There is also the very grey area of prescription medicine. If you are on something as simple as pain killers (e.g. co-codamol) it could be a difficult thing to justify you were/are fit to drive. And don’t rely on a GP to back you up in court as they will not be able to say at a particular point in time, if you were fit to drive.
As with alcohol and recreational drugs, different people are affected differently. I have pain relief I can only take at night as I know there’s no way I’d be fit to drive within 4 hours of taking them. Fortunately the rest doesn’t impede my driving. However, I know my wife taking the same drugs would be barely able to find the car.
It’s hard to gauge as some effects are difficult to tell yourself but if there’s any way your reactions are slowed, then there’s every chance that, should an accident happen (even if you’re not at fault) you could be declared unfit to drive.
I'm Autistic, if I say something you find offensive, please let me know, I can guarantee it was unintentional.
I'll try to give my honest opinion but am always open to learning.
Mark