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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes. Prevention planning and, when it fits your trip, a prescription before you go; assessment of mild symptoms at altitude.
- Where it starts: usually above 2,500 metres, often 6 to 10 hours after you arrive; the faster you go up, the higher the risk.
- Symptoms: a headache with nausea, dizziness, tiredness, poor appetite or poor sleep; most cases settle within 1 to 3 days.
- Prevention: climb slowly; above 3,000 metres, sleep no more than 500 metres higher each night and rest every 3 to 4 days.
- Emergency: confusion, unsteadiness or breathlessness at rest mean go down straight away and call 112.
Do not book a video appointment if someone at altitude is confused, unsteady on their feet, unusually drowsy, breathless while resting, coughing up frothy or bloody phlegm, or has blue or grey lips. These are signs of fluid on the brain or the lungs. Go down straight away if it is safe to do so, and call 112 for mountain rescue.
Can an online doctor help with altitude sickness?
Yes. Most of what protects you from altitude sickness is planning and judgement, and both work by video. Before you travel, the doctor goes through your route, how fast you will climb and where you will sleep, and decides with you whether a preventive medicine makes sense. At altitude, the doctor can assess mild symptoms and tell you whether to rest, stay where you are or go down. Confusion, unsteadiness or breathlessness at rest need descent and emergency care, not a consultation.
How an online consultation helps with altitude sickness
- Your route checked: The doctor looks at each night’s sleeping altitude, not just the summit, because that is what drives the risk, and flags the days where you climb too fast.
- Prevention that fits the trip: A slower plan, an extra rest night or a preventive medicine: the doctor matches the measures to how high and how fast you are going.
- A clear rule for symptoms: You leave knowing which symptoms mean rest, which mean stop climbing, and which mean go down at once.
- Your medicines checked: Existing conditions and the medicines you already take are reviewed, so a preventive medicine is only prescribed when it is safe for you.
What the doctor checks in an online altitude sickness consultation
The consultation follows a fixed order, and the emergency signs come first. If you are already at altitude, the doctor asks about:
- Brain and lung warning signs: confusion, clumsiness, drowsiness, breathlessness at rest, a wet cough or blue lips.
- The pattern of symptoms: when the headache began, how high you slept, and whether you feel worse or better since you stopped climbing.
- Your plan: the altitudes ahead, how quickly you can get down, and whether you are with others who can help.
- Your health: heart or lung conditions, pregnancy, past altitude sickness, and the medicines and allergies you have.
- Other causes: dehydration, a hangover, a migraine, a cold or food poisoning can look similar at first.
Before a pre-trip consultation, have your itinerary to hand with the altitude of each overnight stop, any history of altitude sickness, and a list of the medicines you take. If you own a pulse oximeter, note your readings.
What is altitude sickness?
Altitude sickness is the body’s reaction to the lower oxygen pressure at height. The air holds the same 21% of oxygen as at sea level, but at a lower pressure, so each breath carries less of it. At about 3,050 metres, the oxygen pressure of each breath is 69% of its sea-level value. The body adjusts over 3 to 5 days, and if you go up faster than it can adapt, symptoms appear. Doctors call 1,500 to 3,500 metres high altitude, 3,500 to 5,500 metres very high, and anything above 5,500 metres extreme altitude.
Doctors describe three forms, which people often call the three stages of altitude sickness:
- Acute mountain sickness: the common, mild form. A headache with nausea, tiredness or poor sleep, usually settling within 1 to 3 days if you stop climbing.
- High-altitude cerebral oedema: fluid on the brain, the end stage of untreated acute mountain sickness, with confusion, drowsiness and loss of coordination. Without treatment, coma can follow within 12 to 24 hours of the unsteadiness starting.
- High-altitude pulmonary oedema: fluid in the lungs, usually at least 2 days after going above 3,000 to 4,000 metres. It starts with breathlessness on effort and a dry cough, and can occur without any acute mountain sickness first.
Both forms of oedema are emergencies and can be fatal without treatment. They are extremely rare below 2,800 metres, and affect about 1 to 2 people in 100 at 4,000 to 5,000 metres, more often after a fast ascent.
