I once took a medication through a skin patch. The same issue: the generic did not deliver the medication consistently at all. The patch was supposed to be replaced every three days, so I'd get a huge rush of medication the first day and next to nothing the last day. What was worse was that there were two generics. One was as described, the other actually was fine.

The moral, for me, is to be very cautious with generics. I believe most of them are fine (I would never pay full price for Tylenol :), but the more critical the medication is to me, the more research I will do on the generic.