Cusco Altitude: How to Acclimatize

The first flight out of Lima lands in Cusco a little after half past seven in the morning. In roughly eighty minutes of flying you have gone from sea level to 3,400 m. By ten you are sitting in the Plaza de Armas with a coffee, feeling faintly strange but basically fine, and a tour desk is offering you Rainbow Mountain — 5,036 m — for the day after tomorrow. The Cusco altitude problem is really an itinerary problem. The city is high enough to make a meaningful number of visitors ill, and low enough that almost everybody adapts within a couple of days. What goes wrong is the gap between those two facts, and the fact that the standard Peru trip sells you a 5,000 m day out about 36 hours after you arrive. Sequencing the excursions out of Cusco by altitude rather than by scenery removes most of the problem.

This is the article I wish someone had handed me before my first trip. It leans on the actual guidance — the CDC Yellow Book chapter on high-altitude travel, the Wilderness Medical Society practice guidelines, the published research on travellers arriving specifically in Cusco — rather than on what the tour operator tells you while selling the tour.

What the Cusco altitude numbers actually mean

Cusco sits at about 3,400 m (11,150 ft). You will see 3,399 m, 3,350 m and 11,152 ft quoted in different places, and they are all roughly right: the city is built up the sides of a bowl, so the number depends on where you are standing. The Plaza de Armas is the usual reference point. The San Blas steps take you noticeably higher than that, which is why the walk back up to your guesthouse feels harder than it has any right to.

Air pressure, and therefore the amount of oxygen you get per breath, falls with altitude. The CDC puts the inspired oxygen pressure at around 3,050 m at 69% of the sea-level value. Cusco is higher again, so you are breathing air that delivers roughly two-thirds of the oxygen you are used to. Nothing is missing from the air — the proportion of oxygen is identical — there is simply less air.

The single most useful fact on this page, and the one almost nobody tells you before they have your deposit: Machu Picchu is lower than Cusco. Considerably lower.

Read that table twice before you book anything. Half the anxiety people carry about the ruins themselves is misplaced — the citadel is the easy part of the trip, physiologically. It is Cusco, Puno and the high day trips that ask something of you. If your itinerary has you sleeping in Cusco and then bussing to Vinicunca on day two, the risk is concentrated somewhere quite different from where you assumed.

Why flying LIM–CUZ breaks every rule in the guidance

The published advice on ascent is boringly consistent. Avoid going from low altitude to a sleeping altitude above about 2,750 m in a single day. Once above 3,000 m, raise your sleeping altitude by no more than roughly 500 m a night, and take an extra night for every 1,000 m gained. Those are the Wilderness Medical Society numbers, echoed in the CDC Yellow Book.

A Lima–Cusco flight is about an hour and twenty minutes. It breaks all three rules at once, and it does so before your coffee has gone cold. The Yellow Book names Cusco explicitly as one of the destinations where travellers arrive by air above 3,400 m with no adaptation at all, and puts that pattern in the high-risk category, with altitude illness rates approaching 50% when gradual or staged ascent is not possible. That is not a scare statistic. It is the baseline for what you are doing.

The counterweight is that Cusco is only 3,400 m. The human body adapts to moderate hypoxia up to about 5,200 m; the acute part of that process runs over three to five days. Cusco is comfortably inside the range where essentially everyone adapts. You are not being asked to do something exotic. You are being asked to do it faster than your body would like.

What altitude sickness in Cusco actually feels like

Acute mountain sickness (AMS) is what most people mean by soroche. The research standard is the 2018 Lake Louise score, and it is worth knowing because it is more specific than the vague lists you find on tour sites. AMS requires a headache, plus at least one of nausea or vomiting, fatigue or weakness, and dizziness or light-headedness. Each is rated 0 to 3; a total of 3 or more, with at least one point coming from the headache, counts as AMS. Three to five is mild, six to nine moderate, ten to twelve severe.

