Altitude Sickness on a Road Trip: How to Drive High Safely

Almost everything written about altitude sickness is aimed at people who just landed in Cusco or La Paz. But if you're going by car, you're in a different situation, and a better one: a plane drops you up high with no say in the matter, while a car hands you the clock. You decide how many meters you climb each day and, above all, where you stop to sleep.

That decision is exactly what every recommendation in altitude medicine is built on.

In short: Altitude sickness starts to show up from a sleeping altitude of 2,400 to 2,500 meters, and it affects about a quarter of people who climb into that range. The first symptom is always a headache. The prevention that works is pacing: above 3,000 meters, don't raise the altitude you sleep at by more than 500 meters a day. Drinking water doesn't prevent it. Physical fitness doesn't protect you. And the signal to descend is any neurological change or shortness of breath at rest.

Who gets it, and from what altitude

The risk starts at around 2,400 to 2,500 meters of sleeping altitude. In that range, about a quarter of people develop some symptom. Above 3,350 meters with a fast ascent, the incidence rises to 30% to 40%.

Symptoms usually appear 6 to 12 hours after the ascent, often during or right after the first night, and go away in 24 to 48 hours if you don't climb any higher. The mild form is defined quite objectively in the literature: a headache, plus at least one of loss of appetite, dizziness, fatigue and nausea. The comparison the CDC itself uses is a good one: it feels like a hangover.

Two common beliefs fall apart here. Physical fitness doesn't protect you, and there are clinical sources saying it may even raise the risk, probably because fit people push harder in the first few hours. And older age is not a risk factor: over 50 the risk is slightly lower, and sex makes practically no difference. What raises the risk is having been sick before, living close to sea level, climbing too fast and, above all, sleeping high.

The rule that organizes everything

Every acclimatization guideline is written in terms of sleeping altitude, never the highest altitude you reached during the day. This isn't a detail, it's the core:

• Above 3,000 meters, don't raise the altitude you sleep at by more than 500 meters a day. Some guidelines start applying the rule as low as 2,500 meters.
• Don't sleep above 2,750 meters on the first day coming from low altitude.
• One extra acclimatization night for every 1,000 meters gained in sleeping altitude.

And that leads to the principle that sums it all up, which appears under that name in clinical material: climb high, sleep low. You can cross a pass at 4,200 meters at two in the afternoon and sleep at 2,400 meters at eight at night. For someone who arrived by plane, doing that means hiring transportation. For you, it just means keep driving.

Why this is an advantage, and why it's not a guarantee

A review of more than 11,000 people showed that incidence rises 4.5 times faster when the ascent is by plane than by land. Flying straight to 3,740 meters, 84% of people develop symptoms. The cause the authors point to is time: the plane gives the body no window to adjust.

But a car is not a free pass, and there's a study that proves it in an uncomfortable way. When a new road opened in the Nepalese Himalayas linking 760 meters to 3,540 meters, the local clinic recorded the highest number of cases of all the seasons compared: more than half of the patients arrived by vehicle, and a third left low altitude and arrived in less than 48 hours.

In other words, a car is not safer than a plane. A car is the only vehicle that puts the pace in your hands, and what decides the outcome is whether you use it.

A concrete stretch helps. From San Pedro de Atacama, at 2,407 meters, to Paso de Jama, at 4,200 meters, it's almost 1,800 meters of gain in one afternoon. Three and a half times the 500 meter rule. But the rule is about where you sleep, and nobody sleeps on the pass. The same goes for the climb to Salinas Grandes and Hornocal, in the Quebrada de Humahuaca, and for the crossing of southwestern Bolivia to the Salar de Uyuni, which spends entire days above 4,000 meters.

What doesn't prevent it

This part saves you money and frustration.

Water doesn't prevent altitude sickness. Staying hydrated keeps your performance up and stops you from feeling worse, but it doesn't lower your chance of getting it, and forced overhydration doesn't work. Drink well because you lose more fluid at altitude, just don't confuse that with prevention.

The oxygen cans sold at gas stations and hotels won't fix it. Therapeutic oxygen improves a headache in about half an hour, but at a flow of 1 to 2 liters per minute. A portable can holds 5 liters at most. Do the math and you get a few minutes.

What actually helps, besides pacing: no alcohol and no heavy exertion in the first 48 hours, and no sedatives or anything else that depresses breathing. One counterintuitive detail: if you drink coffee every day, keep drinking it, because a caffeine withdrawal headache looks exactly like the main symptom of altitude sickness.

Signs that it has turned serious

Here the tone changes, and for good reason. The mild form is uncomfortable. The two severe forms are emergencies.