Altitude sickness symptoms
Symptoms usually start 6 to 10 hours after you reach a new altitude, often during or after the first night, and the headache is the core sign. Doctors diagnose acute mountain sickness when someone who has recently gone up has a headache plus at least one of the other symptoms below. It often feels like a hangover. Typical symptoms are:
- a headache, often worse at night or on waking
- loss of appetite, nausea or vomiting
- tiredness out of proportion to the effort
- dizziness or light-headedness
- poor, broken sleep
Treat any new symptom after going up as altitude sickness until proven otherwise. A headache and nausea that start more than 3 days after you stopped climbing are unlikely to be acute mountain sickness, and need a doctor to look for another cause.
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| Sign | Mild altitude sickness | Fluid on the brain | Fluid in the lungs |
|---|---|---|---|
| Headache | Common, eases with rest and pain relief | Severe, not easing | May be present |
| Thinking and balance | Normal | Confusion, clumsiness, drowsiness | Usually normal at first |
| Breathing | Short of breath on effort only | Can change late | Breathless at rest, wet cough |
| Lips and skin | Normal colour | May turn blue or grey | Blue or grey lips or nails |
| What to do | Rest at the same altitude; do not go higher | Go down at once; call 112 | Go down at once; call 112 |
Doctors check balance by asking the person to walk heel to toe in a straight line: difficulty doing so is an early warning sign of fluid on the brain. Never leave a person with symptoms alone, and never let them go higher until they have fully recovered.
Sleep at altitude
Poor sleep is the most common complaint at altitude, and it does not always mean altitude sickness. Above about 2,700 metres, almost everyone develops periodic breathing at night: cycles of fast breathing, slow breathing and short pauses. It can alarm the person sharing your tent, but it is usually harmless and tends to improve as you adjust. Alcohol and opioid painkillers slow breathing, so do not use them to help you sleep at altitude.
How to prevent altitude sickness
A slow ascent is the most effective protection, and it matters more than fitness, age or any medicine. These are the rules doctors use:
- Avoid travelling from below 1,200 metres to above 3,500 metres in a single day.
- If you fly directly to a high altitude, rest for a day before going higher.
- Spend 2 to 3 nights at about 2,450 to 2,750 metres before going higher, where your route allows it.
- Above 3,000 metres, sleep no more than 500 metres higher than the night before.
- Above 3,000 metres, take a rest day at the same altitude every 3 to 4 days.
- Across the whole trip, keep the average gain in sleeping altitude below 500 metres a day.
- Avoid alcohol and hard exercise for the first 48 hours, and keep drinking enough water.
Keep your usual coffee or tea. Stopping suddenly can cause a withdrawal headache that is easy to mistake for altitude sickness. The phrase climbers use, climb high and sleep low, describes the idea: day trips higher are fine as long as you return to a lower altitude to sleep.
Training at sea level does not prepare you, but time at altitude does: 2 or more nights above about 2,750 metres in the 2 weeks before a trip lower the risk, and the closer to departure, the better. Before a trek, check that your travel insurance covers the whole itinerary and your planned maximum altitude, including helicopter evacuation.
Who gets altitude sickness?
Anyone can, and being fit does not protect you. Of people who are not used to altitude, 9% to 25% get symptoms going up to 2,000 to 3,000 metres, and 35% to 50% at 3,500 to 4,500 metres. When people fly straight to above 3,400 metres, the rate approaches 1 in 2. Susceptibility is partly genetic, and no test predicts it. The biggest risk factors are:
- having had altitude sickness before, which is the most reliable guide to how you will react
- a fast ascent, such as a flight or a cable car to a high altitude
- how high you sleep, rather than how high you climb during the day
- normally living below 900 metres, and hard exertion on arrival
- heart or lung disease, which needs a doctor’s review before you travel
Is your trip low, moderate or high risk?
