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Acetazolamide 250mg Tablets

*The brand supplied may vary. Please contact us if you require a specific brand.

Acetazolamide 250mg Tablets (28 tablets)

Order before 3pm for delivery from Fri. 30 Jul and Mon. 02 Aug.

Description for Acetazolamide 250mg Tablets

Acetazolamide is the generic version of the discontinued branded treatment Diamox. It is commonly prescribed ‘off-label’ to prevent or reduce the symptoms of altitude sickness, and sold in packets of 250mg tablets.

If you suffer from altitude sickness or mountain sickness, or you’re planning to spend time at altitude (above 2,500-3000 metres), get a free consultation today. Acetazolamide can keep you from suffering symptoms, such as headaches, nausea, and dizziness. 

If Acetazolamide is right for you, we’ll give you a prescription that you can use to place an order for same day dispatch (before 4pm) anywhere in the UK. 

Acetazolamide (Diamox) Information

  • Age: 18 Years +

    Maximum per order: 2

  • Pregnancy: N/A

    Breastfeeding: N/A

Acetazolamide 250mg tablets (also known as Diamox) are available to buy from The Independent Pharmacy Online Doctor service, following a free consultation, to help to prevent and treat altitude sickness. To find out more about acne and see all the available treatments, see our Altitude Sickness page.


What does Acetazolamide treat?

Acetazolamide has several applications (such as glaucoma, fluid buildup, epilepsy) but is widely prescribed 'off-label' to prevent or reduce the symptoms of altitude sickness. Acetazolamide can actively reduce nausea, dizziness, headache and shortness of breath associated with rapid ascents (usually anything above 10,000 feet or 3,048 metres).


Acetazolamide 'off-label'

The prescription is ‘off-label’ because Acetazolamide was initially licensed to treat conditions other than altitude sickness, so its original instructions will not match your condition. 'Off label' means that the medicine is being used to treat a condition other than those that it was initially licensed to treat. This means that there is less established data regarding the effectiveness of this treatment for the condition which it is prescribed and means that the instructions contained in the product information leaflet will not match the condition you are treating. 

Click here to read studies on the effectiveness of Acetazolamide in treating Altitude Sickness 'off label'. You should always follow the instructions on the dispensing label on your medicine and contact us if you have any questions.


What does Acetazolamide (Diamox) do?

Acetazolamide 250mg tablets works to treat altitude sickness by increasing the amount of urine produced, consequently altering the acidity of the blood. This leads to a reduction in fluid in the lungs and around the brain. The result is improved breathing and relief from the symptoms of altitude sickness.

How long does Acetazolamide take to work?

How long it takes for Acetazolamide to take effect depends on the person, but it’s recommended that you start taking it a day or two before you expect to need it, and continue using it during the ascent and for two or three days after you’ve reached the peak of your trip.


Effect on recovery rate

Without medication, the symptoms of altitude sickness will usually subside in around 24-48 hours if the proper procedures are followed. Taking Acetazolamide 250mg tablets has been shown to cut recovery time in half (between 12-24 hours).


No substitute for acclimatisation

Taking Acetazolamide will help to decrease the likelihood of experiencing altitude sickness in people who are forced to ascend without the proper acclimatisation. However, Acetazolamide should not be seen as a substitute for acclimatisation. Rapid ascents are dangerous with or without Acetazolamide usage.


Breathing improvement & regulation

Sleeping at altitude alters a person’s breathing patterns. It is usually characterised as short, rapid breaths followed by prolonged pauses. This is quite normal and is not considered dangerous. However, it can lead to a poor quality of sleep. Taking Acetazolamide tablets will help improve this pattern of breathing, resulting in a better quality of sleep.


Height risk of altitude sickness

Symptoms are unlikely to develop at heights below 2,500 metres (8,000 feet), so most trekkers, climbers or hikers shouldn’t need to take Acetazolamide. That said, anyone can suffer from altitude sickness - even if they are very fit, and it can occur at lesser heights in very rare cases.


How to reduce the risk of altitude sickness

You can minimise the risk of experiencing altitude sickness by following established protocols:

  • Acclimatise by ascending slowly with overnight stops at regular intervals.
  • If you are planning to climb over 3,000 metres (10,000 feet), spend a night at an intermediate elevation below 3,000 metres before starting your final ascent.
  • When over 3,000 metres, limit your rate of ascension to 300-500 metres (1,000-1,500 feet) per day, stopping to sleep each night.
  • After every 1,000 metres (3,000 feet) of ascent, rest for a couple of nights before climbing any higher.
  • If you climb more than 500 metres (1,500 feet) during one day, descend 500 metres before sleeping.


