- EPA and its metabolites act in the body largely by their interactions with the metabolites of arachidonic acid; see Essential fatty acid interactions for detail.
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Eicosapentaenoic acid (EPA or also icosapentaenoic acid) is an omega-3 fatty acid. In physiological literature, it is given the name 20:5(n-3). It also has the trivial name timnodonic acid. In chemical structure, EPA is a carboxylic acid with a 20-carbon chain and five cis double bonds; the first double bond is located at the third carbon from the omega end.
It is obtained in the human diet by eating oily fish or fish oil— e.g., cod liver, herring, mackerel, salmon, menhaden and sardine, and various types of edible seaweed. It is also found in human breast milk.
However, fish do not naturally produce EPA, but obtain it from the algae they consume. It is available to humans from some non-animal sources (e.g., commercially, from microalgae). Microalgae are being developed as a commercial source. EPA is not usually found in higher plants, but it has been reported in trace amounts in purslane.
The human body converts alpha-linolenic acid (ALA) to EPA. ALA is itself an essential fatty acid, an appropriate supply of which must be ensured. The efficiency of the conversion of ALA to EPA, however, is much lower than the absorption of EPA from food containing it. Because EPA is also a precursor to docosahexaenoic acid (DHA), ensuring a sufficient level of EPA on a diet containing neither EPA nor DHA is harder both because of the extra metabolic work required to synthesize EPA and because of the use of EPA to metabolize DHA. Medical conditions like diabetes or certain allergies may significantly limit the human body's capacity for metabolization of EPA from ALA.
Clinical significance 
The US National Institute of Health's MedlinePlus lists medical conditions for which EPA (alone or in concert with other ω-3 sources) is known or thought to be an effective treatment. Most of these involve its ability to lower inflammation.
Among omega-3 fatty acids, it is thought that EPA in particular may possess some beneficial potential in mental conditions, such as schizophrenia. Several studies report an additional reduction in scores on symptom scales used to assess the severity of symptoms, when additional EPA is taken.
Studies have suggested that EPA may be efficacious in treating depression. One 2004 study, took blood samples of 100 suicide attempt patients and compared the blood samples to those of controls and found that levels of eicosapentaenoic acid were significantly lower in the washed red blood cells of the suicide-attempt patients. A 2009 metastudy found that patients taking omega-3 supplements with a higher EPA:DHA ratio experienced less depressive symptoms. 
In a study published in 2011, EPA was shown to be significantly more effective than placebo for treating hyperactivity and attention symptoms, both together and separately.
 A 2011 study describes, for the first time, a prominent protection by EPA against valproate (VPA)-induced hepatic dysfunction, necrosis, and steatosis. Given that VPA is commonly used in mood disorders, this may offer protection against intentional or unintentional overdose. Further, this same study showed a synergistic effect on raising seizure threshold (in pentylenetetrazol mouse convulsion model) when EPA and VPA are used concomitantly.
- Yvonne Bishop-Weston. "Plant based sources of vegan & vegetarian Docosahexaenoic acid - DHA and Eicosapentaenoic acid EPA & Essential Fats". Retrieved 2008-08-05.
- Jess Halliday (12/01/2007). "Water 4 to introduce algae DHA/EPA as food ingredient". Retrieved 2007-02-09.
- Simopoulos, Artemis P (2002). "Omega-3 fatty acids in wild plants, nuts and seeds". Asia Pacific Journal of Clinical Nutrition 11 (Suppl 2): S163–73. doi:10.1046/j.1440-6047.11.s.6.5.x.
- Plant based sources of vegan & Vegetarian DHA & EPA and Omega 3 essential fatty acids
- NIH Medline Plus. "MedlinePlus Herbs and Supplements: Omega-3 fatty acids, fish oil, alpha-linolenic acid". Retrieved February 14, 2006.
- Peet M, Brind J, Ramchand CN, Shah S, Vankar GK (2001). "Two double-blind placebo-controlled pilot studies of eicosapentaenoic acid in the treatment of schizophrenia". Schizophrenia Research 49 (3): 243–51. doi:10.1016/S0920-9964(00)00083-9. PMID 11356585.
- Song C, Zhao S (Oct 2007). "Omega-3 fatty acid eicosapentaenoic acid. A new treatment for psychiatric and neurodegenerative diseases: a review of clinical investigations". Expert Opin Investig Drugs 16 (10): 1627–38. doi:10.1517/135437188.8.131.527. PMID 17922626.
- Huan M, Hamazaki K, Sun Y, Itomura M, Liu H, Kang W, Watanabe S, Terasawa K, Hamazaki T. (2004). "Suicide attempt and n-3 fatty acid levels in red blood cells: a case control study in China" (abstract). Biological Psychiatry 56 (7): 490–6. doi:10.1016/j.biopsych.2004.06.028. PMID 15450784.
- Martins, J. G. (2009). "EPA but not DHA appears to be responsible for the efficacy of omega-3 long chain polyunsaturated fatty acid supplementation in depression: Evidence from a meta-analysis of randomized controlled trials". Journal of the American College of Nutrition 28 (5): 525–542. PMID 20439549.
- Yao HT, Chang YW, Lan SJ, Chen CT, Hsu JT, Yeh TK (2006). "The inhibitory effect of polyunsaturated fatty acids on human CYP enzymes". Life Sci. 79 (26): 2432–40. doi:10.1016/j.lfs.2006.08.016. PMID 16978661.
- Hardman,W Elaine (2004). "(n-3)Fatty Acids and Cancer Therapy". Journal of Nutrition 134 (12): 3427S. PMID 15570049.
- Journal of American Academy of Child and Adolescent Psychiatry 2011 Oct; 50:991
- Biochim Biophys Acta 2011 Jul-Aug;1811(7-8):460-7. Eicosapentaenoic acid ablates valproate-induced liver oxidative stress and cellular derangement without altering its clearance rate: Dynamic synergy and therapeutic utility. El-Mowafy A;Abdel-Dayem M;Abdel-Aziz A;El-Azab M;Said S. Pubmed: 21571092