The study will be a 4 week, parallel-group double blind randomised control trial of the efficacy pf Omega-3 as an augmentor of antidepressant treatment for depression. People aged between 18 and 65 with a first or new episode of depression warranting treatment with antidepressant medication will be recruited. In addition to their antidepressant medication, participants will be randomly allocated to receive either Omega-3 (fish oil) or placebo (paraffin oil)for 4 weeks. Participants will commence treatment with the antidepressant and Omega-3/placebo simultaneously. Participants will be followed up at 1,3 and 4 weeks and will be asked to rate their mood daily for the 4 week study period. Blood samples will be taken pre and post treatment to measure change in Omega-3 levels.