Antidepressants are drugs used for the treatment of major depressive disorder and of other conditions, including some anxiety disorders, some chronic pain conditions, and to help manage some addictions.Typical side-effects of antidepressants include dry mouth, weight gain, and lack of sex drive. Most types of antidepressants are typically safe to take, but may cause increased thoughts of suicide when taken by children, adolescents, and young adults. A discontinuation syndrome can occur after stopping any antidepressant. The risk is greater among those who have taken the medication for longer and when the medication in question has a short half-life. The problem usually begins within three days and may last for several months. Methods of prevention include gradually decreasing the dose among those who wish to stop, though it is possible for symptoms to occur with tapering.The most important classes of antidepressants are:
selective serotonin reuptake inhibitors (SSRIs)
serotonin norepinephrine reuptake inhibitors (SNRIs)
tricyclic antidepressants (TCAs)
monoamine oxidase inhibitors (MAOIs)
reversible inhibitors of monoamine oxidase A (RIMAs)
tetracyclic antidepressants (TeCAs)
noradrenergic and specific serotonergic antidepressant (NaSSAs)The plant St John's wort is also used in the treatment of depression.Bupropion, a NDRI, also operates as antidepressant.One theory regarding the cause of depression is that it is characterized by an overactive hypothalamic–pituitary–adrenal axis (HPA axis) that resembles the neuro-endocrine response to stress. HPA-axis abnormalities participate in the development of depressive symptoms, and antidepressants may serve to regulate HPA-axis function.The medical community has long debated the effectiveness of antidepressants, concentrating on whether one can attribute observed results in patients to the placebo effect.