I have recently discovered that sometimes the fillers in drugs can cause funny reactions in people sensitive to them. You may have taken the name brand
Wellbutrin without a problem and then react funny to the generic because of one of the fillers, it may be an allergy or just some sensitivity that can interfere with how the drug itself works for you.
I had never even thought of this until I switched pharmacies after we moved and the new one carried a generic of my birth control. I had used it for years since having my son without any problems and suddenly I was having cramps, heavy bleeding, diarhhea and usually bleeding 3 weeks instead of just one. I did try it for three months to try to let my body adjust to the change but I still had all the same problems.
On my next appointment I talked to my doc and she wrote a new prescription with "brand medically necessary" on it and told me about the filler problem. It it not extremely common but it does happen to some people. Since switching back to the name brand I am doing fine again with no problems.