Weight gain has been reported with nearly every antipsychotic drug on the market 
(molindone is an exception). Weight gain occurs no matter what the patient's 
age, sex, or race and is seen with both oral and depot drug formulations. 
Numerous studies have found that patients gain weight when treated with a 
conventional antipsychotic, such as chlorpromazine, fluphenazine, and 
haloperidol. The newer, novel antipsychotics offer advantages over conventional 
antipsychotics, especially a relative lack of extrapyramidal symptoms, but some 
still have the disadvantage of causing weight gain. Clozapine and olanzapine in 
particular appear to cause substantial weight gain, much more so than do most 
conventional neuroleptics and novel agents such as risperidone. Given the risks 
to health and treatment compliance associated with weight gain and obesity, 
clinicians should monitor weight during the course of antipsychotic therapy and 
consider switching agents if excessive weight gain occurs.