While there are worse offenders than Zoloft, it is possible to gain weight on all the SSRI's. Some people do OK on Prozac. If you want to stay on an antidepressant, you might try Wellbutrin, Effexor, or Cymbalta, which are in a slightly different class than Zoloft. I gained 50 pounds on Paxil, and I wouldn't let that happen again. I think you're right to be concerned.