TUESDAY, March 12 (HealthDay News) -- For people who don't fully respond to antidepressants, adding commonly prescribed antipsychotic drugs appears to be only slightly effective and is linked to unwelcome side effects, a new study finds.

Drugs added to antidepressants (like Prozac, Paxil and Celexa) include the antipsychotic medications aripiprazole (Abilify), quetiapine (Seroquel), risperidone (Risperdal) and olanzapine/fluoxetine (Symbyax).

Antipsychotic drugs are traditionally used to treat conditions such as schizophrenia, bipolar disorder and obsessive-compulsive disorder -- not depression.

"The evidence supporting the use of antipsychotics in depression is marginal," said lead researcher Glen Spielmans, an associate professor in the department of psychology at Metropolitan State University in St. Paul, Minn.

Antipsychotic treatment of depression has become increasingly widespread but the underlying evidence base puts this practice into question, he said.

"Other options may be as effective, or more effective, and carry a lesser side-effect burden," Spielmans said. For instance, cognitive behavioral therapy has been shown to be effective for treatment-resistant depression, he said. Cognitive behavioral therapy is a treatment that helps patients try to change their thoughts, feelings and behaviors.

For one expert, these drugs also aren't a first choice for patients who don't respond fully to antidepressants.

"I have mixed results in terms of how effective they are," said Dr. Bryan Bruno, acting chair of psychiatry at Lenox Hill Hospital, in New York City.

"I treat a lot of patients who are on antidepressants and not responding well. Prescribing these drugs is not something I do often because of the costs and because of the side effects," said Bruno, who was not involved with the study.

Some of these drugs are pricey. For example, Abilify can cost more than $200 a month without insurance, according to the Everyday Health website. With insurance the cost varies by plan.

"I prefer using other strategies like adding other antidepressants, or using brain stimulation treatments, and psychotherapy," Bruno said.

For some patients, however, these antipsychotics can be helpful, including those with insomnia and those whose depression is coupled with a psychosis, he noted.