PRN means a medication is taken "as needed" rather than on a fixed schedule. It comes from the Latin "pro re nata," meaning "as the situation arises." A PRN medication is one you take only when a specific need occurs, such as pain, nausea or anxiety, rather than at set times every day.

This is general information, not medical advice. Always follow your prescriber's instructions for any PRN medication.

How is PRN dosing different from scheduled dosing?

A scheduled medication is taken at fixed times regardless of how you feel, to keep a steady level in your body. A PRN medication is taken in response to a symptom, within limits your prescriber sets, such as a minimum gap between doses and a maximum number in 24 hours.

Because PRN medications have no fixed schedule, they are normally excluded from an adherence rate, which only measures scheduled doses.

What are the limits on PRN medications?

PRN does not mean unlimited. Two limits usually apply:

  • A minimum gap between doses, for example "no more than once every 4 hours."
  • A daily cap, for example "no more than 4 doses in 24 hours."

Staying within both is how PRN medications stay safe. Tracking when you last took a dose, and how many you have had today, is the practical challenge with as-needed medication, which is why a tracker that shows your countdown and your remaining daily allowance helps.

Common examples of PRN medications

PRN is common for things like pain relief, anti-nausea medication, rescue inhalers and some anxiety medications. The specific rules vary widely by medication, so always follow the directions on the label and ask your pharmacist if you are unsure.

Frequently asked questions

What does PRN stand for?

PRN stands for the Latin "pro re nata," meaning "as the situation arises," and is used to mean a medication taken as needed rather than on a fixed schedule.

Does PRN mean I can take it whenever I want?

No. PRN medications usually have a minimum gap between doses and a maximum number allowed in 24 hours. You take them as needed within those limits, which your prescriber and the label define.

Are PRN medications counted in my adherence rate?

No. Because they have no fixed schedule, PRN medications are normally excluded from an adherence rate, which measures only scheduled doses.

Cadence is a free medication reminder app for iPhone that tracks as-needed medications with optional dose spacing and a rolling 24-hour cap. It is not medical software and does not provide medical advice. Cadence Pro is $9.99 as a one-time purchase.