Altitude Sickness in Colorado: How to Prevent It & What Works

Colorado is one of the highest-elevation states in the U.S. Denver sits at 5,280 feet, Vail at 8,150, Leadville at 10,152, and trailheads above 11,000 feet are routine. If you live near sea level and fly in for a weekend, your body has roughly 48 hours to figure out how to function on 30-40% less oxygen than it's used to. For most people that goes fine. For some — and the difference is unpredictable from one trip to the next — it goes badly. Altitude sickness sends visitors to emergency rooms in Summit County and Eagle County every weekend during ski season.

The good news: altitude sickness is almost entirely preventable, and the few cases that develop are almost always treatable if you catch them early. Here's how to do both.

What Altitude Sickness Actually Is

Altitude sickness — also called acute mountain sickness (AMS) — is what happens when your body hasn't yet adjusted to lower atmospheric pressure at high elevation. The air at 12,000 feet contains the same 21% oxygen as the air at sea level, but the lower pressure means each breath delivers fewer oxygen molecules to your bloodstream. Your body responds by breathing faster, producing more red blood cells, and shifting fluid balance. The adjustment process is called acclimatization, and it takes 1-3 days for the major changes and weeks for the full adaptation.

When the symptoms exceed what acclimatization can keep up with, you get AMS. There are three severity levels:

1. Acute Mountain Sickness (AMS). Headache, nausea, fatigue, sleeplessness. Roughly 25% of unacclimatized travelers above 8,000 feet get some form of it. Annoying but not dangerous if you stop ascending.

2. High Altitude Pulmonary Edema (HAPE). Fluid accumulates in the lungs. Symptoms include extreme shortness of breath at rest, dry persistent cough, gurgling sounds when breathing, chest tightness. Onset typically 2-4 days after arrival. This is a medical emergency.

3. High Altitude Cerebral Edema (HACE). Fluid in the brain. Symptoms include severe headache that doesn't respond to medication, confusion, loss of coordination (can't walk a straight line), hallucinations. Also a medical emergency.

HAPE and HACE are uncommon for typical Colorado visitors at typical ski-town elevations (8,000-10,500 feet), but they happen often enough that mountain town ERs are practiced at treating both. The risk goes up sharply above 12,000 feet — which is where many 14er trailheads sit.

Symptoms — What to Watch For

Most altitude sickness shows up within 12-24 hours of arrival at elevation. The classic early warning signs:

Headache. Almost universal. Usually frontal, dull, and worse with exertion or lying flat. If ibuprofen doesn't touch it, that's a flag.

Nausea and loss of appetite. You won't want to eat. Eat anyway — your body needs fuel to acclimatize.

Fatigue and sleeplessness. You'll feel tired but won't sleep well. People often describe waking up gasping for air at 2 AM. This is normal early AMS and usually resolves by night 2 or 3.

Lightheadedness. Mild dizziness when standing. Worse if you've been drinking alcohol or are dehydrated.

These are uncomfortable but not dangerous. The line you need to know:

Stop ascending if symptoms are getting worse. Descend if symptoms are severe or if you see HAPE/HACE signs. That's the entire decision tree. Most altitude trouble comes from people pushing through symptoms instead of pausing or going down.

Prevention — What Actually Works

Ascend gradually

The single most effective prevention is to give your body time. The general rule above 8,000 feet: above your sleeping elevation, gain no more than 1,000-1,500 feet per night, and take a rest day every 3,000-4,000 feet of cumulative elevation gain.

For typical Colorado visitors: spend at least one night in Denver (5,280 ft) before heading to Vail (8,150 ft) or Aspen (7,908 ft). Spend a night at 8,000-9,000 feet before camping at 11,000 feet. Don't fly into Denver and drive straight to a 12,000-foot trailhead the same day — you're stacking the deck against yourself.

Hydrate aggressively

Dry air at altitude pulls water out of you faster than you'll realize. Most people need 3-4 liters of water per day at elevation, not the usual 2. Symptoms of dehydration overlap heavily with symptoms of AMS, which means dehydration both causes and masks the real problem.

A 3-liter hydration reservoir is the simplest fix on the trail. At camp, an insulated water bottle keeps water from freezing overnight and lets you drink first thing in the morning, when hydration matters most.

Skip the alcohol the first 48 hours

This one's not negotiable. Alcohol at altitude hits 2-3x harder, dehydrates you, depresses your respiratory drive (which is exactly what you don't want), and reliably triggers AMS in people who'd otherwise be fine. The mountain town tradition of "drink your way through it" sends a few hundred people to Colorado ERs every winter. Wait until night 3.

Eat carbs

At altitude your body burns through glycogen faster, and a high-carb diet has been shown in multiple studies to reduce AMS severity. The mountain food clichés exist for a reason: pancakes, oatmeal, pasta, rice. Eat them. The traditional alpine breakfast of eggs and bacon is fine but pair it with toast or potatoes.

Sleep low

If your itinerary is flexible: drive up to high elevation for hiking or sightseeing during the day, but sleep at a lower elevation when you can. "Climb high, sleep low" is the mountaineer's mantra and it works.

Medications That Help

Ibuprofen

The most common altitude headache responds well to standard ibuprofen (400-600 mg every 6 hours). One 2012 randomized trial showed prophylactic ibuprofen taken 6 hours before ascent reduced AMS incidence by about 25%. Cheap, no prescription, no real side effects at normal doses.

Acetazolamide (Diamox)

If you've gotten AMS before, or if you can't avoid a fast ascent, ask your doctor about acetazolamide. It speeds up acclimatization by slightly acidifying your blood, which stimulates breathing. Standard preventive dose is 125 mg twice daily, starting the day before ascent and continuing for 2-3 days at altitude. Side effects include tingling in the hands and feet and altered taste (carbonated drinks taste flat). Not a casual prescription — talk to your doctor first.

Aspirin

Aspirin works similarly to ibuprofen for the headache and has the bonus of mild blood-thinning effects. Some studies suggest a slight benefit over ibuprofen for altitude headache specifically, though results are mixed.

Things that don't work (despite the marketing)

Several products are sold specifically for altitude sickness with little to no clinical evidence behind them. Oxygen cans ($15-25) give you 60 seconds of supplemental O2 — pleasant, useful in the moment, but they don't acclimatize you. Coca leaf products are a long tradition in the Andes but evidence for them in Colorado-style altitude exposure is thin. Most "altitude pills" sold on Amazon contain combinations of vitamins and herbs (ginkgo, rhodiola, vitamin C) — the evidence on ginkgo is weakly positive, the rest are mostly placebo.

If you want something low-risk and over-the-counter, ginkgo biloba has some positive trial data at 120 mg twice daily started 5 days before ascent. Iron supplements help women with low ferritin levels acclimatize better — worth checking your iron status if you struggle at altitude.