Primary prevention

A World Psychiatric Association Commission on depression prevention has defined three levels of intervention: universal (aimed at a general population), selective (aimed at people who have known depression risk factors), and 'indicated' (targeted to people who already have some depressive symptoms, but not 'major' depressive illness).[28]​ These may be combined into a staged set of interventions tailored to a given organisation or group.

Psychological and educational interventions (including CBT) have been shown to modestly reduce the risk of progression to depression when targeted at adults at increased risk due to the presence of risk factors, as well as at those with subthreshold symptoms of depression.[113][114] One meta-analysis looking at CBT-based selective interventions for depression prevention (i.e., targeted towards those at increased risk of depression) found that such interventions were effective; 1 year after the preventive intervention, people had a relative risk of developing depression of 0.81 (95% CI: 0.72 to 0.91), meaning that those who had received the intervention had 19% lower chance of developing a depressive disorder compared to the control group. This corresponds to a number to treat (NNT) of 21, in order to prevent one episode of depression.[115]

Workplace interventions promoting employee control and physical activity, and those utilising CBT-based techniques, also show modest benefits.[116]​ Workplace interventions which use CBT to target people with subthreshold depressive symptoms have demonstrated small to medium effects.[117]​ eHealth interventions based on principles of CBT have demonstrated a small positive effect; one meta-analysis demonstrated that universal, selective and indicated eHealth interventions resulted in reduced rates of depression in the general population, although evidence on long-term efficacy is lacking.[118]

Preventative interventions which target lifestyle behaviours such as smoking also show promise for prevention.[119]​ Exercise has demonstrated antidepressant effects, and so may be a useful intervention to prevent progression to major depressive disorder for those with subthreshold symptoms.[120][121][122][123]​​​​​​

Secondary prevention

Patients and their families must be cautious during the early stages of medicine treatment, as the risk of suicide may temporarily increase. Routinely asking patients about suicidal ideation and reducing access to lethal means (especially firearms) can reduce the risk of suicide.[129] See Suicide risk mitigation.

Pre-emptive antidepressant treatment may prevent depression in medically ill patients, but evidence is uncertain.[484]

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