route and how many days it takes.
Can I take acetazolamide to treat symptoms once they start?
It's mainly used to prevent altitude sickness. If you get symptoms, stop climbing and rest, and go down if they don't improve. Don't rely on tablets to keep going.
Does acetazolamide stop all altitude sickness?
No. It lowers the risk, but a slow ascent is still essential.
Is altitude sickness dangerous?
Mild altitude sickness usually settles with rest. HAPE and HACE are life-threatening and need immediate descent and medical help.
Can children get altitude sickness?
Yes, and they may not be able to describe their symptoms. Our service is for adults, so ask a travel clinic about children.
Further reading
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