Zoloft — I'll use the generic name for it, sertraline — could be the source of your problem, but the research won't tell us for sure.

Sertraline is one of the "SSRIs" (selective serotonin reuptake inhibitors). SSRIs have been associated with no weight gain or modest weight gain. But a few people do gain significant weight on sertraline.

The timing, as you describe it, is the best evidence. If you can link the beginning of the weight gain to when you started your treatment with sertraline, then I suggest you take the connection seriously and consider other options.

I'm assuming that you've gotten a good response from your treatment. That is, whatever you take sertraline for, you're getting relief. If that's true, you will not want to give up the good effects. Fortunately, many antidepressants may help you as much as sertraline. And some may help you without boosting your weight.

As a first step, you might ask your doctor to prescribe another SSRI — they are similar but not identical. Just because you've gained weight on one does not mean you will have the same trouble with another one.

Or your doctor, knowing the details of your situation, may recommend trying a different class of antidepressants. There is no way to predict which medication will be best for you. But I do think it is worth experimenting.

You will probably want to avoid mirtazapine (Remeron), because weight gain is one of its most common side effects. Older antidepressants — tricyclic antidepressants and monoamine oxidase inhibitors (MAOIs) — also commonly cause weight gain. These options may not cause weight gain in you, but I would try other medications first.

It is much easier to predict that exercising more and changing your diet will help you control your weight. It's not easy to make such changes, but one thing may motivate you: Exercise is good for your mental health too.