There is one simple explanation for those extra pounds of weight. Too much food! The way the body works is very simple. If you get just enough calories for basic things like breathing, you have to burn fat to get the energy to walk around. Eat more calories than you need given your basal activity level, and your body puts on fat. Your body is actually protecting you against the next famine when you will have nothing to eat and need your fat to survive until the next sandwich comes along.

Now turn to many of the forum sites where people discuss their experience with zoloft. The general spirit of these posts is, "I weighed 120lb until I took zoloft. Now I am . . ."

A simple test rules out thyroid problems, one of the more common physical explanations for sudden weight gains and this leaves us with lack of exercise combined with overeating. . . and a side effect of zoloft. It is a natural association to make. You start taking a medication and immediately you put on five pounds with no obvious change in your diet or level of physical activity. So, let us start off by accepting that some people react to medications by putting on weight. Why? The medication may increase or decrease the basal metabolic rate. If this happens, your weight may fluctuate even though you do not change your caloric intake. In some people, the medication can cause hormonal changes and increase appetite. Increased levels of serotonin are also associated with hunger pangs which encourage you to eat more.

Now we are into the business of balancing the advantages and disadvantages of the particular medication. Let us say that zoloft has made a dramatic improvement in your emotional life. For the first time in months (or years), you do not feel (so) sad. If you have put on a few extra pounds, is that a price worth paying? Or will you get depressed again because your body has become less attractive? As a gentle warning, if your regular doctor asks you whether you want to try a different medication, zoloft causes less weight gain than the tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs).

Back to denying the link. After all, the SSRIs were first promoted as anti-obesity medications. Like all decisions on whether to start a medication, you are dealing with unknowables. There is no doubt that some people eat more when they are depressed. Unless you have been keeping a food diary which counts calories, it will difficult to know how your eating habits have changed as the depression increased in intensity. You may already be putting on weight when you start taking the zoloft. Now let us reverse the psychological reaction. When people start feeling less depressed, they eat less and this reduces their weight. In other words, when the depression is cured, you may return to your healthy eating habits. Separating out the effect of the medication from the reality of the number of calories you eat is very difficult. It is easy to confuse coincidence with side effect.

So how should you react if you start zoloft and gain weight? Whatever else you may do, do not stop taking it. First, start counting calories properly. Start exercising. These are most likely to stabilise your weight. Only if you do change your diet and exercise to no effect, should you talk with your doctor. If self-help has failed, see what the professional recommends.