Hi there

I would definitely recommend talking to both the doctor who prescribes you the Effexor and the surgeon to talk about a possible connection between your weight gain and the Effexor. 

Here is what I am finding in the on-line literature.  This link is to a lengthy forum where many patients discuss how they fared with Effexor and particularly with relation to weight loss or gain.  It does seem to be a mixed bag of responses...some people lose weight but many people also report gaining weight on this drug and not being able to keep it off.

On eMedTV  they state that:  "Weight gain is a possible side effect of Effexor^® (venlafaxine hydrochloride), occurring in at least 1 percent of people who take the medicine (though the exact percentage was not reported). Weight loss is actually a more common Effexor side effect."

So once again, there is not a consensus as to whether or not you will lose or gain weight while taking this drug.  If it is a concern, as I have mentioned, discuss this with all doctors who are involved with your care. 

Good luck to you.  I hope you get to lose the weight.

Thank you for your question.