Symptoms of mild early acute mountain sickness

If you experience any of the following symptoms, stop ascending until you feel better:

  • A headache that won’t be relieved by taking Paracetamol and drinking water.
  • Fatigue and general weakness.
  • Dizziness and a feeling of being light-headed.
  • Difficulty sleeping.

These symptoms usually resolve within a period between 24 and 48 hours. Descending can help you feel better more quickly. Be sure to stay hydrated and avoid alcohol and sedatives. Once the symptoms have passed, you can resume your ascent.


Emergency situations requiring immediate descent

There are two life-threatening emergency situations in which you need to descend immediately:

Number 1: you develop fluid on the lungs. This is known as HAPE (High Altitude Pulmonary Oedema). Most notably, it causes an extreme shortness of breath, making you take much longer to recover from exertion. Be mindful of the following symptoms:

  • Shortness of breath.
  • Difficulty taking a breath.
  • A noisy, rattling sound while breathing.
  • Extreme fatigue.
  • A persistent cough.
  • Blue or grey lips and fingernails.
  • A tendency to collapse.
  • Drowsiness.
  • Confusion.

Number 2: you develop fluid in the brain. This condition is known as HACE (High Altitude Cerebral Oedema) and causes cognitive impairment: an inability to think straight. Left untreated, it can lead to a coma or even kill you. Look out for these symptoms:

  • Lethargy.
  • Behavioural shifts.
  • Loss of coordination (inability to walk in a straight line).

Both conditions can appear without warning, at any time, and in those who have previously handled higher elevations without issue. They can affect people in peak physical condition, and hit visitors and indigenous people alike. Taking Acetazolamide does not fully protect you.

If you develop HACE or HAPE, you must descend immediately, even during the night, and by at least 500-1,000 metres (1,500-3,000 feet). Any delay can be fatal. These conditions can be addressed with oxygen and steroid treatments, but there are no guarantees, and descending right away is critical.


Use during pregnancy or breastfeeding

Acetazolamide has been found safe for use while breastfeeding, and may be deemed viable for a pregnant woman following a consultation. Pregnant women, though, should not be climbing at altitude or doing anything physically dangerous, so be extremely cautious.


What to do if Acetazolamide is unavailable

If you have no Acetazolamide to ease your trip, focus on the following precautions:

  • Stay as hydrated as you can.
  • Avoid alcohol.
  • Do not smoke.
  • Avoid using sleeping pills.
  • Consume a high calorie diet.
  • Rest as much as you possibly can


Acetazolamide or Diamox?

Acetazolamide used to be known as Diamox tablets. However, the brand Diamox has been discontinued. The medication has since been re-branded as generic Acetazolamide 250mg tablets, which was the same active ingredient found in Diamox. Acetazolamide belongs to a category of medicines called diuretics. A diuretic is any substance that increases the production of urine, thus promoting the excretion of water from the body. Acetazolamide is manufactured by MercuryPharma. The tablet itself is white, round and convex with “FW 147” marked on one side. The other side of the tablet is scored into quarters. Acetazolamide is a prescription only medicine (POM). 

*Prescription medicines are supplied subject to a medical consultation at the discretion of a doctor.

Acetazolamide (Diamox) dosage

Your required dose of Acetazolamide will depend on the severity of your symptoms. You or a member of your group will need to decide on the most appropriate treatment. If you have a doctor or other healthcare professional on your trip, you should seek their advice. 

Here are some general guidelines:

  • To treat mild early acute mountain sickness (headache, fatigue, lightheadedness, difficulty sleeping), take one 250mg tablet of Acetazolamide 250mg twice daily until symptoms resolve. You can then resume climbing.
  • To prepare for rapid ascent without proper acclimatisation, take one 250mg tablet of Acetazolamide twice daily, beginning the day before ascent or as soon as possible after beginning, and keep taking the tablets for a few days after reaching final altitude.
  • o treat disturbed breathing patterns, take half of one 250mg tablet of Acetazolamide twice daily until reaching an altitude comfortable for sleeping.

Remember: even if you take Acetazolamide, it is still important to properly acclimatise. You should never ascend further until your symptoms have completely gone and you are properly acclimatized to your current altitude. Do not use Acetazolamide to push through the symptoms of altitude sickness and continue to climb, this is extremely dangerous and can be fatal. 

