Altitude Sickness Prevention: Using Acetazolamide for High-Altitude Travel

Altitude sickness, medically referred to as Acute Mountain Sickness (AMS), is a condition caused by rapid exposure to low amounts of oxygen at high elevations. It commonly affects British travellers heading to destinations such as the Alps, the Andes, the Himalayas, or Mount Kilimanjaro. While most cases are mild, the condition can progress to life-threatening complications if ignored.

As you climb higher, the atmospheric pressure decreases, meaning there are fewer oxygen molecules in every breath you take. Your body requires time to adjust to these changes through a process called acclimatisation. If you ascend faster than your body can adapt, you may experience a range of debilitating symptoms. According to NHS guidance, symptoms usually start within 6 to 24 hours of reaching an altitude above 2,500 metres.

Common Symptoms

Many travellers describe altitude sickness as feeling like a massive hangover. The symptoms are often non-specific but typically include:

• A persistent, throbbing headache (usually the first sign).
• Nausea or vomiting.
• Loss of appetite.
• Dizziness or light-headedness.
• Fatigue and weakness.
• Disturbed sleep or insomnia.
• Shortness of breath during mild exertion.

If you experience these symptoms while trekking, the golden rule of mountain safety is to stop ascending. You should remain at your current altitude until symptoms resolve or descend if they worsen.

The most effective way to prevent AMS is a gradual ascent—climbing no more than 300 to 500 metres per day once above 3,000 metres. however, for those with a history of altitude issues or those on fixed trekking itineraries, medication may be helpful. In the UK, acetazolamide (sometimes referred to by the brand name Diamox) is frequently prescribed 'off-label' for altitude sickness prevention.

How Acetazolamide Works

Acetazolamide is a carbonic anhydrase inhibitor. It works by increasing the amount of bicarbonate excreted in the urine, which makes the blood slightly more acidic. This acidity mimics the presence of CO2, tricking the brain into thinking there is a surplus of carbon dioxide. In response, the body increases its breathing rate, which in turn increases oxygen intake and speeds up the natural acclimatisation process.

NICE (National Institute for Health and Care Excellence) guidelines suggest that acetazolamide can be considered for travellers at moderate to high risk of AMS. It is typically started 1 to 2 days before reaching high altitude and continued for at least two days after reaching the highest point.

If you are planning a trip to a high-altitude region, it is essential to seek professional medical advice at least 4 to 6 weeks before you depart. Since acetazolamide is a prescription-only medication in the UK, you cannot buy it over the counter at a pharmacy.

You should consult an online GP to:

• Assess Your Risk: A doctor will review your itinerary and health history to determine if you are at high risk of AMS.
• Discuss Suitability: Acetazolamide is a sulfonamide derivative; therefore, it may not be suitable for people with certain allergies or kidney conditions.
• Obtain a Prescription: If appropriate, our online GP service can provide a prescription for preventative treatment, which can be delivered to your home or collected at a local UK pharmacy.
• Receive Customised Advice: Get tailored guidance on hydration, ascent rates, and what to do if you encounter red-flag symptoms abroad.

While acetazolamide is generally well-tolerated, it is a medication and can cause side effects. It is important to be aware of these so you do not mistake them for altitude sickness itself. Common side effects include:

• Tingling or 'pins and needles' (paresthesia) in the fingers, toes, or face.
• Increased frequency of urination (as the drug is a mild diuretic).
• Changes in taste, particularly a metallic taste when drinking carbonated beverages.
• Occasional nausea or blurred vision.

It is often recommended to take a 'trial dose' for two days while still in the UK to ensure you do not experience any adverse reactions before you are in a remote mountain environment.

Medication should never be used as a substitute for proper acclimatisation. To stay safe, follow these evidence-based travel tips:

• Fly high, sleep low: If you must fly into a high-altitude city (like La Paz or Cusco), take it very easy for the first 48 hours.
• Stay Hydrated: Altitude increases fluid loss through breathing and urination. Drink plenty of water but avoid alcohol, which can exacerbate symptoms and mask signs of AMS.
• Eat Carbohydrates: Low oxygen levels change how your body processes energy; a high-carb diet is often easier to digest and provides necessary fuel.
• Don't over-exert: Keep your pace slow and steady. If you are gasping for breath while talking, you are moving too fast.