Antidepressants are usually taken every day. It can take up to a month to see the full results of taking an antidepressant. Sometimes different kinds or amounts (dosages) need to be tried to find one that works best for you. Antidepressants are typically taken for at least 6 to 12 months. In some cases, patients and their doctors may decide that antidepressants are needed for a longer time.