Cerebral edema. What sets it apart is not how bad the headache is, it's the appearance of a neurological sign. The most reliable and earliest one is an unsteady gait, walking as if you'd been drinking. Then come mental confusion and abnormal drowsiness. The CDC describes the condition as resembling drunkenness. Without treatment, 12 to 24 hours can pass from the first stagger to coma.

Pulmonary edema. It appears 24 to 96 hours after a fast ascent. It starts with shortness of breath out of proportion to the effort and lower exercise tolerance, progresses to shortness of breath at rest and, in the advanced stage, pink or bloody sputum. It accounts for most deaths from altitude illness.

In both cases, there's only one course of action: descend. Oxygen and medication buy time, but they don't replace descending and shouldn't delay it. A descent of 300 meters already improves the mild form quickly; for a severe case, the reference is 300 to 500 meters.

This is where the car stops being a convenience and becomes emergency equipment. On the Bolivian altiplano the nearest care can be three or four hours away by car, and air rescue has its own limitations: many air ambulance services can't land in La Paz because of the altitude. When you buy travel insurance, check that the policy covers evacuation from high altitude.

Driving with symptoms

Honesty is called for here, because the evidence doesn't all point the same way. Simulator studies haven't shown that mild hypoxia alone significantly worsens driving. But three solid facts add up.

The severe form is indistinguishable from drunkenness, and the early sign is an unsteady gait, which someone sitting behind the wheel won't notice. Aviation medicine works with night vision deteriorating from as low as 1,500 meters and with impaired judgment and coordination between 3,650 and 4,570 meters, a range that squarely covers the Andean passes. And in simulators, neither alcohol alone nor hypoxia alone impaired performance at the levels studied, but the combination of the two did, with a clear effect on reaction time and fine coordination.

Put together: driving at night, at altitude, with symptoms, after a beer at dinner brings together every documented factor at once.

Your car feels it too, and less than you do

A naturally aspirated engine loses about 3% of its power for every 305 meters of altitude, a rule published by engine and turbo manufacturers. At the top of Paso de Jama that comes to nearly 40% less: a 150 hp engine delivers the equivalent of about 90 hp. Nothing breaks, but it calls for a lower gear, patience on the climb and no optimistic passing. A turbo reduces that loss because it compresses the air, but there's no manufacturer figure saying how much it recovers, and there's a technical document applying the same deduction to turbo engines. Count on less power either way.

If your route includes the big passes, the guide to crossing the Andes by car covers the border side that this article doesn't.

About coca tea

Two pieces of information that rarely appear together. The first is that there's no efficacy study of coca for altitude sickness, and no reference clinical guideline mentions it among prevention measures. In a survey of travelers, 51% reported no noticeable effect.

The second is legal and applies to every Brazilian heading home: coca leaf is on Anvisa's list of prohibited plants, which expressly bans importing, selling and using it. Drinking tea in Cusco is one thing, crossing the border with the package in your backpack is another. And consumption leaves a marker detectable in a urine test for up to 24 hours, which matters for professional drivers.

Frequently asked questions

At what altitude does altitude sickness start?

At around 2,400 to 2,500 meters of sleeping altitude. Below that it's uncommon. The altitude that counts is the one where you spend the night, not the highest point of the day.

What are the symptoms?

Always a headache, along with at least one of loss of appetite, nausea, dizziness, fatigue and poor sleep. They appear 6 to 12 hours after the ascent and go away in 24 to 48 hours if you don't climb any higher.

What should you do when it hits?

Stop climbing and rest. If you feel better, continue the next day. If it gets worse even at rest, descend. And if any neurological sign appears, such as an unsteady gait or confusion, or shortness of breath at rest, descend immediately and seek medical care.

Does drinking a lot of water help?

It helps your performance and well-being, because you lose more fluid at altitude. But it doesn't prevent altitude sickness. Prevention is the pace of your ascent.

Can altitude sickness kill, and can you take preventive medication?

In severe cases, yes, it can. High altitude pulmonary edema accounts for most deaths from altitude illness, and the mild form is the warning that you climbed too fast. As for preventive medication, there are drugs used for that purpose, and that's a conversation to have with a doctor before the trip, ideally at a travel medicine clinic. It's not something to sort out at a roadside pharmacy.

Planning is the remedy

What altitude medicine asks for is almost mundane: climb slowly and sleep low. What makes this hard for most people is not having control over their own itinerary. You do. Every night of your trip is your choice, and that choice, not the altitude of the pass, decides how your body will react. Plan your route by the altitude of your beds, not your viewpoints.

This article brings together information from reference clinical sources and does not replace a medical evaluation. If you have a preexisting health condition or have been sick at altitude before, talk to a doctor before you go up.