Basic treatment for mild, moderate, and severe depression and the depressed phase of bipolar illness is generally similar. The principal decision is to decide whether drugs or psychotherapy or a combination of both is preferred. Surveys have shown that most of the patients in primary care would prefer psychotherapy rather than medicines, but evidence of effectiveness is limited only to some forms of psychotherapy.

For mild to moderate depression, cognitive-behaviour therapy and anti-depressants are considered to be equally effective. For more severe depression, antidepressant medicines are more effective. In mild depression patients' response to tricyclic antidepressants may be no better than placebo, but this may be related to the patients' incompliance.

Antidepressants can improve or completely relieve the symptoms of depression. Several medication options are available, depending on the patients' age and tolerance of the medications. There is no evidence that one medication works better than another; however, the side effects of the medications differ.

A combination of antidepressants and psychotherapy can be more effective than each method alone. In particular, antidepressants can be a condition for success with psychotherapy.