The antidepressant Wellbutrin, which has the same active ingredient as GlaxoSmithKline PLC's Zyban, already carries such a warning. The FDA said it is also requiring an additional study on Champix and Zyban to determine the extent of the side-effects. Pfizer Inc., which makes Champix, said it is still discussing the potential study design with the FDA. The study could include patients with and without psychiatric conditions to determine the true incidence rate of psychological side-effects, Pfizer officials said. Pfizer had already updated its labeling following the beginning of an FDA investigation into the potential side-effects in 2007. That investigation was sparked by reports of about 37 suicides and more than 400 of suicidal behavior in connection with the drug.