What it actually feels like
Mexico City sits two thousand two hundred and forty metres above sea level, higher than any European capital and considerably higher than Denver, which is the reference people usually reach for. At that altitude there is roughly twenty-three per cent less oxygen available in each breath than at sea level. It is not a dramatic figure and the overwhelming majority of visitors have no serious trouble, but the body registers it, and registers it in ways almost nobody attributes to altitude.
The typical experience is not the mountain sickness of documentaries, with nausea and severe dizziness. It is an odd tiredness that arrives mid-afternoon for no reason, a dull headache by the end of the day, sleep that does not restore you for the first two nights, a dry nose and throat on waking, and running out of breath on three flights of stairs even if you run half marathons at home. Add a long-haul flight and a time change and the result is a first day well below expectations.
The first forty-eight hours
The adjustment takes twenty-four to forty-eight hours in most people, and all you can do is go with it rather than fight it. Drinking far more water than usual, eating lightly at night, going fairly easy on alcohol and scheduling absolutely nothing demanding on the first day resolves ninety per cent of cases. Two thousand two hundred metres needs no medication and no special preparation; it needs two slow days and an acceptance that the trip really starts on the third.
The commonest planning error by a wide margin is booking the hardest excursion for the morning after landing. Teotihuacán, with three kilometres of avenue in full sun and the steep platform staircases, is exactly what you should not attempt on day two with jet lag still on you and the body unadjusted. Moving it to day three or four costs absolutely nothing, disturbs nothing else in the itinerary, and completely changes how that visit is remembered.
The other half of the problem: the air
Altitude does not travel alone in this city, and the whole picture is worth telling. Mexico City sits in a valley closed by mountains and suffers thermal inversions that trap pollution at street level, particularly during the dry season. March to May is when most poor-air-quality episodes are declared, and on the worst days the authorities activate driving restrictions and advise reducing outdoor physical activity. It is not the daily norm, but it happens several times a year and is worth knowing in advance.
For a healthy visitor the practical effect is minor and perfectly manageable: the odd day with a scratchy throat, dry eyes and a hazy view across the valley from any rooftop. For anyone with asthma or a chronic respiratory condition it is a genuine factor in choosing the month. The rainy season, June to September, has noticeably cleaner air because the daily storm washes the atmosphere; the price is that it rains most afternoons.
Who should check before travelling
For the great majority of travellers, two thousand two hundred metres calls for no medical precaution and no preparation at all. But there are specific profiles where a short conversation with your own doctor before buying the ticket is worthwhile, and that conversation is quick and cheap compared with discovering the problem six thousand kilometres from home. This page is not medical advice and under no circumstances replaces that consultation; it only flags the cases where asking first makes sense.
It is also worth knowing that the typical central-Mexico trip does not stop at two thousand two hundred metres, far from it. Toluca is at two thousand six hundred and sixty, the road pass towards Puebla crosses above three thousand, and anyone deciding to climb the Nevado de Toluca or the Ajusco on a day trip goes past four thousand metres. Those particular excursions are an entirely different matter and deserve their own question, with the name and the altitude on the table.
The altitudes on the standard route
Almost every central-Mexico itinerary moves between one thousand seven hundred and two thousand six hundred metres, and the order in which you travel them matters considerably more than it looks. Starting in the capital, continuing in Puebla and finishing in Querétaro or Guanajuato is a gentle, progressive descent the body appreciates; the reverse, with maximum altitude at the end and fifteen accumulated days of travel behind you, shows up in the legs and in the sleeping.
It also helps to know which of the famous visits is genuinely high and which is not. Teotihuacán is slightly lower than the city itself, and the effort there is sun, dust and staircases rather than thin air. Puebla and Cholula sit just below the capital. The only serious climb on a classic highland itinerary is the mountain pass between Mexico City and Puebla, and you cross it comfortably seated on an air-conditioned bus.
The mistakes people keep making
Almost no visitor has a medical problem with the capital's altitude, and that is worth saying first so as not to alarm anybody. What a great many people do have is a bad first day, and almost always for the same four reasons: landing at night after twelve hours in the air, going out for a heavy, late dinner, drinking as they would at home, and having an excursion booked for seven the next morning with hotel pick-up.
There is a fifth, less obvious and very common error: misreading the signals. People blame the tiredness on the flight, the headache on cabin dehydration and the poor sleep on jet lag, and push on as though nothing were happening. Recognising that it is the altitude changes the decision: instead of having a coffee and heading out, you rest for two hours and recover the whole afternoon. The difference between those two choices shows for the rest of the week.
What people always ask
Six concrete questions about the capital's altitude, answered without drama and without playing it down, which are the two usual extremes online. They run from the most practical to the most specific, and the last compares the capital with the two other destinations that usually share the same itinerary, because the contrast helps separate what is altitude from what is simply a lot of travelling.
One question deserves an answer even though it is almost never asked: how long the body takes to unwind on getting home. The answer is very little, and generally pleasantly. Dropping to sea level after a week at two thousand two hundred metres produces, for a few days, the sensation of extra energy that athletes know well. It is the one side effect of the trip that nobody complains about, and it lasts two or three weeks.