Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is found in high concentrations in the brain and is vital for normal neuronal function. The rationale for its use in Alzheimer's Disease (AD) stems from observational studies showing lower levels of DHA in the brains and plasma of AD patients, as well as experimental data suggesting neuroprotective, anti-inflammatory, and membrane-stabilizing roles for DHA in neural tissue. Some epidemiological research has found associations between higher dietary or plasma DHA and reduced risk of cognitive decline or AD. However, randomized controlled trials (RCTs) evaluating DHA supplementation in individuals with established AD have produced mixed or negative results. For example, the large, well-designed Alzheimer's Disease Cooperative Study (ADCS) trial (Quinn et al., JAMA 2010) found no significant cognitive benefit of DHA supplementation in mild to moderate AD over 18 months. Some subgroup analyses and studies in preclinical or prodromal stages of cognitive impairment suggest a potential benefit if DHA is started early, but robust evidence in diagnosed AD is lacking. As a result, while the use of DHA is scientifically motivated, the clinical evidence supporting its efficacy as a treatment for Alzheimer's Disease is currently weak to modest at best.