Bringing Medication from Mexico to US: 90-Day Rule & CBP Laws

The bag and the mailbox are different imports

CBP’s traveler page and FDA’s personal-importation page cover the same drugs in two settings. Medicine in your luggage is examined, if at all, by a CBP officer at the port. Medicine in a parcel is screened at an International Mail Facility, with FDA responsible for the drug review. FDA’s manual says the agency spends more enforcement attention on commercial mail-order shipments than on products a person carries. That is an enforcement description, not a promise that a carried bottle will be waved through.

Same medicine, two legal settings. Mail detail lives on the shipping guide.
Question	Carried across the border	Mailed to a U.S. home
Who sees it first	A CBP officer at the land port or airport.	CBP at an International Mail Facility, then FDA if the parcel looks like a drug.
Non-controlled personal supply	Declare it. Original container, prescription or clinician letter, personal-use quantity.	Generally illegal to import. FDA may use discretion if its criteria are met. See the shipping guide.
Controlled substances	A narrow traveler exemption if the drug was lawfully dispensed, declared, and within the 50-unit limit for U.S. residents.	Illegal for a consumer to cause the drug to be mailed in. DEA registration is what the statute requires of an importer.
Where to read on	This page.	Online shipping guide

What FDA actually says

CBP tells U.S. citizens that, in most cases, it is illegal to obtain drugs outside the United States and import them for personal use. Foreign-made versions of U.S.-approved drugs have not been evaluated by FDA as those finished products, so FDA generally treats them as unapproved. CBP points travelers to FDA’s personal-importation policy for the limited circumstances in which staff may allow an entry.

On FDA’s page, a more permissive decision for a U.S. person is described when either of these is true:

The product is not for a serious condition and there is no known significant health risk.
The product treats a serious condition for which effective treatment may not be available in the United States, it is not being commercialized or promoted to U.S. residents, it does not pose an unreasonable risk, you affirm in writing that it is for your own use, and the amount is generally not more than a three-month supply. You also name the U.S. doctor responsible for the treatment, or show that the treatment started abroad.

Price is not on that list. A drug you can already fill at a U.S. pharmacy is a weak match for “effective treatment may not be available domestically.” FDA recommends legal U.S. sources for that reason.

Foreign nationals visiting the United States get plainer wording from FDA: a 90-day supply may be brought or shipped, and a longer stay may justify a later shipment, with a visa or passport copy, a doctor’s letter, and an English prescription. That is the visitor rule. It is not a standing import program for U.S. residents.

How to read the 90-day rule

CBP’s rule of thumb for travelers is to bring no more than a personal-use quantity, and it offers 90 days as that rule of thumb. FDA uses “generally not more than a three-month supply” inside the discretion policy. Both figures do the same job: they mark a personal amount and exclude a commercial quantity.

Count the supply against the prescription directions, not against a suitcase limit you prefer.
A 90-day box of a non-controlled drug can still be detained if another part of the policy fails.
Medicine for friends, resale, or a clinic is commercial, whatever the day count.
Controlled substances do not get this 90-day traveler rule. They have their own, smaller limit below.

Declaration at a land border

Declare the medication at primary inspection. Officers ask what you are bringing back. Answer with the truth: prescription medicine for your own use. Describing it as vitamins, a gift, or “nothing” is a false statement.

Carry a WHTI-compliant document for re-entry, in practice a passport book or passport card. Check CBP’s current document list before you go.
Keep the medicine in the original container. Bring the prescription or a clinician letter in English.
Bring a personal amount. For non-controlled medicine, 90 days is the working ceiling CBP and FDA describe.
Carry medicine that was dispensed to you. A bottle with someone else’s name is not your personal supply.
If you are sent to secondary inspection, show the documents and let the officer examine the boxes.

Town-by-town notes for Los Algodones, Tijuana, and Nogales, including where people park and walk, are on the border-town page.

Controlled substances when you are physically crossing

DEA regulation 21 CFR § 1301.26 lets a person enter or leave the United States with a Schedule II, III, IV, or V substance in their possession, despite the import offenses in the statute, only if all of the conditions are met. The substance has to have been lawfully obtained for that person’s medical use. It has to be in the original container in which it was dispensed. The person has to declare it to a customs officer, including that it is for personal use, and has to be able to identify it from the label or by the pharmacy, prescriber, and prescription number.

For a United States resident, there is a further cap: no more than 50 dosage units combined of all such controlled substances obtained abroad. The 50-unit cap does not apply to controlled substances that were lawfully obtained in the United States on a prescription from a DEA registrant and are being brought back. “Lawfully obtained” matters. A controlled drug sold in Mexico without the prescription Mexican law requires was not lawfully dispensed, and the exemption does not cover it.

Fifty units is a ceiling for drugs that already qualify. It is not a shopping allowance, it is not 50 units per drug, and it is not a suggestion to carry benzodiazepines, opioids, tramadol, stimulants, or scheduled sleep medicines as a routine border purchase. Declare anything you do carry. An undeclared controlled substance fails the regulation on its face.

Medicines that are restricted or refused

Schedule II–V drugs outside the traveler exemption, and any consumer mail order of those drugs.
Counterfeit, unlabeled, or repackaged loose tablets.
Products promoted as unorthodox cures for conditions such as cancer, HIV, arthritis, or multiple sclerosis. FDA and CBP both flag health fraud.
Quantities that look commercial, including medicine for other people.
Products FDA has placed on an import alert for previous violations.
Cold-chain drugs that were not kept at the labeled temperature. Those are a safety failure even when the paperwork is tidy. The shipping guide explains why mail is a bad tool for them.

Antibiotics have required a prescription in Mexico since 2010. They remain prescription drugs for any personal-importation claim, and a new infection belongs with a clinician rather than a border special.

If an officer detains the medicine

At the port, detention of something in your bag is usually immediate and verbal: the officer holds the product, asks questions, and may refuse entry of that item while admitting you. Cooperate, show the prescription, and do not argue a controlled-substance purchase into the 90-day policy. The 90-day policy is the wrong rule for that product.

A mailed shipment produces paper instead. FDA issues a Notice of FDA Action. CBP may issue a seizure notice when the goods are prohibited. Deadlines and options are printed on the form you received. The response steps, and the reason a reship is not an answer to the notice, are on the shipping page.

Sources

Follow the agency page if it has been updated since this review.