Prescription-Only Status (Rx-Only)

The prescription and over-the-counter divide was created by the Durham-Humphrey Amendment of 1951. A drug is prescription-only if, because of toxicity, its method of use, or the collateral measures necessary to its use, it is not safe except under practitioner supervision. Such products bear the statement Rx only, successor to the caution legend that gave the term legend drug. The classification belongs to the product as approved, not to the molecule: the same ingredient can be prescription at one strength and over-the-counter at another.

Movement between the categories is formal: a switch requires either an application showing the product can be used safely by a consumer on its labelling alone, or action under the over-the-counter monograph system, restructured in 2020 into an administrative order process. Recent switches, including naloxone nasal spray and a daily oral contraceptive, applied those criteria to products previously thought to need supervision. Classifications are revised, so a current status should be read from the regulator's register.

For peptides the classification is close to universal, following from the dosage form as much as the pharmacology: parenteral products needing monitoring are not candidates for self-selection. A prescription-only product reaching a patient with no prescriber, pharmacy record or lot number has therefore left the regulated route somewhere.

The error to name precisely is treating research use only labelling as a third category that sidesteps the prescription requirement. It is not a classification at all, and a peptide sold that way for human use remains an unapproved and misbranded drug. The related confusion calls an unapproved substance prescription-only, when something with no approval is neither: classification is assigned at approval, and there was none.