Inca Trail Altitude Sickness — Prevention & Treatment

Why altitude matters on the Inca Trail

At sea level, atmospheric pressure is 760 mmHg. At Cusco (3,400 m), pressure has dropped to roughly 510 mmHg — about 67% of sea level. At Dead Woman's Pass (4,215 m), pressure is 460 mmHg, or 60% of sea level. This means each breath you take contains roughly 40% less oxygen than your body is used to.

Your body responds in stages: heart rate increases, breathing becomes deeper and faster, and over 1–3 days the kidneys produce more red blood cells to carry oxygen. This adaptation process is called acclimatization. Until it's mostly complete, your body is in oxygen debt — and Acute Mountain Sickness (AMS) is your body's way of telling you it hasn't caught up yet.

Recognizing altitude sickness

AMS exists on a spectrum. Here's how Cusco-based emergency physicians categorize it:

Acclimatization: the only thing that actually works

The single most effective prevention against altitude sickness is gradual ascent. Specifically:

The recommended Cusco acclimatization schedule

• Day 1 in Cusco (arrival day): Take it very easy. Walk slowly from your hotel to the Plaza de Armas, drink coca tea, eat lightly. Avoid alcohol, heavy meals and physical exertion. Sleep early. Most people feel a mild headache this evening.
• Day 2 in Cusco: Light city walking. Visit the Cathedral, museums, Qorikancha. Stay hydrated (3+ liters of water). Continue to avoid alcohol. Eat normal meals.
• Day 3 in Cusco: A short hike — Saqsayhuamán above the city, or descend to the Sacred Valley (lower altitude, around 2,800 m, which actually helps). This tests how your body responds to mild exertion at altitude.
• Day 4 (or later): Start the trek. By now, your body has begun producing additional red blood cells, your breathing pattern has adapted, and Day 1 of the trail (which only reaches 3,000 m) should feel manageable.

If you only have 1 night in Cusco before the trek, you are taking a real risk. Many travelers manage it, but the rate of significant AMS roughly doubles compared to a 3-day acclimatization.

Diamox (acetazolamide): does it work?

Yes, with caveats. Acetazolamide accelerates the kidneys' acid-base adjustment to altitude, effectively making your body think it's higher than it is, which speeds adaptation. Standard prophylactic dose: 125 mg twice daily, started 24 hours before reaching altitude, continued for 3 days at altitude.

Side effects (common, usually mild):

• Tingling in fingers, toes and lips (paresthesia)
• Increased urination (Diamox is a diuretic — drink more water)
• Carbonated drinks taste flat (literally affects how taste buds detect CO₂)
• Mild fatigue

You must consult your own doctor before taking Diamox. It is contraindicated for people allergic to sulfa drugs and may interact with other medications. Some doctors prescribe it routinely for high-altitude travel; some prefer to reserve it for symptomatic treatment. Both approaches are reasonable.

Coca tea and traditional remedies

Coca tea (mate de coca) is widely served in Cusco and offered freely at trail campsites. Cusco residents and many trekkers swear by it for managing mild altitude symptoms. The pharmacology is real but mild: chewing or steeping coca leaves releases small amounts of alkaloids that mildly increase heart rate and may help with mild headache and nausea.

Coca is legal in Peru. It is not the same as cocaine, which requires industrial processing of the leaves. However, coca leaves and coca tea will trigger drug tests for several days after consumption — relevant if you face workplace testing on return. Coca is also generally illegal to take across international borders.

Hydration and food at altitude

• Water: Aim for 4 liters per day during the trek (more than at sea level). The dry mountain air dehydrates faster than you realize.
• Carbohydrates: Your body uses glucose more efficiently than fat at altitude. Loading up on rice, potatoes, pasta, fruit and energy bars is genuinely useful.
• Avoid alcohol for the first 48 hours at altitude and the entire trek. Alcohol exacerbates dehydration and impairs sleep recovery.
• Avoid heavy meals right before high-altitude exertion. Digestion competes with muscles for blood flow.
• Electrolytes: Salt, potassium and magnesium are lost through increased breathing rate. Electrolyte tablets or oral rehydration salts are useful.

What if symptoms become serious?

Every licensed Inca Trail guide carries:

• A small oxygen tank (1–2 liter capacity)
• A pulse oximeter to measure blood oxygen saturation
• Basic first aid kit including ibuprofen and dexamethasone (for severe HACE)
• A radio for emergency coordination with SERNANP

If you develop moderate to severe symptoms, your guide will:

1. Stop the trek and assess your oxygen saturation
2. Administer supplementary oxygen if SpO₂ < 75%
3. If symptoms don't improve in 1–2 hours, organize descent — typically with a porter escort to the nearest exit point (Wayllabamba on Day 1–2, Lucmabamba on Day 3, Aguas Calientes on Day 4)
4. For HACE/HAPE: emergency helicopter evacuation if descent is too slow. This is why mandatory altitude-trekking insurance was introduced for 2026.

Who is at higher risk?

Some factors increase the likelihood of significant AMS:

• Living at sea level (compared to people from already-high regions)
• Faster ascent rate (single-night Cusco stop before trek)
• Younger age, paradoxically — younger trekkers tend to push harder and ignore early symptoms
• Previous history of altitude sickness (it tends to recur)
• Dehydration, alcohol use, smoking
• Some pre-existing conditions (heart, lung, blood disorders)

If you have a history of heart disease, severe asthma, or pulmonary hypertension, consult an altitude-medicine specialist before booking the trek. The Short Inca Trail (max 2,720 m) is a much safer alternative for most cardiopulmonary conditions.