Two things about that definition matter to a traveller. First, no headache usually means no AMS — feeling puffed climbing stairs in San Blas is normal physiology, not illness. Second, the 2018 revision dropped sleep disturbance from the score, because broken sleep above about 2,700 m is close to universal and does not distinguish the ill from the fine. You will sleep badly in Cusco. That on its own is not a diagnosis.

Timing is the other giveaway. Symptoms usually appear 2 to 12 hours after arrival, very often during or just after the first night, which is why so many people describe waking on their first Cusco morning feeling like they drank far more than they did. That comparison is not a joke: the Yellow Book describes AMS symptoms as being like an alcohol hangover. If you do not go any higher, it typically settles within 12 to 48 hours and resolves over one to three days. Symptoms that begin after three days at the same altitude are almost certainly something else.

How common is it in Cusco specifically? A cohort study of foreign language students arriving in the city, published in the Journal of Travel Medicine, used the 2018 Lake Louise criteria and found 39% developed AMS in their first 48 hours — two in five. Older airport surveys using looser definitions put the figure closer to half. Either way, this is common. It is also, in the overwhelming majority of cases, self-limiting and unremarkable.

What it is not: fever, chills, muscle aches or a runny nose. Those point to a virus. Nor is it necessarily altitude at all — dehydration, a red-eye flight, a hangover from the pisco sours you had in Miraflores the night before you flew, and plain exhaustion all produce a similar first morning.

HACE and HAPE: rare at 3,400 m, but know the red flags

Two conditions sit at the serious end. Both are uncommon at Cusco’s elevation. Neither is impossible, and both kill people who ignore them.

High-altitude cerebral edema (HACE) is, functionally, end-stage AMS. It is rare below about 4,300 m. What separates it from AMS is neurology: ataxia (you cannot walk a straight heel-to-toe line), confusion, drowsiness, behaviour that looks like drunkenness in someone who has not been drinking. Untreated, coma can follow within 12 to 24 hours of the onset of ataxia. The heel-to-toe walk is the field test worth remembering, because it is objective and a confused person cannot talk their way out of it.

High-altitude pulmonary edema (HAPE) is fluid in the lungs. It can be faster to kill than HACE. It begins as chest tightness, a dry cough, and breathlessness that is out of proportion to the effort — you are gasping on a slope that your companions are walking up. It progresses to breathlessness at rest, then frank respiratory distress, often with frothy or blood-streaked sputum. Oxygen saturation drops hard: readings of 50–70% are common, at least ten points below healthy people standing next to you at the same altitude. Incidence is roughly one in 10,000 among Colorado skiers, and up to one in 100 above 4,300 m.

The rule for both is the same and it has no exceptions worth arguing about. Descend. Descent beats every drug and every gadget. From Cusco this is unusually easy: the Sacred Valley floor is 600 m lower and an hour and a half away by road, and Aguas Calientes is 1,360 m lower. You are not stuck on a Himalayan ridge waiting for weather.

It is also worth saying plainly that Cusco is a city of several hundred thousand people with hospitals, private clinics used to treating tourists, doctors who will come to your hotel, bottled oxygen and hyperbaric chambers. Serious altitude illness here is a manageable medical problem, not a wilderness emergency. Most hotels can arrange a doctor within the hour; ask reception rather than trying to find a clinic yourself at two in the morning.

Symptom triage: what to do, and when to stop discussing it

The three rules the Yellow Book distils it all into are worth memorising. Know that the early symptoms look like a hangover, and be willing to admit you have them. Never go up to sleep higher while you have symptoms, however trivial they seem. And descend if things get worse despite rest and treatment where you are.

What actually works, and what people do instead

The free things, which are also the effective things

Go up slowly. Everything else is a distant second. If you cannot go up slowly — and on the standard Peru trip you usually cannot — then structure the first 48 hours to be as easy as possible.

