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). I have been tapering off Effexor and I am horrified by the weight gain I am experiencing. I haven't changed my eating habits at all and yet keep gaining weight as I reduce the Effexor. Panic! I haven't changed my eating habits at all and yet keep gaining weight as I reduce the Effexor. Ive been on Venlafaxine which is a substitute for Effexor 150mg for 2 years now. Noticed a weight gain of 25 to 30 pounds. not happy about that since I hardly eat anything. but noticed an increase in sugar cravings. I am also quite active so why is the weight not coming off. I am also more miserable than ever and fat too. This is not good for me as because of the weight gain, Iv called my. A: According to the package insert, Effexor (venlafaxine) may cause weight gain. There are other factors that can affect body weight. Some of these include chronic stress, hypothyroidism, poor. I have been on effexor 225mg for a year. Yes I am less depressed and have less anxiety but it has left me a somewhat apathetic which makes me less carefull in many aspects of my life and I wonder if this causes weight gain and loss in people taking it. Effexor (Venlafaxine) is a common antidepressant medication that is classified as an SNRI. It functions by preventing reuptake of the neurotransmitters serotonin and norepinephrine. Summary. It is possible for patients taking Effexor to experience weight gain, but only in about 1% of patients. It is more common tat they will experience weight loss: on average, an individual taking Effexor will lose 1-2 pounds at the onset of treatment, and possible much more down the line. Venlafaxine, sold under the brand name Effexor, is an anti-depressant medication. Effexor is a serotonin-norepinephrine reuptake inhibitor, or SNRI. It's a class of drugs that target the neurotransmitters serotonin and norepinephrine in your brain. Although Effexor can cause weight gain, it is less I have put on masses of weight with Effexor. I try to eat sensibly, but find the weight hard to lose. I stopped the drug for a year and lost all the weight gain.