Kilimanjaro Altitude Sickness: What a Two-Time Summiter (and Doctor) Wants You to Know Before You Climb
Climbing Kilimanjaro is one of the few adventures where you can be in great shape and still get taken down by the mountain — or be completely out of shape and still summit. I know this firsthand: I hiked Kilimanjaro as a 25-year-old medical student, inspired by Michael Crichton's memoir Travels, where he writes about trekking it himself. Crichton did the climb while smoking about half a pack a day. If he could get up that mountain, I figured, so could I. I went back and summited again years later as a 41 year-old. Both climbs taught me the same lesson. That's the first thing I want you to walk away from this post knowing: fitness is not a measure of how you'll handle altitude. Altitude sickness doesn't care about your VO2 max. It cares about how fast you ascend and how your individual physiology responds to thinning air.
Here's what actually matters, from a physician who's done the climb and now runs a pre-travel health consult practice built around exactly this kind of trip.
Hydrate aggressively — and not just with water
At altitude, your body loses fluid faster than you realize — through faster breathing, drier air, and increased urination as your kidneys work to help you acclimatize. Plain water alone isn't enough. You need to hydrate aggressively with a mix of water and something with glucose and electrolytes. I'm a fan of Liquid IV powder packs for this — easy to pack, easy to mix into a bottle at camp.
On water safety: your porters will bring your bottles full of boiling hot water at camp, which is generally safe on its own. I still brought chlorine tabs as backup, just to be safe, and I'd recommend the same — so here's the workflow: once your porters hand you your bottles of boiling water, drop in a chlorine tab, then throw the sealed bottle in the bottom of your sleeping bag.
Pro tip: that's a two-for-one move. You get safely treated water for the next day, and a hot bottle at your feet keeps you warm and cozy all night. You'll sleep better at altitude, which is a bigger deal than it sounds when you're shivering at base camp at 15,000 feet.
Acetazolamide, and starting it early
Acetazolamide (Diamox) is definitely advised for Kilimanjaro. Start it the day before your hike begins, not the day you leave. It can cause tingling in your fingertips — that's a known, expected side effect and not something to worry about. Lower doses can actually work fine in most people; something we can discuss.
The single biggest lever you have for avoiding altitude sickness, though, isn't a pill — it's pace. Pole pole (Swahili for "slowly, slowly") is the mantra for a reason. Ascend slowly and trust your body. The good news is you don't have to engineer this yourself: a slow ascent is usually already baked into any reputable trekking company's itinerary. Trust the your guide on this one.
GI prep: nausea, diarrhea, and what each one means
Pack dissolvable ondansetron in case you get nauseated. But treat nausea as information, not just a symptom to medicate through — it's usually a sign to slow down or descend, not just push through with a pill.
You'll also want azithromycin and loperamide on hand in case of traveler's diarrhea. Trust me: dealing with diarrhea in a bucket or a porters' potty at 15,000 feet is not a fun experience, and having the right meds with you turns a miserable night — and potentially trip-theatener — into a manageable one. (See my next post for guidance on exactly when it's time to start the azithromycin.)
What about your malaria pills?
This one comes up a lot, and the honest answer is a little more nuanced than most packing lists let on. Malaria-carrying mosquitoes generally aren't found much above roughly 1,800 meters (about 5,900–6,000 feet), so once you're high on the mountain itself, your actual transmission risk drops close to zero. Technically, you could pause your antimalarial above that altitude and resume it once you descend below that level.
In practice, I don't recommend it. Almost every Kilimanjaro itinerary includes real time below that altitude threshold — Moshi or Arusha before and after the climb, plus any safari or Zanzibar add-on — which is exactly where your actual malaria risk is highest. Stopping and restarting just means one more thing to remember on a trip where you're already juggling gear, guides, and a summit push. I'd rather you just stay on your daily dose the whole trip. It only costs you a few days of medication you technically didn't need, versus the real risk of forgetting to restart once you're back below altitude.
Gear that actually matters
Beyond the meds, a few things make the biggest difference: hiking boots with good ankle support, and plenty of layers for the cold. Temperature swings on Kilimanjaro are extreme — you'll be sweating through an uphill climb through a rainforest zone on Day 1 and layered up against sub-freezing temps by summit night. Don't skip SPF 50+ sunscreen, either — you're closer to the sun at altitude and the UV exposure is brutal, even when it's freezing.
My favorite parts of the trek
If you're wondering whether the misery is worth it — it is, and not just for the summit photo.
Hiking-wise: Barranco Wall. It's the scramble everyone talks about, and it earns the hype.
Mentally: Stella Point. That's the moment you know you're almost there!
Socially: the porters. After dark, there's a subtle rumble of them chatting and laughing in lit-up tents — one of my favorite, most underrated parts of the whole experience.
A word on cutting it close (don't do this, but here's what happened)
On our 2023 climb, our flight into JRO got delayed. We landed around 9:00 AM, went straight to the hotel to change and re-pack our bags, and were at the trailhead by 1:00 PM. Same day. Not recommended — but we figured if we were going to be tired either way, we might as well start hiking. Build in buffer time if you can. We didn't have the luxury, and it worked out, but don't plan your trip assuming it will. (We’d also just come from living at about 5,000 ft above sea level, so we were pre-acclimatized to a degree.)
After the summit: where to recover
Once you're off the mountain, give yourself real R&R. Zanzibar is the classic choice and it's great. The night market in Stone Town is a unique casual dinner spot and the beaches don’t disappoint. (Have a dhow to celebrate!) Diani Beach, across the border in Kenya, is also a lovely option if you want something a little different.
Planning a Kilimanjaro climb and want your prep dialed in — meds, timing, and what's actually worth worrying about? Book a pre-travel consult and we'll build your plan together.
Safari njema!