• Rest, genuinely. Only mild exercise for the first 48 hours. That is the guidance, not a suggestion to take it easy-ish.
• Alcohol: none for the first 24 to 48 hours. The Yellow Book says 48. Alcohol depresses breathing at exactly the moment your body needs to breathe more, and its symptoms are indistinguishable from AMS, so you cannot tell what you are dealing with.
• Water: drink enough, but do not perform. You lose more fluid than usual to dry air and faster breathing, and dehydration will make you feel dreadful. But dehydration does not cause AMS and drinking four litres will not prevent it. Aim to keep your urine pale. Forcing water past that point risks diluting your sodium, which produces symptoms that look exactly like altitude illness.
• Eat light and carbohydrate-heavy. Soup, bread, rice, potatoes. Peru gives you several thousand varieties of potato to work with, so this is no hardship. Save the ambitious Peruvian food for day three.
• Keep your coffee. If you drink caffeine daily, keep drinking it. Caffeine withdrawal produces a headache you will misread as altitude.
• No sedatives. Sleeping pills, opiate painkillers and anything that depresses breathing are a bad idea at altitude.

Acetazolamide (Diamox), described properly

Acetazolamide is the only drug most travellers to Cusco should be thinking about, and it is the one thing in this article that genuinely moves the odds. In that Cusco cohort study, it was the only preventive measure associated with a lower risk of AMS.

What it does: it inhibits carbonic anhydrase, producing a bicarbonate diuresis and a mild metabolic acidosis. That acidosis pushes you to breathe more, which raises your blood oxygen, particularly while asleep. In effect it compresses the three-to-five days of ventilatory acclimatisation into about one. It does not mask symptoms. It speeds up the adaptation itself.

Dosing, per the Wilderness Medical Society and the CDC: 125 mg every 12 hours, starting the day before you ascend and continuing for the first two days at altitude, longer if you are still going up. For high-risk ascent profiles, 250 mg twice daily is an option worth discussing with a prescriber. A larger trial found 62.5 mg was less effective than 125 mg, so halving the low dose to dodge side effects is a false economy.

The side effects nobody warns you about, in order of how often people complain:

• Tingling in fingers, toes, lips and face. Harmless, common, and startling if you were not expecting it.
• Frequent urination. It is a diuretic. Plan around long bus journeys and overnight trains accordingly.
• Fizzy drinks taste wrong. Flat, metallic, strange. This is a direct and rather elegant consequence of the drug: carbonic anhydrase normally breaks down carbon dioxide on your tongue, so with it inhibited you taste the CO₂ itself. Beer is a casualty. You should not be drinking beer anyway.

On the sulfa question, which travel forums get wrong constantly: acetazolamide is a sulfonamide derivative, but it is a non-antimicrobial one, and the CDC states that cross-sensitivity between sulfa antibiotics and acetazolamide has not been reported. A sulfa antibiotic allergy is therefore not, by itself, a reason to rule it out. What does warrant caution is a history of anaphylaxis to any drug, or multiple drug allergies. That is a conversation for a prescriber, not a forum.

Two practical notes. It is prescription-only, so get it before you fly — and in the UK it is not licensed for altitude illness, meaning your GP or travel clinic prescribes it off-label, which some are more comfortable doing than others. And while pharmacies in Cusco sell it readily over the counter, the sensible time to make this decision was a fortnight earlier at a travel clinic.

Dexamethasone, ibuprofen and the rest

Dexamethasone treats moderate to severe AMS and HACE, typically 4 mg every six hours, and it is normally used as an adjunct to descent rather than instead of it. It is a treatment drug administered by clinicians, not something a tourist should be self-medicating with in a hotel room. It masks nothing and cures nothing about the underlying hypoxia, and stopping it at altitude before you have acclimatised can produce rebound symptoms.

Ibuprofen 600 mg every eight hours has reasonable evidence for preventing AMS — less effective than acetazolamide, but cheap, over the counter and well tolerated. For a plain altitude headache, ibuprofen 600 mg or paracetamol 500 mg every eight hours is the standard answer. Nifedipine and tadalafil prevent HAPE and are reserved for people with a known susceptibility, prescribed in advance.

Sorojchi pills, on sale in every pharmacy on Avenida El Sol, are an analgesic combination rather than an acclimatisation drug. They will take the edge off a headache. Read the label against anything else you are taking so you do not double up on painkillers.

