Oh yes.. it can definitely cause weight gain. I had lost 90lbs 3 yrs ago. I was on only Cymbalta at the time. Due to some family stress, he added Prozac [which is actually dangerous I later found out]. I gained 40lbs in 6 months. I was then put on Pristiq in January and gained more than 50lbs!
I have a new pdoc that has explained to me that ADs can not only make you eat everything in and including the fridge hungry, but they chemically put weight on you too. This, by no means, happens to everyone.. And there are ADs that are notorious for doing it, but everyone is different. I've read a lot of people who gained weight on Cymbalta, which I didn't. However, my father has been on Prozac for over 10 yrs and actually lost weight on it. As for the Pristiq.. I haven't heard a good thing about it.
Good luck to you!