Altitude Sickness Prevention

Yes. A pre-travel assessment can review your planned maximum altitude, rate of ascent, sleeping altitude, previous altitude illness, medical history, pregnancy status, medicines and access to emergency descent or evacuation.

No. NaTHNaC advises that preventive medication is not necessary for low-risk itineraries. Acetazolamide may be considered in addition to gradual ascent for moderate- or high-risk situations.

No. NaTHNaC identifies Acetazolamide, including Diamox, as the preferred preventive medicine but notes that its use for altitude illness prevention is unlicensed in the UK.

No. Preventive medication is not a substitute for acclimatisation. A sensible ascent profile remains the most important way to reduce altitude-illness risk.

Altitude illness occurs when the body does not acclimatise adequately to the reduced oxygen pressure at high altitude. It includes acute mountain sickness, high-altitude cerebral oedema and high-altitude pulmonary oedema.

Acute mountain sickness, or AMS, commonly causes headache together with symptoms such as nausea, dizziness, fatigue or disturbed sleep after ascent to altitude.

High-altitude cerebral oedema, or HACE, is a severe and potentially fatal form of altitude illness involving brain swelling. Features can include severe headache, confusion, marked drowsiness and loss of coordination or inability to walk normally.

High-altitude pulmonary oedema, or HAPE, is fluid accumulation in the lungs at altitude. Symptoms can include breathlessness out of proportion to exertion, breathlessness at rest, cough, weakness and worsening exercise tolerance. It is a medical emergency.

Risk rises as sleeping altitude and ascent rate increase. Individual susceptibility varies, so previous tolerance of altitude does not guarantee protection on a future trip.

Acetazolamide is a carbonic anhydrase inhibitor. At altitude it promotes acclimatisation by producing a mild metabolic acidosis that stimulates ventilation.

NaTHNaC recommends Acetazolamide 125 mg twice daily for prevention of altitude illness in suitable adults.

Start Acetazolamide one day before ascent to high altitude.

Continue it during ascent and for at least 2 days after reaching the highest altitude. If you begin descending from the high point and have no symptoms, NaTHNaC advises that preventive medication can be stopped when descent begins.

Continue the preventive regimen while you are continuing to gain sleeping altitude and until you have spent at least 2 days at the highest altitude, unless your clinician advises otherwise.

NaTHNaC recommends taking a trial dose for 1 or 2 days before travel to check how well you tolerate common adverse effects.

Commonly reported effects include increased urination, tingling or pins and needles, taste disturbance, nausea, vomiting, headache, dizziness and fatigue.

Taste disturbance is a recognised effect of carbonic anhydrase inhibition, and some people notice that carbonated drinks taste unusually flat or metallic while taking Acetazolamide.

Yes. It has a mild diuretic effect and can increase urine output, especially when treatment begins.

Current UK product information contraindicates Acetazolamide in marked kidney or liver disease, low sodium or potassium levels, adrenal failure, hyperchloraemic acidosis and hypersensitivity to Acetazolamide or sulphonamides.

Current UK Diamox product information states that it should not be used in people who are hypersensitive to sulphonamides. Any previous sulphonamide reaction must therefore be reviewed before treatment.

Marked kidney disease or dysfunction is a contraindication. A history of kidney stones also requires caution because Acetazolamide can increase the risk of further calculi.

Marked liver disease is a contraindication. Current product information specifically advises against use in hepatic cirrhosis because of the risk of hepatic encephalopathy.

Yes. Acetazolamide increases urinary loss of bicarbonate and can affect sodium and potassium balance. It is contraindicated when sodium or potassium levels are already depressed.

A previous history of renal stones is not an automatic contraindication, but current product information advises balancing the expected benefit against the risk of precipitating further stones.

Important interactions include high-dose aspirin or salicylates, lithium, ciclosporin, some antiepileptics, sodium bicarbonate, methenamine and other carbonic anhydrase inhibitors. All regular medicines should be reviewed before treatment.

Current product information warns that concurrent Acetazolamide and aspirin can cause severe acidosis and increase central nervous system toxicity, particularly with higher salicylate doses.

Concurrent sodium bicarbonate can increase the risk of kidney-stone formation and should be reviewed before use.

Yes. Acetazolamide increases lithium excretion and can reduce blood lithium levels, potentially altering treatment control.

Yes. Product information describes interactions with medicines including phenytoin, primidone and carbamazepine. People taking antiepileptic treatment require medication review before Acetazolamide is prescribed.

NaTHNaC advises avoiding travel from below 1,200 metres to above 3,500 metres in a single day where possible. Above 3,000 metres, avoid increasing sleeping altitude by more than about 500 metres per day.

Above 3,000 metres, NaTHNaC recommends a rest day at the same altitude every 3 or 4 days.

Do not ascend to sleep at a higher altitude while you have symptoms of altitude illness. Stay at the same altitude and monitor closely, or descend if symptoms worsen or are severe.

NaTHNaC advises attempting descent if altitude-illness symptoms worsen at the same altitude or if symptoms are severe. Descent is the key treatment for serious altitude illness.

No. NaTHNaC specifically advises never leaving a person with altitude illness alone.

Stop further ascent. Rest at the same altitude, monitor symptoms and avoid sleeping higher. If symptoms worsen, fail to improve or become severe, descend and seek medical help.

Acetazolamide can support acclimatisation and may have a role in treatment plans, but it must never delay descent or emergency care for severe altitude illness, HACE or HAPE.

Supplemental oxygen can be useful in serious altitude illness where available, but evacuation or descent remains critical and should not be delayed while waiting for oxygen or medication.

No. Maintain normal hydration, but excessive fluid intake does not prevent altitude illness and can be harmful. Dehydration can worsen how you feel, so drink appropriately for activity and conditions.

Confusion, inability to walk normally, severe drowsiness, breathlessness at rest, rapidly worsening breathlessness, collapse or other features of HACE or HAPE require immediate descent and emergency medical help.

Breathlessness at rest can indicate high-altitude pulmonary oedema. Stop ascent, descend urgently and obtain emergency medical assistance.

Confusion or loss of coordination at altitude can indicate high-altitude cerebral oedema. This is an emergency requiring immediate descent and medical help.

Current UK product information states that Acetazolamide should not be used in pregnancy, particularly during the first trimester. Pregnant travellers should obtain specialist advice and carefully reconsider high-altitude itineraries.

Acetazolamide is present in breast milk at low levels. Current product information advises extreme caution during breastfeeding, so individual clinical review is required.

Seek urgent medical advice for severe rash, facial swelling, breathing difficulty, sudden visual loss or eye pain, marked shortness of breath, jaundice or symptoms suggesting a serious blood, liver or lung reaction.

Yes. NaTHNaC recommends insurance that specifically covers the planned itinerary, maximum altitude and activities, including helicopter evacuation where appropriate.

NaTHNaC recommends travelling with an experienced guide who can recognise altitude illness, manage ascent appropriately and arrange descent or evacuation when necessary.

If prevention is clinically appropriate, the supply should cover the planned ascent, the time at the highest sleeping altitude and the required continuation period, with clear written instructions on ascent, side effects and emergency descent.