What happens when both PRN and ad lib are indicated on a prescription?

When both PRN (pro re nata, meaning "as needed") and ad lib (from the Latin "ad libitum," meaning "at one's pleasure") are indicated on a prescription, it generally signifies that the medication may be taken at the patient's discretion, depending on their needs or preferences.

In this context, while it might seem that refills could be allowed because of the nature of PRN and ad lib, regulatory guidelines typically dictate that if a prescription indicates usage on an as-needed basis, it often limits the ability for refills. This is because the need for the medication may vary significantly from patient to patient, and the prescriber may want to monitor the patient's condition carefully before approving further supplies of the medication.

Thus, the dose and frequency being dictated as PRN and ad lib can lead to a situation where refills being permitted is not applicable, ensuring that there is close oversight of how the medication is utilized. This helps prevent misuse or overages which could occur if refills were allowed under such broad directives. Therefore, no refills are typically allowed under these conditions.