I would wait until it comes up "naturally." When do you take your meds? If you have a conjunction between taking your meds and being with/going out with him (such that you have to take meds while you're with him or say, a sleep med before you get home from a date, etc.) then you can explain that med simply at that time? I myself would "joke" about the "difficult" meds but only after I'd been out and gotten to know the other person a bit to feel comfortable that when I said, "Excuse me, I have to take a little yellow pill now so I won't kill you later in a BP attack" (as opposed to PMS which guys seem to "get" :-) he would know it wasn't "that bad" and I could seque into a little about BP and how it affects me in a down-to-earth fashion he'd understand (no charts and graphs or big words :-)