Product Description

Acetazolamide also known as Diamox is a carbonic anhydrase inhibitor licenced for the treatment of glaucoma,  fluid retention and epilepsy.  Like many online doctor services and high altitude medicine specialists, we prescribe this medicine off-label for the prevention of altitude sickness in travellers ascending to altitudes over 2500m.  Patient information leaflets issued with this medicine will not provide advice about the use of this medicine for Altitude sickness.

This medicine is usually effective for speeding up the acclimatisation process, but importantly it is still possible to develop symptoms of acute mountain sickness (AMS), pulmonary oedema (HAPE) or cerebral oedema (HACE) whilst taking this medicine.  Slow ascents are the key to safe travel to high altitude destinations, but Acetazolamide can help.

Acetazolamide works to counter the effect of lower oxygen pressure in high altitude regions.  As you ascend oxygen pressure drops, which means you absorb less oxygen with each intake of air to your lungs.  Acetazolamide removes Bicarbonate from your body, increasing the acidity of your blood (known as metabolic acidosis).  This change to blood pH triggers a slightly increased respiratory rate, which in turn increases the amount of oxygen you intake over time.

Other medicines can be used for the prevention of AMS, HAPE or HACE but Acetazolamide was shown in trials to be the one of the most effective.  If Acetazolamide is unsuitable for you our specialist may be able to offer you an alternative.



Acetazolamide for the prevention of altitude sickness should be dosed as follows:

Half a tablet (125mg) twice daily.  This should be started two days before ascent over 2500m and then continued twice daily until you have reached your highest altitude or you are suitably acclimatised.  

We would also recommend you try Acetazolamide at home before your trip to ensure you tolerate the medicine ok.  It is never a good idea to try new things in high altitude remote locations where medical facilities may not be easy to access.


This medicine is being used "off-label". This means that it is not being used for its licenced indication. It is however the most commonly prescribed medicine for preventing acute mountain sickness in travellers visiting high altitudes.




This medicine contains the following ingredients:

Active Ingredients: Acetazolamide 250mg

Inactive Ingredients: Dicalcium phosphate, Corn starch, Magnesium stearate, Sodium starch glycolate, Povidone


This list is not exhaustive so please refer to the product leaflet for further information and advise our team of any allergies or intolerances before purchase.

Side Effects

Like all medicines, Acetazolamide can cause side effects, although not everybody gets them.

All medicines can cause allergic reactions although serious allergic reactions are infrequent. Any sudden wheeziness, difficulty in breathing, swelling of the eyelids, face or lips, rash or itching (especially affecting your whole body) should be reported immediately.

Acetazolamide 250mg Tablets can affect the liver and kidneys. If you experience pain in your lower back, pain or burning when you pass urine, have difficulty passing urine, or you stop passing urine, have blood in your urine, pale stools, or if your skin or eyes look slightly yellow, you should contact your doctor.

Not known: frequency cannot be estimated from the available data

  • headache
  • diarrhoea
  • feeling or being sick, loss of appetite, thirst, or a metallic taste in the mouth
  • dizziness, loss of full control of arms or legs
  • looking flushed
  • a need to pass urine more often than normal
  • tiredness or irritability
  • feeling over-excited
  • a tingling or numbness in the fingers or toes, or coldness in the extremities.
  • depression
  • drowsiness or confusion
  • a loss of interest in sex
  • ringing in the ears or difficulty in hearing
  • temporary short-sightedness which subsides when the dosage is reduced or treatment is stopped.
  • Decrease in vision or pain in your eyes due to accumulation of fluid in the vascular layer of the eye (choroidal effusion or choroidal detachment). 

Rare cases of skin rashes including an increased sensitivity to sunlight have been reported. If you experience any unusual skin rashes, inform your doctor.

Contact a doctor immediately if you experience a serious skin reaction: a red, scaly rash with bumps under the skin and blisters (exanthematous pustulosis). The frequency of these side effects is not known (cannot be estimated from the available data).

