What is one requirement for the mailing of controlled substances?

The requirement stating that the mailer or addressee must be exempt from DEA registration highlights important regulatory considerations in the shipping of controlled substances. For controlled substances to be mailed legally, either the entity sending or receiving the package must comply with DEA regulations which typically means they must be registered. This means that either the pharmacy (or other authorized sender) must have a valid DEA registration to send controlled substances, or the patient receiving the medication must also be legally permitted to handle such substances, such as holding a valid prescription.

This requirement is crucial for maintaining the security and tracking of controlled substances to prevent abuse and diversion. Regarding the other options, while pharmacies generally have the authority to mail controlled substances, it is not limited only to them, and the patient or addressee can also be involved without any specific load limit or registration exemptions. Thus, the rationale behind this specific choice aligns closely with maintaining the regulatory framework upheld by the DEA concerning the shipment of controlled substances.