Importation of any prescription drug (not necessarily a controlled substance) violates 21 USC, Section 301(aa), unless the following conditions are met (as listed in Section 804):
1. The drug is imported from Canada, from a seller registered with the Secretary (i.e. with FDA);
2. The drug is imported from a licensed pharmacy for personal use by an individual, not for resale, in quantities that do not exceed a 90-day supply;
3. The drug is accompanied by a copy of a valid prescription;
4. The drug is a prescription drug approved by the Secretary;
5. The drug is in the form of a final finished dosage that was manufactured in an establishment registered under section 510; and
6. The drug is imported under such other conditions as the Secretary determines to be necessary to ensure public safety.
# The law further specifies that enforcement should be focused on cases in which the importation by an individual poses a significant threat to public health, and discretion should be exercised to permit individuals to make such importations in circumstances in which the prescription drug or device imported does not appear to present an unreasonable risk to the individual.
# According to Department of Homeland Security Appropriations Act, Section 535, Customs and Border Patrol are not allowed to prevent people from importing FDA-approved prescription drugs. Although originally the law was worded to cover all prescription drugs, countries of origin, and methods of delivery, its final edition specifies that it only applies to importation from Canada, and to "...individuals transporting on their person a personal-use quantity of the prescription drug, not to exceed a 90-day supply". Controlled substances are also explicitly excluded. Therefore, it does not disallow Customs to screen and intercept drugs sent by mail.
# It is also technically illegal to import "non-approved" drugs (21 USC sections 331(d) and 355(a)); however, FDA policies suggest that, under certain circumstances, the patients may be allowed to keep these drugs.
# Individual U.S. states may implement their own laws regulating importation, possession, and trafficking in prescription drugs and/or controlled substances. In contrast, for years the states of Nevada, Minnesota, Illinois and Wisconsin have run official state programs to help their residents order lower-cost drugs from abroad to save money.