Background: Questions have been raised about the internet's effect on mental health, although no principled review has yet tackled the issue.

Aims: To examine the effect of the internet on mental health.

Method: Literature review.

Results: The internet is typically discussed as if it were a set of activities when it is actually a medium upon which various activities can occur. It is, therefore, neither “good” nor “bad” for mental health, although specific activities may have an influence. The standard of mental health information on the internet is probably equivalent to the mainstream media, although overall it still remains poor. The concept of “internet addiction” looks increasingly invalid, although it is likely that depressed or isolated individuals are more likely to focus on certain activities to excess. A number of “extreme communities” have formed online, such as pro-anorexia, pro-suicide, pro-amputation and likely-psychotic groups. These serve to provide support, outside a medical and social mainstream that finds their beliefs and behaviours unacceptable. A review of preliminary randomized controlled trials shows online therapy to be effective for many disorders.

Conclusions: Mental health professionals are advised to lead the creation of online treatments and information. Clinical recommendations for the use of the internet are offered.

Declaration of interest: None.