Acetazolamide (Diamox) side effects

The following side effects can occur when taking Acetazolamide:

  • Dizziness.
  • Lightheadedness.
  • Increased urine production.
  • Blurred vision.
  • Dry mouth.
  • Drowsiness.
  • Loss of appetite.
  • Stomach upset.
  • Headache and tiredness.

You’re most likely to develop side effects while your body is getting used to the medicine. 

Tell your doctor immediately if any of these very unlikely but serious side effects occur:

  • Increased body hair.
  • Hearing loss.
  • Ringing in the ears.
  • Unusual tiredness.
  • Persistent nausea/vomiting.
  • Severe stomach/abdominal pain.

Seek immediate medical attention if any of these unlikely but very serious side effects occur:

  • Easy bleeding/bruising.
  • Fast/irregular heartbeat.
  • Signs of infection (e.g., fever, persistent sore throat).
  • Mental/mood changes (e.g. confusion, difficulty concentrating).
  • Severe muscle cramps/pain.
  • Tingling of the hands/feet.
  • Blood in the urine.
  • Dark urine.
  • Painful urination.
  • Yellowing of the eyes/skin.

A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include:

  • Blisters/sores in the mouth.
  • Rash.
  • Itching/swelling (especially of the face/tongue/throat).
  • Severe dizziness.
  • Trouble breathing.

If you experience any adverse effects from taking Acetazolamide, inform your trip doctor immediately. In a medical emergency, contact emergency services or go straight to a hospital or medical centre.

Acetazolamide ingredients

Each tablet contains the active ingredient acetazolamide 250mg.

It also contains:

  • Lactose monohydrate
  • Corn starch
  • Gelatin
  • Glycerin
  • Water
  • Talc
  • Sodium starch glycolate type A potato
  • Magnesium stearate

Acetazolamide (Diamox) warnings

Acetazolamide is not suitable for use if you:

  • Are allergic or sensitive to or have had a bad reaction to sulphonamides in the past.
  • Are elderly.
  • Have adrenal gland problems.
  • Have chronic obstructive pulmonary disease.
  • Have closed angle glaucoma.
  • Have had kidney stones.
  • Have kidney or liver problems.

Delivery & Shipping Information

Please note that due to the current situation with COVID-19, Royal Mail are experiencing some delays. This may mean that your order takes longer to arrive than you would normally expect. We are working hard to ensure that, where possible, all orders placed before 15:00 are still dispatched the same working day.


UK Orders

We offer FREE standard tracked delivery on orders over £40.

The following delivery options are available:

  • Standard Tracked Delivery - 2 - 3 day delivery - £2.95
  • Express Tracked Delivery - 1 - 2 day delivery - £4.45
  • DPD Next Day - 1 - 2 working days - £6.95
  • Special Delivery (Guaranteed before 21:00) - £8.95
  • Saturday Guaranteed before 21:00 - £10.45

Important Delivery Information

All our orders are sent out using Royal Mail (unless stated). We always aim to dispatch all Royal Mail & DPD orders received before 15:00 the same working day. Any orders received after 15:00 or over the weekend will be dispatched the next working day. Orders will not be dispatched on weekends or bank holidays.

All orders are subject to approval by our team of doctors and pharmacists. Your delivery date in the checkout is subject to your consultation being approved by our healthcare team.

All orders can be fully tracked from your dispatch email, in your online account and from any notifications from your courier.

We ensure all parcels are in plain packaging for discreet delivery of your medicines and pharmacy goods. Where possible, we will attempt to size all parcels to fit through your letterbox in tamper-proof packaging. By placing an order on our website, you confirm that it is safe and appropriate for a package containing medicines to be posted through your letterbox, if the carrier is able to do so. You should notify our customer support team if it is not safe for the package to be posted through the letterbox, for example due to animals or small children.

Deliveries containing pharmacy-only or prescription medicines may require a signature on receipt. 

Delivery is free for all NHS prescriptions.


Royal Mail


  • Fully tracked delivery
  • SMS & email notifications
  • Four-hour delivery window
  • Change delivery date directly with Royal Mail
  • Update delivery location - add a Safeplace, preferred neighbour, or update your delivery location to a local Post Office or Royal Mail Customer Service Point.

Royal Mail are the most widely recognised mail delivery company in the UK. Being on the UK’s 29 million doorsteps six days a week means they offer unparalleled price and convenience. The Independent Pharmacy uses Royal Mail’s Tracked 48, Tracked 24, and Special Delivery Guaranteed parcel services to offer reliable, fully-tracked delivery at very competitive prices. Your Royal Mail parcel will arrive with your normal daily delivery of post.

