My own two cents and experience
part of my osteo-arthritis management is up to 1000mg of Paracetamol (acetamenophen) per day, as needed. I cleared with my GP that this poses no danger to, after, before, or around Scuba Diving.
I also take 60mg Duloxetine (Cymbalta) for my Fibromyalgia treatment, and same here: No adverse advice to scuba diving
So I would assume, the normal headache treatment dose of an occasional 500mg of Tylenol/Panadol/Paracetamol/Acetamenophen should not pose any risk, unless you are inherently allergic to the drug. But that's then nothing to do with diving