When must a physician or practitioner sign a prescription for a controlled substance?

A physician or practitioner is required to sign a prescription for a controlled substance at the time of issuance to ensure that the prescription is valid and legally compliant. This signature serves as a confirmation that the prescriber has evaluated the patient, determined that the medication is necessary, and officially authorized its dispensing.

Signing at this point is crucial because it establishes the date and intent behind the prescription, thus protecting both the patient and the pharmacy. It also helps in maintaining the integrity of the prescription process for controlled substances, which are subject to strict regulations to prevent misuse and ensure safe prescribing practices.

The other options suggest signing at different times or under different circumstances, which do not align with the legal requirements for issuing prescriptions for controlled substances. For example, signing after the patient receives the medication or at the end of treatment does not ensure that the prescription was issued with proper oversight or control, potentially compromising patient safety and regulatory compliance.