The dosage ranged from 600 to 3,360 milligrams per day, and the studies lasted 4 to 16 weeks.

The results varied substantially across the studies (high heterogeneity). Greater improvements were observed in the following contexts:

Studies conducted in Asia
Dosages between 1,000 and 1,500 milligrams per day
Study lengths greater than 8 weeks
A eicosapentaenoic acid-to-docosahexaenoic acid] ratio of less than 2 to 1 or ratio not specified
Studies without baseline medication

Almost all of the analyses showed publication bias, and half of the studies had an unclear risk of bias.

Omega-3 fatty acids for depression? Original paper