An example of an exception is doing a very occasional prn with a medication to reduce extreme anxiety. For example, I'm prescribed 250mg/day Seroquel. A couple of times over the past three months I've taken an extra 50mg in the morning because I was feeling especially anxious & not able to get control of the anxiety.

I've been taking p-meds for 30+ years. It isn't unusual for a p-doc to ask me what I think will work best for me, then prescribe whatever I say. I don't have a history of abusing meds, street drugs, or alcohol...the occasional prn isn't going to do any harm for me.