I have taken the generic forms of other medications and have not noticed a noticable difference (except in my wallet...which was a positive difference). Also, I assume you would discuss any changes in dosage with your prescrbing doctor first. It is not smart to self-medicate with drugs like these...keep us posted!
I just want to understand your question a little better. Have you been on a different medication that has made you gain weight? I assume you are taking it for anxiety/depression correct?
I take wellbutrin 300, previously 150, and I take the generic form of it. During my last anxiety episode I lost 12 pounds in 3 weeks and I was down to a weight of 120. That was in May. Now it is October and I have gained some of it back but not all of it, probably about half. I don't think that it is going to make you lose huge amounts of weight but rather it is not going to bloat you and make you gain weight, at least from my experience. Of course eating habits and exercise always play a role as well.
When I went from 150 to 300 I suffered side effects that lasted at least 4 weeks. They were not pleasant and I needed to take klonopin to get through them...so there is that aspect of a dosage increase as well. I'm not saying that happens to everyone but rather just sharing my own experience with the increase.
http://www.livestrong.com/article/382396-information-about-wellbutrin-for-weight-loss/