This is general travel information, not medical advice. Altitude medication interacts with existing conditions and other drugs. Talk to a travel-medicine clinic or your own doctor before you go, particularly if you take anything regularly or have a heart, lung or kidney condition.

Coca tea, muña and oxygen bars: what the evidence says

Coca is woven into daily life in the Andes and has been for millennia. Your hotel will have a jug of mate de coca in the lobby. Drivers chew leaves. Offering coca is a courtesy. None of that is in question, and drinking it is not some tourist affectation — it is simply what people do here.

What the evidence does not support is the claim that it prevents altitude sickness. That same Cusco cohort found that 34% of arrivals drank coca leaf tea specifically to prevent AMS — more than took any medication — and that it was not associated with any reduction in risk. The Wilderness Medical Society’s position is that coca should not be substituted for measures that are known to work.

That does not mean it is useless. A cup contains a small amount of coca alkaloid, roughly comparable in effect to a coffee, and plenty of people find it settles a queasy stomach and takes the edge off a headache. Symptom relief and prevention are different things. Drink it because it is pleasant and because it is what is in front of you. Do not let it replace an empty afternoon.

Two warnings that matter more than the physiology:

• It will show up on a drug test. A single cup produces benzoylecgonine concentrations far above the standard 300 ng/mL screening cut-off, and it can remain detectable for a day or more. If your employer tests, or you are a competing athlete, skip it entirely. The Peruvian footballer Paolo Guerrero’s 2017 doping case turned on precisely this.
• Do not take it home. Coca leaf and coca tea bags are legal in Peru and Bolivia and controlled almost everywhere else — Schedule II in the United States. Customs seizures are not a theoretical risk. Finish the box before you fly.

Muña, the Andean mint you will be offered alongside coca, is pleasant and warming and has no evidence behind it either. Drink it because you like it.

Canned oxygen and oxygen bars deserve a blunter answer. The little pressurised cans hold at most about five litres of oxygen — a few minutes of relief, and nothing that changes your adaptation. A two-minute session at an oxygen bar is the same thing with a lounge attached. Sustained low-flow oxygen at 1–2 litres a minute is genuinely effective: it clears an altitude headache in about half an hour and resolves AMS symptoms over a few hours, and it is what hotels with oxygen-enriched rooms and clinics with cylinders are actually providing. The distinction is between hours of oxygen and a novelty inhaler. Pay for the first, not the second.

Your first 72 hours: a plan that works

Assume you have flown in from Lima. The aim is not to feel nothing. It is to have nothing worse than mild symptoms, so you never lose a day or need a doctor.

1. Day 0, morning: take the earliest flight you can get. Land, transfer, drop your bags. If your hotel cannot check you in, ask them to hold the room and doze in the lounge. Sleep if you slept badly the night before.
2. Day 0, afternoon: nothing. Deliberately, boringly nothing. Walk the Plaza de Armas slowly, sit in a café, watch the city. This is the single highest-value decision on the whole trip and it costs you nothing but an afternoon.
3. Day 0, evening: eat early and light. No alcohol. Expect to sleep badly and do not be alarmed by it.
4. Day 1: flat, low-effort sightseeing. Qorikancha, the cathedral, the San Pedro market, a museum. Keep to the more sedate things to do in Cusco and leave the uphill for tomorrow. If you have a headache, this is a rest day, not a compromise day.
5. Day 2: the first proper exertion. Sacsayhuamán above the city, or a Sacred Valley day trip, which conveniently spends most of its time lower than Cusco.
6. Day 3: Machu Picchu. You are going downhill, which is the right direction. If you are trekking instead, this is the earliest sensible start.
7. Day 4 or later: anything above 4,500 m. Rainbow Mountain, Humantay, Ausangate, Palccoyo. Not before.

The thing worth defending hardest on that list is the empty first afternoon. Every itinerary I have seen sold with a “free afternoon to acclimatise” quietly fills it with a city tour by the time you arrive. Say no. Push the tour to day one. It changes nothing about what you see and a great deal about how you feel for the rest of the week.

