Altitude sickness

Acetazolamide tablets (formerly Diamox) for altitude sickness, forced acclimatisation and altitude sleep disturbance.

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Acetazolamide 250mg

Acetazolamide 250mg (Diamox)

28-112 tablets from £14.40

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Acetazolamide 250mg28 tablets£14.40
Acetazolamide 250mg56 tablets£27.80
Acetazolamide 250mg112 tablets£49.60

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Prescription fees

Dr Fox supplies medicine on prescription and charges a small prescription fee based on the order value of each prescription.

Prescriptions are issued by our doctors online and sent electronically to our pharmacy.

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up to £20£2.00
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Medical information

Written and reviewed by a team of doctors. Dr Fox is regulated by the CQC & GPhC.


Please do not order without reading and understanding this medical information.
Print information to take with you

Most trekkers and climbers do not need, and should not take acetazolamide tablets (Diamox).

  • Altitude problems are unlikely below 2,500 metres (8,000 feet).
  • Anybody can suffer from illness caused by altitude. Nobody is immune to it.
  • The best way to reduce the risk is to acclimatise and be prepared to descend.


Ascend slowly with overnight stops at regular intervals.

  • People planning to ascend over 3,000 metres (10,000 feet) should spend a night at an intermediate elevation below 3,000 metres before they start to ascend.
  • Above 3,000 metres ascend only 300-500 metres (1,000-1,500 feet) a day to each next new sleep height.
  • If more than 500 metres (1,500 feet) of ascent is required in the day, descend back to 500 metres to sleep (climb high, sleep low).
  • For every 1,000 metres (3,000 feet) of ascent stop for 2 nights sleep before going higher.

Symptoms of mild early acute mountain sickness

Stop ascending until feeling better.

  • Headache not relieved by paracetamol and drinking a litre of water (early symptom of acute mountain sickness)
  • Fatigue and weakness.
  • Dizziness and light-headedness.
  • Difficulty sleeping.

Do not ascend if these symptoms develop. Stop until the symptoms resolve (usually 24-48hrs) or descend. Descending will usually make the symptoms go more quickly.

Ascent can be continued when these symptoms subside, usually after 24-48 hrs.

  • Do not keep ascending.
  • It helps to drink plenty.
  • Avoid alcohol and sedatives.

Emergencies requiring immediate descent

Two sets of symptoms requiring immediate descent:

  1. Fluid on the lungs
    Showing up as struggling to breath, extreme fatigue, rattling breathing, coughing, blue or grey lips and fingernails, drowsiness, collapse, confusion and death. This condition is known as HAPE (High Altitude Pulmonary Oedema). The cardinal feature is extreme shortness of breath – being short of breath when everybody else has got their breath back.
  2. Fluid on the brain
    Showing up as changes in behaviour, lethargy, and loss of coordination (unable to walk in a straight line). This can progress to coma and death. This condition is known as HACE (High Altitude Cerebral Oedema). The cardinal feature is cognitive impairment (inability to think straight and carry out normal tasks).

These two conditions are emergencies requiring immediate descent, even if this is in the night. The descent needs to be at least 500-1,000 metres (1,500-3,000 feet) and as soon as is possible. Delay can be fatal.

In addition to descent, treatment includes oxygen, steroids and hyperbarric oxygen (oxygen delivered in a high pressure chamber).

Notes about HACE and HAPE

  • Can come without any warning.
  • Can develop rapidly over a period of hours.
  • Often start at night, although can come on in the day.
  • There may be no preceding symptoms or warning.
  • Can affect people who have ascended previously to the same height without problems.
  • Can affect people who have followed the guidelines for acclimatisation.
  • Can affect people who are taking acetazolamide.
  • Can affect fit and unfit people and indigenous people including porters.

About acetazolamide (Diamox)

Acetazolamide increases the amount of urine produced and changes the acidity of the blood. The net effect is to improve breathing and reduce fluid around the brain and in the lungs. It is important to drink plenty whilst taking acetazolamide, at least 2 to 3 litres a day.

Acetazolamide is not licensed to prevent and treat altitude sickness, although it has long been used for this purpose.

Acetazolamide side effects

Most people taking acetazolamide for short courses experience no side effects.

Side effects reported include: a 'tingling' feeling in the fingers and toes, some loss of appetite, taste disturbance, flushing, thirst, headache, dizziness, fatigue, irritability, and depression.

Uses of acetazolamide

  1. In the mild acute mountain sickness (headache, fatigue, light headedness, difficulty with sleep) symptoms resolve more quickly with acetazolamide. The symptoms usually go by themselves in around 24-48 hrs. This usually reduces to around 12-24 hrs with acetazolamide.
  2. Taking acetazolamide will reduce the likelihood of altitude sickness in people who are forced to ascend without proper acclimatisation. Serious illness and even death are still possible. acetazolamide is not a substitute for acclimatisation.
  3. Acetazolamide improves the pattern of breathing during sleep at altitude and thus quality of sleep. During sleep at altitude the breathing pattern alters; rapid breaths are followed by prolonged pauses. This is not dangerous but tends to lead to poor sleep.