Travel doctors sort trips into three risk groups, and the group decides whether a preventive medicine is worth taking:
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| Risk group | Your trip or history | Preventive medicine |
|---|---|---|
| Low | No past altitude sickness and sleeping no higher than 2,800 m; or 2 days or more to reach 2,500 to 3,000 m, then nights rising by less than 500 m, with an extra rest day every 1,000 m | Not needed: a gradual ascent is the protection |
| Moderate | Past altitude sickness at 2,500 to 2,800 m reached in a day; going above 2,800 m in one day; or nights rising by more than 500 m above 3,000 m, with extra rest days | Worth considering, alongside a gradual ascent |
| High | Past altitude sickness above 2,800 m reached in a day; past fluid on the brain or lungs; going above 3,500 m in one day; nights rising by more than 500 m above 3,000 m without rest days | Strongly advised, alongside a gradual ascent |
How high are popular high-altitude destinations?
Many of the high places Europeans travel to sit well above the 2,500 metres where altitude sickness usually starts. In Europe itself, the risk areas are the Alps and the Caucasus. Further afield, these are the heights travel doctors plan around:
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| Destination | Height | What it means |
|---|---|---|
| Bogotá, Colombia; Quito, Ecuador | 2,644 m; 2,819 m | High altitude: 9% to 25% of new arrivals at this height get symptoms |
| Cusco, Peru | 3,399 m | Flying in is a fast ascent; sleeping the first 1 to 2 nights lower than the airport helps |
| La Paz, Bolivia; Lhasa, Tibet | 3,630 m; 3,658 m | Flying straight in puts you in the high-risk group |
| Inca Trail, Peru | about 4,200 m at its highest | Very high altitude: adjust to the height before you start |
| Everest Base Camp and the Annapurna Circuit, Nepal | 5,380 m | Up to about 3 in 10 trekkers get altitude illness, even on standard schedules |
| Mount Kilimanjaro, Tanzania | 5,895 m | Climbs in under 7 days count as high risk |
Which altitude sickness treatment might the doctor recommend?
The plan depends on whether you are preparing for a trip or already unwell at altitude. This is the framework the doctors use, in line with NHS and CDC travel guidance.
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| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| A trip that sleeps below 2,500 metres | Advice on symptoms and pacing; usually no medicine | Yes | Not usually needed |
| A fast ascent, or past altitude sickness | A slower plan, and a preventive medicine if the ascent cannot be slowed | Yes | Not usually needed |
| Mild headache and nausea at a new altitude | Rest at the same altitude, pain relief, no further ascent | Yes | If symptoms worsen, or do not ease within a day |
| Symptoms worsening despite a day of rest | Go down 300 to 1,000 metres | For guidance only | Local medical care if you do not improve after descent |
| Confusion, unsteadiness, breathlessness at rest | Immediate descent, oxygen and emergency treatment | No | Call 112 now |
Planning a high trip? A doctor can check your route and prevention plan in one consultation.
See available times →Treatment options for altitude sickness
What you can do yourself
- Stop climbing at the first symptoms and rest at the same altitude until they have gone.
- Take paracetamol or ibuprofen for the headache, at the dose on the pack. Ibuprofen does not suit everyone, including people with a stomach ulcer, kidney problems or heart failure.
- Ask a pharmacist about an anti-sickness medicine if you feel sick.
- Drink enough to keep your urine pale, eat light meals, and avoid alcohol.
- Go down 300 to 1,000 metres if symptoms get worse or have not eased after a day.
Prescription treatment
A prescription is never issued without a consultation. For a fast ascent, or if you have had altitude sickness before, the doctor may prescribe acetazolamide to help prevent it. It speeds up the body’s adjustment. It is usually started the day before you go up and continued until you have spent 2 days at your highest altitude, and it can be stopped once you start to come down without symptoms. Common side effects are tingling in the fingers and toes, needing to pass urine more often, nausea, and fizzy drinks tasting flat, so some travellers try it at home for a day or two before the trip. It is not suitable in pregnancy or after a severe allergic reaction to sulfonamide medicines, so the doctor checks your allergies and other medicines first. If the doctor prescribes, use the prescription at a pharmacy near you.
