I'm ADD Inattentive and using Venlafaxine. I was diagnosed within this past year and so I haven't been using medication for very long.
I find that caffeine typically has no effect on me whatsoever- good or bad. I can sleep immediately after without any problems. Occasionally I have good focus after caffeine, but these instances are very rare. I usually consume caffeine in the form of tea, because coffee makes my stomach upset. Generally, I've observed very little if any effects of caffeine.
Something I've also noticed, which may or may not be relevant, is that I'm also very minimally effected by morphine and anaesthasia. I received the first during a hospital visit following a horse riding accident and the latter for two dental surgeries. I expected to get 'high' off morphine like people always claim happens, but apart from pain removal I wasn't otherwise experiencing anything unusual. In the case of the aenasthasia, I woke up each time pretty much ready to go for a jog. No grogginess, nothing. During one of the procedures I woke up early while they were still tying the sutures and thought very clearly to myself, "Oh. They're not done yet. I guess I'll just wait." and sat back while the doctors realised I was conscious and discussed my wakefulness among themselves.
The only reason I mention this is because perhaps my lack of reaction to caffeine has more to do with my individual metabolism of substances than anything else. I really have no way of knowing.