Omega-3 fatty acids — specifically the EPA-rich formulations — have meta-analytic evidence for depression treatment that places them among the few supplements with robust clinical data. The effect sizes are modest but real, particularly in patients with inflammation-elevated depression (Stage 10.5), bipolar depression, and as augmentation to standard antidepressant treatment. The clinical task is to prescribe the right dose, the right EPA:DHA ratio, and the right form — and to recognize the specific scenarios where omega-3 augmentation has the strongest evidence.
The EPA-to-DHA ratio matters substantially. Meta-analyses consistently show that formulations with EPA at >60% of total omega-3 produce antidepressant effects; formulations dominated by DHA show minimal benefit in depression. The mechanism appears to be EPA-derived anti-inflammatory eicosanoids and specialized pro-resolving mediators (resolvins, protectins). The clinical implication is that not all "fish oil" is equivalent — the prescription must specify EPA-predominant formulation. Most over-the-counter fish oils are not in the right ratio; product selection matters.
The dose with evidence is substantial. Typical effective regimen is 1000–2000 mg EPA daily plus 500–1000 mg DHA — total omega-3 in the 1.5–3 gram range, which often requires multiple capsules of even well-formulated products. Lower doses (500mg EPA or less) have minimal evidence. The prescription that says "take an omega-3 supplement" without specifying dose and EPA content frequently produces inadequate intake.
The strongest indications are clear. Inflammation-elevated depression (hs-CRP >3 mg/L) shows the largest effect sizes in subgroup analyses. Bipolar depression has positive data for omega-3 augmentation. SSRI augmentation in TRD with partial response shows modest benefit. Pregnancy and postpartum depression have specific evidence given the safety profile in pregnancy and the maternal omega-3 needs. Other indications (anxiety, schizophrenia, ADHD) have less robust evidence but reasonable case for use.
The practical prescribing. Specify the brand and dose — many clinicians find generic recommendations produce inconsistent intake. Triglyceride-form omega-3 (rTG) may have somewhat better absorption than ethyl ester form but the cost difference is real. Quality matters — third-party testing (USP, NSF, IFOS) addresses purity concerns about heavy metals and oxidation. Start at full dose; titrate down only if GI tolerability requires. Monitor effect over 6–12 weeks. Omega-3 is one of the few supplements with enough evidence to write a real prescription; the clinical work is to prescribe it specifically rather than recommend it generically.