Altitude Sickness: Using Acetazolamide for High-Altitude Travel (UK Guide)

Altitude sickness, medically referred to as Acute Mountain Sickness (AMS), is a collection of symptoms that occur when you ascend too quickly to elevations above 2,500 metres. At these heights, the air pressure is lower, and there is less oxygen available with every breath. This puts a significant strain on the body as it attempts to maintain oxygen saturation in the blood.

In the UK, many travellers encounter this condition when visiting destinations such as the Alps, the Andes, or high-altitude regions in Nepal and Africa. While mild AMS is common and often manageable, it is essential to recognise the signs early to prevent progression to life-threatening complications. Natural acclimatisation—the process where the body increases red blood cell production—takes time, usually several days, which is why rapid ascent is the primary risk factor.

Most British travellers describe altitude sickness as feeling like a severe hangover. These symptoms typically develop within 6 to 24 hours of reaching a higher altitude. According to NHS guidance, you should be aware of the following signs:

• Headache: Usually throbbing and worsened by exertion.
• Nausea and Loss of Appetite: Feeling sick or being unable to eat properly.
• Dizziness and Light-headedness: Feeling unsteady on your feet.
• Fatigue: Feeling unusually tired or weak, even after resting.
• Disturbed Sleep: Difficulty falling asleep or waking up frequently during the night.
• Shortness of Breath: Generally felt upon mild exertion, such as walking up a small incline.

If you experience these symptoms, the golden rule of travel health is to not ascend any further until the symptoms have completely resolved. Continuing higher while symptomatic significantly increases the risk of severe illness.

Acetazolamide (standardly prescribed in the UK under the brand name Diamox) is a carbonic anhydrase inhibitor. While it is not a licensed treatment for altitude sickness in all territories, it is widely recommended by the National Institute for Health and Care Excellence (NICE) and travel health specialists for the prevention of AMS in high-risk scenarios.

How does it work?

Acetazolamide works by increasing the amount of bicarbonate excreted in the urine. This makes the blood slightly more acidic, which stimulates the brain to increase the rate and depth of breathing. This 'extra' breathing increases the amount of oxygen in the blood, effectively speeding up the natural acclimatisation process. It is important to note that acetazolamide is a preventative measure, not a substitute for a safe ascent rate.

Treatment Regimen

For most UK travellers, the typical preventative dose involves starting the medication one or two days before you begin your ascent and continuing it for at least two days after reaching your peak height. As this is a prescription-only medication in the UK, a clinical assessment by a doctor is required to ensure it is safe for you to take, particularly if you have allergies to sulfonamides (sulfa drugs).

Medication is only one part of staying safe at high altitudes. Following established safety protocols is essential for a successful trek:

• Fly high, sleep low: If possible, spend a few days at a moderate altitude (around 1,500m-2,000m) before moving higher.
• Gradual Ascent: Once above 3,000m, increase your sleeping altitude by no more than 300 to 500 metres per day.
• Rest Days: Schedule a rest day for every 600m to 900m of ascent to allow your body to catch up.
• Hydration: Drink plenty of water. Dehydration can mimic and worsen AMS symptoms.
• Avoid Alcohol: Alcohol is a respiratory depressant and can interfere with acclimatisation and sleep.
• Eat Carbs: A diet high in carbohydrates is less demanding on the body’s metabolism at altitude.

Planning a trip to high-altitude regions can be complex, and seeking professional advice before you depart is highly recommended. You should consider booking a consultation with a UK online doctor if:

• You have a pre-existing medical condition, such as heart or lung disease, that may be affected by lower oxygen levels.
• You are planning to travel to an area above 3,000m and wish to discuss the suitability of acetazolamide for your itinerary.
• You have experienced altitude sickness in the past and want to develop a preventative strategy.
• You need a prescription for travel-related medications and cannot easily visit your local GP surgery before your flight.

An online GP can review your medical history, discuss the risks of your specific destination, and provide a prescription for medication if appropriate, all from the comfort of your home. This ensures you have the necessary supplies in your travel kit before you leave the UK.

While AMS is generally mild, it can occasionally progress to two life-threatening conditions. These require immediate medical intervention and descent:

High Altitude Pulmonary Oedema (HAPE)

This is a build-up of fluid in the lungs. Symptoms include a persistent cough (sometimes with frothy, pink spit), extreme breathlessness even at rest, and a bluish tint to the skin (cyanosis). This is a critical medical emergency.

High Altitude Cerebral Oedema (HACE)

This is a build-up of fluid on the brain. Symptoms include severe confusion, ataxia (stumbling like a person who is intoxicated), and a loss of consciousness. If a person displays signs of confusion or poor coordination at altitude, they must be moved lower immediately.