They say 4 to 6 weeks. I only took Prozac without a mood stabilizer and I swear I was off my rocker within 2 days and stayed on it for like 6 months crazy throughout. Other antidepressants effected me as quickly either on a mood stabilizer or not but, the Wellbutrin I take now had me nutty as all for several weeks and then BAM happy! Not that it helps but, like all psych meds give it a few weeks before deciding anything.