An 8 week randomised, double-blind, placebo controlled trial investigating the role of adjunctive bioactive lipids specifically; docosahexaenoic acid (DHA) versus eicosapentaenoic acid (EPA) in Major Depressive Disorder - with a 6 week open label extension of DHA in patients aged 18-65years.

The primary objective is to evaluate the effectiveness of DHA versus placebo and compare the difference between DHA and EPA on the symptoms of depression. Effectiveness will be measured by the mean change in total scores on the HAM-D from baseline to double-blind end point at week 8. Patients with a 50% reduction in HAM-D scores or who have a score equal to or less than 8 will be considered to be in full remission whilst patients with a score of 12 or less will be considered to have improved; (from baseline to Week 8 or dropout). A secondary aim of the study will be to compare the levels of BDNF at baseline and at the completion of the double-blind phase of the study in the patients treated with DHA versus the comparator EPA and placebo. An additional aim will be to measure the change from baseline in cognitive functioning using a brief cognitive battery which assess 5 cognitive domains. Mean change from baseline scores to week 8 will also be used to measure patients Global Assessment of Functioning, sleep and levels of suicidal ideation using Item 3 on the HAM-D.