Traveling internationally with prescription medication requires carrying the original labeled bottle — and for controlled substances, many countries also require a doctor’s letter or certificate at the border.

Here’s the basic rule: always travel with your medication in its original labeled container — the one the pharmacy gave you with your name, the drug name, and the dosage printed on it. This applies to any prescription drug you’re bringing across an international border. According to the CDC and published research, travelers are typically advised to carry medications in their original labeled containers. That label is your proof that the medication is legitimately yours.

For stronger medications — things like painkillers, sleep aids, ADHD medications, anxiety medications, or anything considered a controlled substance — you’ll often need more than just the bottle. Many countries require a prescription or a medical certificate from your doctor, according to the CDC. Some medications that are completely legal in the U.S. are restricted or even banned in other countries, so this isn’t a situation where you can just assume you’re fine because a doctor prescribed it back home. Rules vary significantly by country, so always research your specific destination before you travel.

One practical detail: many countries only allow a 30-day supply of certain medications, per the CDC. If your trip is longer than that, talk to your doctor before you leave.

Research from PubMed Central specifically calls out psychotropics, narcotic analgesics, and certain substances like pseudoephedrine as categories where travelers need to pay extra attention to destination-country border rules. The short version: if your medication affects your brain, your mood, your pain levels, or your sleep, do your homework before you fly.

If you ever need to refill a prescription while you’re abroad, the CDC notes that drug names and formulations can differ from country to country, and counterfeit or substandard medications are common in many places — even in real pharmacies. Bringing your original labeled bottle and prescription gives a local pharmacist the best shot at matching you with the right equivalent medication. If you’re unsure which pharmacy to trust, the CDC recommends contacting the U.S. Embassy at your destination or consulting the International Society of Travel Medicine’s Global Travel Clinic Directory.

Bottom line: before any international trip, pull out every prescription medication you’re bringing, make sure it’s in its original pharmacy bottle, and ask your doctor for a signed letter or certificate — especially for any controlled substance. Research your destination country’s specific rules. Do this before you leave home, not at the airport.