I believe that in some countries certain medications (e.g. antidepressants) are considered on a case-by-case basis. The rationale is that it's better to have the pilot on meds that keep him performing satisfactorily, rather than either taking the meds surreptitiously or having a breakdown. I've had the breakdown and, last time I checked, the meds which keep me happy and functioning prohibit even holding a PPL (although I can hold an NPPL; go figure)