The Sacred Valley strategy: when the transfers are worth it

The best-known workaround is to skip Cusco on arrival and drive straight down to the Sacred Valley — Urubamba at around 2,870 m, Ollantaytambo at around 2,790 m — sleep there for two nights, and come up to Cusco later. The CDC endorses exactly this logic for Cusco and La Paz: travellers can descend below the airport to sleep for one or two nights before beginning their ascent, potentially removing the need for medication altogether. How that plays out over a whole trip is worked through in our answer to how many nights Cusco actually needs.

Six hundred metres sounds trivial. It is not. Sleeping altitude is what drives altitude illness, hypoxaemia is worst at night, and the valley is also warmer, greener and dramatically more pleasant to spend a first day in.

It is worth it if:

• You have two or more nights to give it. One night is not worth three hours in a car.
• You are going to Machu Picchu early, since the trains leave from Ollantaytambo or Urubamba anyway. Poroy, near Cusco, is out of service, so you are driving down to the valley regardless.
• You have had AMS before. Prior history is the strongest predictor there is.
• You are travelling with children, older relatives, or anyone with a reason to be cautious.
• You are heading into a trek and want the days to count.

It is not worth it if:

• You only have three or four nights in the region and would spend a fifth of them in transit.
• You have come up from Puno or Arequipa and are already adapted.
• Your accommodation is booked in Cusco and the point of the trip is the city.

Practicalities: the airport to Urubamba or Ollantaytambo is around 90 minutes. A private transfer runs roughly US$40 for a car and around US$70 for a van; a colectivo from the terminals in Cusco costs a few soles by comparison, plus a taxi to reach them. Note that the direct road climbs through Chinchero at about 3,760 m before it drops — higher than Cusco — which is fine for an hour in a car but not a place to linger on day one. And the valley is still 2,800 m. You can absolutely get AMS there. It simply shifts the odds in your favour. If you are still working out where to base yourself in Peru, this is a good reason to put the valley before the city rather than after it.

Arriving overland from Arequipa or Puno

The physiologically sensible way to reach Cusco is from below and slowly, which is what an overland southern-circuit route does almost by accident. Arequipa sits at about 2,335 m, which is a near-perfect staging altitude. From there the Colca Canyon route crosses Patapampa at over 4,900 m in a single morning — brutal, and by far the worst-designed ascent on the standard tourist circuit — before dropping to Chivay. Then Puno and Lake Titicaca at roughly 3,800 m, higher than Cusco. By the time you reach Cusco you are coming down, not up, and the city feels almost easy.

The trade-off is time. Two nights in Arequipa, two in Colca, two in Puno and the bus to Cusco is the better part of a week. The direct overnight bus from Arequipa to Cusco takes about ten hours and delivers you at 3,400 m having slept sitting up, which is physiologically gentler than the plane but hard on you in every other way. The Puno–Cusco day bus is around seven hours with stops, and is one of the more pleasant long journeys in the country. If you are still shaping the route, this is one of the few cases where the order of a Peru itinerary has real consequences for how you feel, and it is worth reading alongside the practicalities of moving between Peruvian cities.

Who is actually at risk

The honest answer is that susceptibility is largely genetic and there is no screening test for it. But some things do predict risk, and some widely believed things do not.

The strongest predictor is your own history. How you responded on a previous trip to a similar altitude at a similar rate of ascent is the most reliable guide available — and even that is not infallible. If you were ill in Quito or Lhasa or on a Colorado ski trip, plan for it here.

Fitness and youth are not protective. This bears repeating because it is the most dangerous misconception in Cusco. Training and physical fitness do not affect your risk. Children are as susceptible as adults; people over 50 are slightly less at risk, not more. Fit young travellers get AMS at the same rate as everyone else, and are conspicuously the group most likely to push through symptoms rather than admit to them. The Cusco cohort did find higher risk associated with obesity and with female sex, which cuts against the broader guidance that sex plays little role — the picture is not fully settled, and none of it should change what you do, which is to take symptoms seriously whoever you are.

