What does “prn” mean?

At my recent doctor’s appointment, she said, “You’ll just take this prn.” (She pronounced each letter: P-R-N.)

“What does that mean?” I asked.

“It means you’re supposed to take it as needed.”

Suspecting it was a Latin abbreviation, since we were in a medical setting, I asked her what the full-length Latin word/phrase was. She was unsure. She said she was just used to seeing it in the abbreviated form.

So, dear friends, I did an investigation. It took me perhaps twenty seconds, but still, it was an investigation nonetheless.

Prn is short for the Latin phrase “pro re nata.” The doctor was correct in that it means “for an occasion that has arisen; as needed.

Now you know.