We do not recommend taking acetazolamide for people planning to undertake routine ascents. Most people who acclimatise properly do not need it. Taking acetazolamide can give a false sense of security.

Acetazolamide dosage

  1. For the treatment of mild early acute mountain sickness (headache, fatigue, light headedness, difficulty with sleep): Acetazolamide 250mg (one tablet) twice daily until symptoms resolve, when planned ascent can be resumed.
  2. Where rapid ascent without proper acclimatisation cannot be avoided: Acetazolamide 125mg (half a tablet) twice daily, started the day before ascent or as soon as possible after starting to ascend and continue for 2-3 days after final altitude is reached.
  3. For disturbed breathing pattern during sleep: Acetazolamide 125mg (half a tablet) twice daily. Continue until descent to an altitude where sleep is no longer a problem. Acetazolamide is not a sedative.


Stopping acetazolamide does not cause a rebound in symptoms. The symptoms will not be worse than they would have been if acetazolamide had not been taken in the first place.

Taking acetazolamide for early symptoms does not mean it is OK to keep ascending. Do not ascend until symptoms resolve completely, usually 24-48 hrs.

Acetazolamide does not mask serious underlying symptoms. It treats the cause, not the symptoms. If a person feels better on acetazolamide it is because their condition has improved.

Take a trial dose of half a tablet 3-4 days before travel to check for possible adverse reactions.

Treat altitude with respect. Do not imagine that a strong person can simply battle through. People who climb and hike in high places have a reputation for pushing themselves. When it comes to altitude; planning ahead, taking one's time and responding to one's own body are virtues.

Further information

If you wish to discuss with our site doctors please contact via or telephone +44 (0)117 2050198.

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Dr Fox supplies acetazolamide tablets on prescription - you are required to answer a short medical questionnaire before your order can be completed.

Dr Tony Steele

Authored 17 March 2010 by Dr Tony Steele
Last updated 17 January 2022

Reviewed by Dr B. Babor, Dr A. Wood, Dr P. Hunt
Last reviewed 18 February 2019


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Answer medical questions to order(altitude sickness)

Have you read the altitude sickness medical information?

 Please read altitude sickness medical information IN FULL.
Medical information in printable format (pdf).

Do you agree to Diamox (acetazolamide) being supplied to you 'off label'?

If a medicine is used for an off label (unlicensed) purpose the manufacturer is not liable in case of adverse events. Doctors take the responsibility for the prescribing.

Are you allergic to Diamox (acetazolamide) or sulpha containing medication?

If you are not sure please check with your regular doctor before ordering Diamox (acetazolamide).

Are taking any of the following medications?

  • Phenytoin or carbamezepine (anti-epileptic drugs)
  • Anti-coagulants (blood thinning drugs such as warfarin)
  • Medication to lower blood sugar (diabetic tablets)
  • Diuretics (tablets taken to remove fluid from the body)
  • Regular aspirin (more than occasional 1 or 2 aspirin every few days)

Do you plan to take acetazolamide whilst pregnant?

Have you been diagnosed with kidney or liver disease?

For organised groups; have you been advised to obtain Diamox (acetazolamide) by your group organisers?

For non-organised groups please answer 'Yes'.

Are you aware taking Diamox (acetazolamide) does NOT replace acclimatisation?

Above 3,000 metres (10,000 feet) ascend no more than 300-500 metres (1,000-1,500 feet) per day. For every 1,000 metres (3,000 feet) of ascent stop 2 nights before ascending further.

Are you aware Diamox (acetazolamide) is not advised where normal acclimatisation recommendations are followed?

Proper acclimatisation is the way to deal with altitude.

Are you aware people taking Diamox (acetazolamide) can still get mountain sickness including the very serious HAPE and HACE?

See the medical information for details.

Are you aware the sleep disturbance of altitude is treated with 125mg (half a tablet) Diamox (acetazolamide) twice daily?

Are you aware for early mild acute mountain sickness (headache, fatigue, dizziness, loss of appetite) the Diamox (acetazolamide) dose is 250mg (one tablet) twice daily?

Taking Diamox (acetazolamide) will help with these symptoms. The important thing is not to ascend until the symptoms resolve.

Are you aware in situations where rapid forced ascent cannot be avoided the dose of Diamox (acetazolamide) is 125mg (half a tablet) twice daily?

Ascent of more than 500 metres (1,500 feet) a day above 3,000 metres (10,000 feet) is dangerous with or without Diamox (acetazolamide).

Are you aware confusion, loss of co-ordination and extreme shortness of breath are serious symptoms requiring immediate descent and also possible, steroids, oxygen, hyperbarric oxygen and acetazolamide?

Do you have any further medical information or questions?

Is there anything you do not understand or do you need further help?

Do the following apply to you?

  • The medication is for my own use and I will not share with anyone else
  • I will read the patient information leaflet supplied with the medication
  • I am over 18 and I agree to identity verification checks
  • I have completed this questionnaire myself and fully understand all the information
  • My responses are honest and accurate, and I understand that this is necessary for a safe medical assessment
  • I agree to the terms & conditions, privacy policy, & data sharing policy

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