Please note: Royal Mail do not deliver on Sundays or Bank Holidays - this should be taken into account when ordering. 

If you are not home to accept your delivery, a card should be left by the Royal Mail representative. This card will provide details of where you can collect the order or how to arrange re-delivery.

Should you be unable to collect your missed delivery or arrange for your medication to be redelivered by Royal Mail, the pharmacy can resend your medication to the same, or a different address provided it has been returned to us and this happens within a 30 day window.

Once a package has been shipped with Royal Mail we advise that you are bound to the terms and conditions of their use together with the terms and conditions contained herein.

You have the right to cancel your order up to the point when your treatment is dispatched. The pharmacist must destroy any medication within 30 days of it being returned, even un-opened boxes, so we are not able to offer refunds once your treatment has been dispatched.




  • Fully tracked delivery
  • SMS & email notifications
  • One-hour delivery window
  • Change delivery date directly with DPD
  • Update delivery location - add a Safeplace, preferred neighbour, or update your delivery location to a local collection point.

DPD Local is the most innovative parcel carrier around. Thanks to their industry-leading Predict service, they provide parcel recipients with a one hour delivery window, notified by email, so you don't have to wait in all day. What's more, it enables receivers to watch the progress of their delivery on a real-time map, all the way down to a final 15 minute time-slot. 

As well as keeping customers informed at every stage of the journey, DPD believe in maximising choice and convenience. That's why DPD provide access to a suite of options both on the day of delivery and the night before, allowing customers to take delivery of their goods in a way that suits. If you wish to reschedule, you can:

  • Select an alternative delivery date
  • Opt for delivery to a nominated neighbour
  • Have the parcel left in a specified safe place
  • Collect the parcel from your local DPD Pickup Shop
  • Upgrade delivery to By 12

Please note: DPD do not deliver on Saturdays, Sundays or Bank Holidays - this should be taken into account when ordering. 

Once a package has been shipped with DPD we advise that you are bound to the terms and conditions of their use together with the terms and conditions contained herein.

You have the right to cancel your order up to the point when your treatment is dispatched. The pharmacist must destroy any medication within 30 days of it being returned, even un-opened boxes, so we are not able to offer refunds once your treatment has been dispatched.


Forwarding houses

We are unable to ship orders to mailing or forwarding houses for onwards shipping to locations outside of the UK.


BFPO Postcodes

Unfortunately we are unable to deliver medicines to BFPO postcodes.


Remote Areas

Please be aware that Royal Mail Guaranteed services are not available to all customers in the UK, especially those that live in remote postcodes. Royal Mail advise customers of the following:

We deliver by 17:30 the next working day in the following postcode areas:
AB30 - 39, 41 - 45, 51 - 56
GY9 Alderney (Channel Islands)
HS1, 3 - 9
IV21 - 28, 40 - 49, 51 - 56
KA27, 28
KW1 - 3, 5 - 15
KW16 Stromness Town only
PA20 (0&9)
PA28 - 38, 41 - 49, 76, 77
PH15, 17 - 26, 31 - 40, 49, 50


We deliver within two working days by 17:30 to the following postcodes areas:
GY1 Herm (Channel Islands)
GY9 Sark (Channel Islands)
PA60 - 75, 78
ZE2, 3


We deliver within three working days by 17:30 to the following postcode areas:
KW16 - non-Town
PH30, 41 - 44


Please note: This applies to our 'Special Delivery' and 'Saturday Guaranteed' services.


International Orders

We are currently unable to ship orders outside of the UK.

We are unable to ship orders to mailing or forwarding houses for onwards shipping to locations outside of the UK.

Need to know more about Altitude Sickness?

Visit our advice area or contact our support team

Acetazolamide 250mg Tablets Reviews

Unsure about a treatment?
Ask our medical team for impartial information and advice about any treatment we provide or medical condition that we treat before you buy.

Frequently Asked Questions

  • How does Acetazolamide work?

    Acetazolamide is a prescription medicine known as a diuretic, which means it increases the production of urine, thus promoting the excretion of water from the body. Through inhibiting an enzyme in the body called ‘carbonic anhydrase’, it slows down certain chemical reactions in the body, changing the acidity of the blood. The net result of this is an improvement in breathing and a reduction in fluid around the brain and in the lungs. It is very important to drink a lot of fluid whilst taking Acetazolamide; at least two to three litres of water per day.