If any of the side effects become serious or notice any side effects not listed in this leaflet, please tell your doctor or pharmacist.


Acetazolamide is not suitable for everyone.  Do not use this medicine if:

  • you are allergic to sulphonamides
  • you have severe liver problems
  • you have or have ever had severe kidney problems
  • you have a particular type of glaucoma known as chronic non-congestive angle closure glaucoma
  • you have Addison's disease, reduced function of the adrenal glands
  • you have low blood levels of sodium and/or potassium
  • high blood levels of chlorine

Speak with our specialist pharmacist before using Acetazolamide if:

  • you have or have ever had kidney problems such as kidney stones
  • you have lung problems such as chronic bronchitis or emphysema, which cause difficulty in breathing
  • if you are over the age of 65
  • a small number of people being treated with anti-epileptics such as Acetazolamide have had thoughts of harming or killing themselves, if at any time you have these thoughts, immediately contact your doctor and discontinue using acetazolamide

Acetazolamide 250mg Tablets may affect some medical tests. If you visit a hospital or clinic for any medical tests, you should tell the doctor concerned that you are taking Acetazolamide 250mg Tablets.

A decrease in vision or eye pain could be a symptom of fluid accumulation in the vascular layer of the eye (choroidal effusion or choroidal detachment). This can happen within hours of taking Acetazolamide 250mg Tablets. Talk to your doctor promptly if you experience these symptoms.


Other medicines and Acetazolamide 250mg Tablets

The effects of any of these medicines may change, particularly if you are taking, or using, any of the following:

  • Cardiac glycosides e.g. Digoxin
  • Blood pressure medicines
  • Anticoagulants e.g. Warfarin
  • Diabetes medicines to lower blood sugar e.g. Gliclazide
  • Epilepsy medicines
  • Drugs which interfere with folic acid, eg methotrexate, pyrimethamine, or trimethoprim
    steroids such as prednisolone
  • Aspirin and related medicines, eg salicylic acid or choline salicylate for mouth ulcers
  • Similar medicines like Brinzolamide or Dorzolamide
  • Amphetamines (a stimulant), Quinidine (treats an irregular heart beat), Methenamine (prevents urine infections) or Lithium (treats severe mental problems)
  • Sodium bicarbonate therapy (used to treat high states of acid in your body)
  • Ciclosporin (used to suppress the immune system).



Acetazolamide 250mg Tablets SHOULD NOT be taken if you are pregnant, think you are pregnant or are planning to become pregnant.


It may be taken when breastfeeding but only on the advice of the doctor.

Driving and using machines

If Acetazolamide 250mg Tablets make you feel drowsy or confused you should not drive or operate machines. Acetazolamide 250mg Tablets can occasionally cause short-sightedness; if this happens and you feel that you can no longer drive safely, you should stop driving and contact your doctor.

Patient Information Leaflet

Please follow the link to view the patient information leaflet

Frequently Asked Questions

Can you buy Acetazolamide over the counter in the UK?

Acetazolamide tablets are a prescription only medicine (POM), which means that they cannot be bought over the counter routinely at your local pharmacy like Boots, Asda or Superdrug.

It can however be prescribed by doctors and other non-medical healthcare professionals.


Can you buy Acetazolamide whilst abroad eg in Cusco?

Purchasing medicines in the UK before travel is much safer than purchasing medicines whilst away.  Not all medicines are licenced in all countries, and medicines available here in the UK may not be available at your destination and vice versa. 

Europe has some of the more stringent regulatory rules to ensure medicines that arrive in our countries are safe and effective.  In other parts of the world, these regulatory mechanisms may not be as strict.  This may mean counterfeit or poor-quality medicines make their way into the supply chain.

Cost- you may think that it would be cheaper to buy your medicines outside of the UK, but that isn't always the case.  We have heard many a story about the high cost of medicines outside the UK.  



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