Steroid medicines and treatments for fluid on the lungs are used for severe altitude illness, alongside descent and oxygen, by doctors on the spot or in hospital.
What does not help
No medicine replaces a slow ascent, and a preventive tablet is not a reason to climb faster than planned. Pain relief can ease the headache but does not treat the cause, and carrying on upwards with symptoms is what turns a mild illness into a dangerous one. Coca leaves or coca tea and ginkgo biloba are not recommended: the evidence that they prevent altitude sickness is lacking. Small handheld cans of oxygen hold no more than 5 litres and give only brief relief.
Special situations
Altitude sickness in pregnancy
If you are pregnant, talk to a doctor before the trip. Guidance advises avoiding high altitude in the first 3 months of pregnancy. Later on, sleep no higher than about 3,000 metres, and only once a scan has confirmed a healthy, low-risk pregnancy. After 20 weeks, short stays up to 2,500 metres without heavy exercise are thought to carry minimal risk. Acetazolamide is not recommended in pregnancy, so a slow ascent is the protection.
Heart and lung conditions
Lower oxygen at altitude puts extra strain on the heart and lungs. If you have heart disease, a lung condition such as COPD, or sickle cell disease, plan the trip with a doctor before you book.
Skiing and glacier trips in the Alps
Sleeping in a resort below 2,500 metres rarely causes altitude sickness, but a cable car to a glacier above 3,000 metres can give you a headache and nausea within hours. Come back down to sleep, and treat symptoms that follow you down as a reason to stop for the day. Strong sunlight on snow is a separate risk: protect your eyes against snow blindness and your skin against sunburn.
Trekking and high mountains abroad
Treks to Kilimanjaro, the Andes or the Himalaya often climb faster than the body can adjust, especially on short itineraries. Choose a route with rest days and an experienced guide, and plan a preventive medicine with a doctor before you leave. Many high routes are remote, with limited medical care, so make sure your insurance includes helicopter evacuation. Run the medicines you are packing through the medication checker before you go.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When altitude sickness is treated online, and when you need in-person care
Treated online: prevention planning before a trip, a preventive prescription when the ascent calls for it, and assessment of a mild headache, nausea or poor sleep at a new altitude.
In-person care: confusion, unsteadiness, drowsiness, breathlessness at rest, a wet cough, blue lips, and any symptoms that do not improve after descent.
When to get in-person care
Call 112 or go to an emergency department now for:
- confusion, drowsiness, clumsiness or being unable to walk in a straight line
- breathlessness while resting, or a cough with frothy or bloody phlegm
- blue or grey lips, tongue or nails
- a severe headache with vomiting that does not ease with rest
Get medical advice the same day for:
- symptoms that have not eased after a day of rest at the same altitude
- symptoms that continue after you have gone down
- a heart or lung condition that feels worse at altitude
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about your trip: share your route and the altitude of each overnight stop, any past altitude sickness, and the medicines you take.
- Leave with a plan: what to do, what to take and for how long, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
Not sure it’s altitude sickness? Tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Headaches can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about altitude sickness
How do I know if I have altitude sickness?
Suspect it if you develop a headache plus nausea, poor appetite, tiredness, dizziness or poor sleep after going up to a new altitude, usually 6 to 10 hours after arriving and often after the first night. It feels like a hangover. Treat any new symptom after a climb as altitude sickness until proven otherwise.
Is it altitude sickness or something else?
Altitude sickness is a headache with nausea, tiredness or poor sleep that begins 6 to 24 hours after arriving above 2,500 metres and eases with rest or descent. Dehydration, a hangover, exhaustion, migraine, carbon monoxide from a tent stove and a viral infection cause similar symptoms; the giveaways for altitude are the timing after a climb and improvement on going down. Breathlessness at rest with a wet cough, or confusion and clumsiness, are the severe forms: descend and call for help.
What is the best thing to do for altitude sickness?
Stop going up and rest at the same altitude. Paracetamol or ibuprofen can ease the headache. If symptoms get worse or have not eased after a day, go down 300 to 1,000 metres, after which most people improve quickly. Confusion, unsteadiness or breathlessness at rest mean go down straight away and call 112.