Talk to a doctor first if you have: coronary artery disease, any significant chronic lung disease or existing low blood oxygen, obstructive sleep apnoea (severe OSA is a reason to avoid high-altitude travel without supplemental oxygen), sickle cell trait or disease, or poorly controlled diabetes — altitude illness can trigger ketoacidosis, and not all glucose meters read accurately up here.

Pregnancy: there are no studies or case reports of fetal harm from brief high-altitude travel, but the prudent advice is not to sleep above about 3,050 m. Cusco is above that. That does not automatically rule out the trip, but it does make it a conversation with your own doctor rather than something to decide from a blog, and it strengthens the case for basing yourself in the Sacred Valley.

Recent scuba diving: if you have been diving on the coast, respect the surface interval before you go to altitude. The Divers Alert Network guidance is at least 12 hours after a single no-decompression dive, 18 hours after multiple dives or multiple days of diving, and 24 hours after any dive requiring decompression stops. Flying to 3,400 m compounds this. Build the gap into the schedule.

One curiosity worth knowing if it applies to you: people who have had radial keratotomy can develop acute farsightedness at very high altitude. Newer laser procedures cause only minor disturbance, if any.

Cusco-specific practicalities nobody mentions

Take the first flight of the day. Cusco’s airport sits at 3,310 m in a valley, operates daylight-only with a visual approach, and has a single runway. Cloud and afternoon wind close it regularly, and the wet season from November to March is worse. Afternoon arrivals are cancelled far more often than morning ones, and when they go, they cascade. Booking the 06:00 also means that if it does fall over, you still have most of a day to be rebooked. This is not really an altitude point, but it is the single most common way people lose their carefully planned rest day.

Consider a pulse oximeter. They cost very little now and the Yellow Book suggests travellers may want one to gauge how acclimatisation is going. Set your expectations first: readings in the high 80s to low 90s are normal at 3,400 m and are not a reason to panic. The meaningful signal is a reading around ten points below the people standing next to you at the same altitude, particularly alongside breathlessness. Do not stare at the number. It is a tiebreaker, not a diagnosis.

Check what your insurance covers. Many policies cap altitude, often at 3,000 m or 4,000 m, which quietly excludes Rainbow Mountain and most of the trekking. Read the altitude clause and the evacuation clause before you buy, and factor any upgrade into your overall trip budget.

The air is dry as well as thin. You lose water just by breathing, the UV at 3,400 m is fierce even when it feels cold, and lips crack within a day. Lip balm with sun protection, real sunscreen and a hat matter more here than the temperature suggests. Layering advice for what to wear at Machu Picchu applies double in Cusco, where the swing between sun and shade is severe.

Ask your hotel what they actually have. Some Cusco hotels have oxygen-enriched rooms; many more keep cylinders and can call a doctor. It is a reasonable question to ask at booking, and a much better plan than searching for a clinic at 3am. This is worth building into your wider Peru trip preparation rather than leaving to chance.

How altitude shapes the rest of your Cusco trip

Once you know the elevations, a lot of common itinerary advice reveals itself as backwards. Going to Machu Picchu as a day trip from Cusco is exhausting for reasons of logistics, not altitude — you spend the day descending. Aguas Calientes at 2,040 m is the lowest place you will sleep in the region and a genuinely restorative overnight if you have been struggling.

Adding Huayna Picchu or Machu Picchu Mountain changes the calculation more than the citadel does, because those are steep climbs, even though the summits stay below Cusco’s elevation. They also cost more: circuits including either currently run S/211 for a foreign adult against S/163 for the standard entry, following the SERNANP conservation surcharge added on 1 May 2026. Check the official portal before booking, because these figures move.

Trekking is where altitude planning stops being optional. The classic Inca Trail crosses Dead Woman’s Pass at 4,215 m on day two, which is a serious ask from a body that flew in three days earlier. Salkantay goes higher still. Whichever of the multi-day treks in the Cusco region you choose, the acclimatisation days before the start are not padding sold to you by an operator — they are the part of the itinerary doing the work. And when you are deciding how many days to give the Machu Picchu leg, count the acclimatisation days as part of it rather than as time lost.