  • Can I keep climbing if I take Acetazolamide?

    Taking Acetazolamide for initial symptoms should not be viewed as a green light to keep climbing. Ascent should cease until the symptoms have completely resolved, which in most cases will be within 48 hours. Acetazolamide will not protect you against your symptoms worsening if you continue to ascend; plenty of climbers who have done this have gone on to develop either HAPE or HACE.

  • Will Acetazolamide protect me from altitude sickness if I take the tablets during rapid ascent?

    Acetazolamide will help reduce the risk of altitude sickness on rapid ascents, but it is not a substitute for following proper protocols and correct precautions. Rapid ascents carry serious risks and Acetazolamide does not remove them. In fact, it can make climbers feel safe enough to push through their illness, leading to much more severe conditions. When altitude sickness strikes, it may be sudden, severe and possibly fatal.

  • I’m really fit and strong, so is altitude sickness still a threat?

    Treat altitude with respect and do not imagine that you can simply battle through because you are strong and fit. People who climb and hike in high places have a reputation for pushing themselves. When it comes to altitude, preparation, planning ahead, taking one’s time and listening to one’s own body are the key to safety.

  • Can Acetazolamide mask a severe underlying condition, leading to complications?

    Acetazolamide does not mask serious underlying symptoms; the medication treats the cause not the symptoms. Acetazolamide accelerates acclimatisation. As acclimatisation occurs, the symptoms will resolve. Acetazolamide does not mask anything; if you are still unwell then your symptoms will persist despite the medication.

  • Will my symptoms get worse if I stop using Acetazolamide?

    If you feel better when you are taking Acetazolamide, it is because your underlying condition has improved. If you stop taking Acetazolamide, your acclimatisation will slow down to its natural rate, enabling you to gauge how well your recovery is progressing.

  • What are the benefits of Acetazolamide tablets?

    Even in its mildest form, altitude sickness can have a very negative impact on what should otherwise be an enjoyable experience. In severe cases, it can put your health at serious risk, sometimes even requiring hospitalisation. Acetazolamide tablets can help to prevent issues caused by altitude sickness or mountain sickness, provided they are used in conjunction with appropriate precautionary measures such as acclimatisation.

  • Are Acetazolamide tablets suitable medication for me?

    Acetazolamide is classed as a ‘sulphonamide derivative’ so if you are sensitive tosulphonamides, you should not take this medication. There are other conditions and some prescription drugs which are not compatible with Acetazolamide, so be sure to consult a doctor and understand the warnings before taking it.

  • Can I take Acetazolamide tablets and still drink alcohol?

    Yes you can drink alcohol whilst taking Acetazolamide tablets but it is not advisable if you are experiencing the symptoms of altitude sickness. Alcohol can make the symptoms of altitude sickness worse.

  • Can I drive whilst I am taking Acetazolamide tablets?

    Yes you can drive and take Acetazolamide tablets, however if you notice any adverse reactions or side effects, you cease taking the medication and discuss the symptoms with your doctor.

  • Can I buy Acetazolamide tablets over the counter?

    Acetazolamide is a prescription-only drug, so you cannot buy it over the counter before going on holiday. You must allow enough time to make an appointment with your GP ahead of time, or use our online service which can issue you with a doctor-verified prescription based on your responses to our health questionnaire.

  • How do I store Acetazolamide tablets?

    Acetazolamide tablets come in a handy 250mg size making them very easy to store and take whilst on the move. It is recommended that you store the tablets in a safe and secure environment at a temperature below thirty degrees centigrade, preferably at room temperature. Always keep Diamox tablets out of the reach of children.

  • Is Acetazolamide the same as Diamox?

    Acetazolamide used to be sold as Diamox, but the Diamox brand was discontinued. Since acetazolamide was the active ingredient in Diamox tablets, it was rebranded as Acetazolamide.

  • Who manufactures Acetazolamide?

    Acetazolamide is manufactured by Mercury Pharmaceuticals Ltd., Capital House, 85 King William Street, London EC4N 7BL, UK.

Authored By:

A photo of  Andy Boysan

Andy Boysan


Published on: 02-02-2017

Last modified on: 05-02-2021

Andy is a co-founder, the superintendent pharmacist and director at The Independent Pharmacy.

Reviewed By:

A photo of  Scott McDougall

Scott McDougall


Reviewed on: 05-02-2021

Next review date: 05-02-2023

Scott is one of the two founders of The Independent Pharmacy. He is a registered pharmacist and the registered manager of our service with the CQC.

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