Which category of drugs requires the label "Rx only" to be present on the manufacturer's package?

The requirement for a drug to carry the "Rx only" label is indicative of its classification as a prescription medication. This label signifies that the drug can only be dispensed with a valid prescription from a licensed healthcare professional. In the context of the categories specified, Schedule III controlled drugs, which include substances that have potential for abuse but are deemed to have accepted medical use, fall under this requirement.

While Schedule I drugs are classified as having no accepted medical use and cannot be prescribed at all, and both Schedule II and Schedule IV drugs are also controlled substances with various levels of restrictions, the overarching requirement for a medication to have an "Rx only" label applies primarily to those that can be medically justified and are deemed necessary for treatment under professional supervision. Therefore, Schedule III drugs embody this category, as they necessitate a prescription but still allow for regulated use and distribution, as determined by healthcare professionals.