Season matters too, though less than people think. Altitude does not vary with the calendar, but the wet season brings the flight cancellations and the dry season brings colder nights and stronger sun. If you are still choosing months, the trade-offs in when to visit Peru are mostly about weather and crowds rather than how you will handle the elevation. And if your route also involves working out how to reach Machu Picchu, remember the train times are fixed and early — a 4am start on your second morning at 3,400 m is a bad plan whatever the schedule says.

Frequently asked questions

How high is Cusco exactly?

About 3,400 m, or 11,150 ft, measured around the Plaza de Armas. The airport is lower at 3,310 m and the upper neighbourhoods are higher. Different sources quote 3,350 m to 3,400 m and all of them are describing the same city.

Is Machu Picchu higher than Cusco?

No, and this is the fact most people get wrong. The Machu Picchu site is 2,430 m, almost 1,000 m below Cusco. Aguas Calientes, where you sleep, is lower again at about 2,040 m. If Cusco is bothering you, going to Machu Picchu will make you feel better rather than worse.

How many days do I need to acclimatise before Rainbow Mountain or the Inca Trail?

Two full days in Cusco before anything strenuous, and three before anything above about 4,500 m. Rainbow Mountain is 5,036 m — higher than any point on the Inca Trail, and only a few hundred metres below Everest base camp on the Nepal side. It is sold as a casual day trip. Treat it as a serious high-altitude day.

Does coca tea prevent altitude sickness?

No. A study of travellers arriving in Cusco found that drinking coca leaf tea to prevent AMS made no difference to who got it. It may relieve symptoms and it is culturally normal, so drink it if you like it — just do not treat it as protection, and remember it can trigger a positive drug test and is illegal to carry into most countries.

Should I take Diamox for Cusco?

If you are flying in from sea level with no acclimatisation days and no plan to sleep lower first, it is a reasonable thing to discuss with a travel clinic. Guidance advises a low threshold for prophylaxis precisely in this situation. The standard preventive dose is 125 mg every 12 hours starting the day before ascent and continuing two days at altitude. It is prescription-only, so sort it out before you fly.

Can I fly in and visit Machu Picchu the next day?

Physically, yes — you are going downhill. The problem is the 4am start and the long day, which is a lot to ask on your second morning at 3,400 m. If your schedule forces it, sleep in the Sacred Valley the night you arrive rather than in Cusco. You will be lower, closer to the train, and better rested.

How long does altitude sickness last in Cusco?

Mild AMS typically settles within 12 to 48 hours provided you do not go higher, and the whole thing usually develops and resolves over one to three days. If symptoms start after three days at the same altitude, or are getting worse rather than better, stop assuming it is altitude and get it looked at.

Is Cusco safe for children or older travellers?

Children are as susceptible as adults, not more, but they are worse at describing symptoms — watch for loss of appetite, unusual irritability and pallor in young children. Travellers over 50 are, on the guidance, at slightly lower risk than younger ones. Age is much less important than pre-existing heart and lung conditions, which are the thing to discuss with a doctor before booking.

What do I do if I feel genuinely bad in Cusco at night?

Tell reception. Hotels here deal with this constantly and can get a doctor to your room, usually within the hour, and bottled oxygen faster than that. Private clinics accustomed to treating travellers exist and several have hyperbaric chambers. If anyone is confused, cannot walk a straight line, or is breathless while sitting still, do not wait for morning and do not wait for a taxi to feel convenient.

The short version

Cusco will probably make you feel a bit rough for a day. Roughly two in five arrivals get symptoms that meet the definition of acute mountain sickness, almost all of it mild, almost all of it gone inside 48 hours. The way to stay in the “mild” column is unglamorous: fly in early, do nothing at all on your first afternoon, skip the alcohol, eat simply, sleep low in the Sacred Valley if the schedule allows, talk to a travel clinic about acetazolamide if it does not, and put the 5,000 m day trips at the end of the week rather than the beginning. Symptoms that get worse where you are mean you go down. Everything else is detail.