Diamox (acetazolamide) is not available over the counter in the United States. It is a prescription-only medication, meaning you need a doctor’s order to obtain it from a pharmacy. This applies to all forms of the drug, whether you’re seeking it for altitude sickness prevention, glaucoma, or any other use.
Why Diamox Requires a Prescription
Acetazolamide is a carbonic anhydrase inhibitor, a class of drug that changes the chemistry of your blood. It works by forcing your kidneys to excrete bicarbonate, which makes your blood slightly more acidic. Your body interprets this shift as a signal that carbon dioxide levels are too high, so it responds by making you breathe faster and deeper. The result is more oxygen in your bloodstream, which is why the drug works so well for altitude sickness prevention.
That same mechanism is also why it’s not sold freely off the shelf. The drug alters your blood pH, acts as a diuretic, and can interact with other medications. Dosing needs to be tailored: the CDC recommends 125 mg twice daily for most adults, but 250 mg twice daily for people over 100 kg. People with certain kidney conditions or electrolyte imbalances need medical screening before taking it.
How to Get a Prescription
Getting a Diamox prescription is usually straightforward if you’re planning a high-altitude trip. Most primary care doctors and travel medicine clinics will write one after a brief conversation about your travel plans and medical history. Telehealth visits are another common route, and many online services can issue a prescription quickly if altitude sickness prevention is your goal. You’ll typically start the medication the day before ascending and continue it for the first two days at altitude, or longer if you keep going higher.
One concern that comes up frequently is sulfa allergies. Acetazolamide contains a sulfonamide functional group, which leads many patients and even some pharmacists to flag it. However, the cross-reactivity risk is very low. Unlike sulfonamide antibiotics, acetazolamide lacks the chemical structures (specifically the N1 ring and N4 amine group) responsible for allergic reactions. Research published through NCBI concluded that a sulfonamide allergy should not be considered a contraindication to acetazolamide. Still, mention any drug allergies when you speak with your doctor.
Common Side Effects
Acetazolamide has a well-documented side effect profile, and tingling in the hands, feet, and face is by far the most common. A large meta-analysis found that about 51% of people taking the drug experienced this tingling sensation, making it more of an expected effect than a rare one. It’s harmless but can be uncomfortable enough to catch you off guard if you’re not expecting it.
Other side effects include increased urination (around 13.5% of users), fatigue, and an altered taste, particularly a metallic or flat taste with carbonated drinks. The number needed to harm for taste changes was 18, meaning roughly 1 in 18 people will notice it compared to placebo. These effects generally resolve quickly after stopping the medication.
Buying Diamox Abroad
If you’re traveling internationally, prescription rules vary by country. In Peru, for example, acetazolamide is widely available over the counter at local pharmacies in cities like Cusco. Travelers heading to high-altitude destinations in South America often purchase it on arrival without a prescription. However, quality control and dosage accuracy can vary at pharmacies in some countries, so obtaining a prescription before you leave home gives you more control over what you’re taking.
Over-the-Counter Alternatives for Altitude
Several supplements are marketed for altitude sickness prevention, but the evidence behind them is weak compared to acetazolamide. Ginkgo biloba is the most commonly discussed alternative. A Cochrane review of seven studies involving 523 participants found no clear benefit over placebo for preventing acute mountain sickness. When ginkgo was compared head-to-head with acetazolamide across four studies, the results were inconsistent and no conclusions could be drawn.
Other supplements fare no better. Rhodiola crenulata showed no effect in a trial of 125 participants. Antioxidant supplements, iron, and hormonal agents all produced results that were statistically uncertain and based on small, low-quality studies. None of these have anywhere near the evidence base supporting acetazolamide.
Ibuprofen has shown some promise in studies for altitude headache prevention and is genuinely available over the counter, but it works through a completely different mechanism and isn’t a substitute for how acetazolamide helps your body acclimatize. For people who can’t take acetazolamide, ibuprofen is sometimes discussed as a partial option, but this is a conversation worth having with a doctor rather than a self-treatment decision.