What helps altitude sickness once it has started?
Stop climbing and rest at the same altitude for a day or two; do not go higher until the headache, nausea and tiredness have gone. Drink enough fluid, eat even without appetite, take paracetamol or ibuprofen for the headache, avoid alcohol and sleeping tablets, and keep warm. If symptoms worsen, or someone becomes confused, unsteady or breathless at rest, descend at least 500 to 1,000 metres straight away, which is the only treatment that always works for altitude sickness.
What are the three stages of altitude sickness?
Doctors describe three forms: acute mountain sickness, the common mild form; high-altitude cerebral oedema, fluid on the brain, which is the end stage of untreated acute mountain sickness; and high-altitude pulmonary oedema, fluid in the lungs, which can develop with or without the mild form first. The last two are emergencies.
At what altitude does altitude sickness start?
Altitude sickness usually starts above about 2,500 metres, and sometimes a little lower. The altitude where you sleep matters most, and a fast ascent, such as a flight or a cable car to a high altitude, raises the risk.
What causes altitude sickness?
Altitude sickness is caused by the lower pressure of oxygen in the air at height: each breath carries less oxygen, and if you climb faster than the body can adapt, over 3 to 5 days, fluid shifts in the brain and lungs cause the symptoms. The risk depends on how high you sleep and how fast you got there, not on fitness; having had altitude sickness before is the strongest predictor, and flying straight to above 3,400 metres gives nearly half of people symptoms.
How long does altitude sickness last?
Mild altitude sickness usually settles within 1 to 3 days if you stop climbing and rest at the same altitude. If symptoms get worse or have not eased after a day, go down 300 to 1,000 metres, after which most people improve quickly.
Can you get altitude sickness skiing in the Alps?
Altitude sickness is uncommon on Alpine ski trips, because most resorts sit below 2,500 metres. A cable car to a glacier above 3,000 metres can still cause a headache and nausea within hours, so come back down to sleep and stop for the day if symptoms persist.
Can an online doctor prescribe altitude sickness tablets?
Yes, when they suit your trip. After a video consultation the doctor can prescribe acetazolamide to help prevent altitude sickness, typically for a fast ascent or if you have had it before, and you can use the prescription at a pharmacy near you.
How do altitude sickness tablets work?
Acetazolamide makes you breathe a little faster and deeper, which speeds up the body’s adjustment to lower oxygen. It is started the day before the ascent and usually continued until you have spent 2 days at your highest altitude. It helps prevent altitude sickness but does not replace a slow climb or protect you if you ignore symptoms.
Does being fit protect you from altitude sickness?
No. Fitness makes no difference to the risk, and fit people sometimes climb faster than they should. Having had altitude sickness before is the most reliable sign that you may get it again. What does help is time at altitude: 2 or more nights above about 2,750 metres in the 2 weeks before a trip.
Should I drink more water at altitude?
Drink enough to keep your urine pale, because dry mountain air and effort increase fluid loss. Drinking far more than you need does not prevent altitude sickness, and dehydration and altitude sickness can feel alike, so a headache is a reason to rest as well as drink.
Can I drink alcohol at altitude?
Avoid alcohol for the first 48 hours at a new altitude. It worsens sleep, adds to dehydration and makes early altitude sickness harder to recognise.
When is altitude sickness an emergency?
With altitude sickness, confusion, drowsiness, unsteadiness, breathlessness while resting, a cough with frothy or bloody phlegm, or blue lips are emergencies. Go down straight away if it is safe to do so, and call 112 for mountain rescue.
- Altitude sickness, NHS, National Health Service (UK), reviewed 31 July 2023.
- High-altitude travel and altitude illness, CDC Yellow Book, Centers for Disease Control and Prevention, 2025.
- Altitude illness: factsheet, TravelHealthPro, National Travel Health Network and Centre (NaTHNaC, UK), updated 9 February 2023.
- Altitude and travel, Fit for Travel, NHS National Services Scotland, accessed 15 October 2026.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
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