Dr. David Lau, chairman of the diabetes and endocrine research group at the University of Calgary and president of Obesity Canada said that psychiatric drug-related weight gain "is a huge problem…you can see patients gaining 10, 20, 30, 40 pounds."

Dr. Lau however made it very clear that not everyone taking antidepressants, mood stabilizers or newer generation antipsychotics would gain weight. In fact, he added that new antipsychotics, so-called "atypical antipsychotics" have been "tremendous in terms of bringing back the functionality of people with schizophrenia, bipolar disorders and depression."

Dr.Lau listed the anti-psychotics most likely to be associated with weight gain as: Clozaril, or clozapine; Zyprexa, Seroquel or quetiapine; Risperdal, or risperidone; Modecate or chlorpromazine; fluphenazine and Haldol or haloperidol.

He explained further research was needed to establish the exact cause for weight. According to him, “some may stimulate appetite, while others may unmask a person's genetic propensity to gain weight, or cause the body to become resistant to insulin.”

Harvard University psychologist Paula Caplan traces a vicious cycle, where patients who experience weight gain after taking psychotropic drugs are reluctant to discontinue their use.  They would rather cut down on fast foods and think of exercising more, than discontinuing their use.

Writing in a recent article in the magazine New Scientist, Caplan says there have been new revelations that some antidepressants work merely as a placebo for all except the most severe cases of depression. According to her these "make the potential scale of the side effects more worrying than ever."