Rule of thumb: When you go abroad, take the medicines you will need, no more, no less. Narcotics and certain other drugs with a high potential for abuse - Rohypnol, GHB and Fen-Phen, to name a few - may not be brought into the United States, and there are severe penalties for trying to do so.

When returning from Mexico to the U.S. in 2026, strict FDA and CBP regulations govern what medications can legally cross the border. You generally cannot bring back any medication that is not approved by the FDA, even if it is legal in Mexico. This includes "unorthodox cures" for cancer or AIDS and medications like Rohypnol (the "date rape" drug), GHB, or Fen-Phen. You are also prohibited from bringing back narcotics like medical marijuana, even with a Mexican prescription. Most notably, you cannot import Mexican versions of U.S. drugs (like cheap antibiotics or steroids) for personal use if they haven't been FDA-vetted. If you are a U.S. resident carrying a controlled substance (like certain stimulants or tranquilizers) obtained in Mexico without a U.S.-licensed prescription, you are typically limited to 50 dosage units. To avoid seizure or severe penalties, all legal medications must be declared to CBP officers, kept in their original containers with the prescription printed on them, and be in quantities consistent with personal use (usually a 90-day supply maximum). Only medications that can be legally prescribed in the United States are eligible for personal importation.