Omega-3 fatty acids — particularly eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) — are long-chain polyunsaturated fatty acids (PUFAs) essential for human brain structure and function. They are classified as "essential" because the human body cannot synthesize them from scratch; they must be obtained from dietary sources (primarily fatty fish, krill, or algae) or supplementation. Alpha-linolenic acid (ALA, C18:3n-3), found in plant sources like flaxseed and walnuts, is the metabolic precursor to EPA and DHA but is converted at very low efficiency (typically <5% to EPA and <0.5% to DHA) — making direct EPA and DHA consumption from marine sources essential for maintaining adequate brain levels.
DHA is the most abundant polyunsaturated fatty acid in the brain, comprising approximately 30–40% of total fatty acids in the neuronal membrane phospholipids of the cerebral cortex. Its structural role in neuronal membranes is fundamental: DHA's six double bonds create a highly flexible, fluid membrane microenvironment that is essential for optimal receptor function, ion channel kinetics, signal transduction, and neurotransmitter release. Neurons are literally built from DHA, and the brain's voracious demand for DHA during fetal development and early childhood — when synaptic connections are being established at extraordinary rates — underscores its biological importance.
EPA has a distinct profile: while DHA is primarily structural, EPA is primarily bioactive — it is the precursor to anti-inflammatory eicosanoids (prostaglandins, thromboxanes, and leukotrienes of the 3-series) and specialized pro-resolving mediators (SPMs) including resolvins and protectins that actively terminate inflammation. EPA's anti-inflammatory effects, and evidence from randomized trials for antidepressant efficacy, have made it a focus of psychiatric pharmacology research. Pure EPA preparations at doses of 1–4 g/day have demonstrated antidepressant efficacy in multiple controlled trials, including as augmentation of antidepressants — EPA appears to be the more relevant omega-3 fatty acid for mood.
In harm reduction contexts, omega-3s are relevant as foundational neuroprotective supplements used before, during, and after cycles of drug use; as core components of the "Mr. Happy Stack" (with uridine and choline, promoting synaptogenesis); and as anti-inflammatory agents with particular relevance to the neuroinflammation associated with heavy drug use and withdrawal.