Some typical side effects of antidepressants are dry mouth, weight gain, and lack of sex drive. Some antidepressants may even cause infertility within both males and females depending on the extent of how long the medication was taken or how the body reacted to the medicine. Most types of antidepressants are typically safe to take, but may cause increased thoughts of suicide when taken by children, adolescents, and young adults. When prescribing antidepressants, doctors will warn individuals not to abruptly stop taking the medication or miss several doses at one time; this could cause major withdrawal-like symptoms, and quitting the medication suddenly can worsen the depression. Patients are instead encouraged to communicate and work with their doctors to wean themselves off the medication by gradually and safely decreasing the dosage when needed.
The most important classes of antidepressants are the 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), and noradrenergic and specific serotonergic antidepressant (NaSSAs). St John's wort is also used in the treatment of depression.
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. These HPA axis abnormalities participate in the development of depressive symptoms, and antidepressants may serve to regulate HPA axis function.
For depression, the Hamilton Depression Rating Scale (HAM-D) is often used to measure the severity of depression. The maximum score for the 17-item HAM-D questionnaire is 52; the higher the score, the more severe the depression.
The UK National Institute for Health and Care Excellence (NICE) 2009 guidelines indicate that antidepressants should not be routinely used for the initial treatment of mild depression, because the risk-benefit ratio is poor. The guidelines recommended that antidepressant treatment be considered for:
The guidelines further note that antidepressant treatment should be used in combination with psychosocial interventions in most cases, should be continued for at least six months to reduce the risk of relapse, and that SSRIs are typically better tolerated than other antidepressants.