Fish oil

How long does fish oil take to work?

Updated 4 Nov 2026

Short answer

It depends on the outcome. Blood levels of EPA and DHA rose within 2 weeks in a study that gave about 3.3 g a day.[1] Red blood cell levels reflect intake over about the last 120 days.[2]

In a 12-week trial, 4 g of purified EPA a day lowered triglycerides by 21.5%.[3] In a trial in rheumatoid arthritis, people needed fewer anti-inflammatory painkillers (NSAIDs) from month 3, with the largest effect at month 12.[4]

Trials on heart disease followed people for 3.5 to 7.4 years.[5][6]

Sources (6)

  1. Bioavailability of marine n-3 fatty acid formulations. Dyerberg J, Madsen P, Møller JM, Aardestrup I, Schmidt EB Prostaglandins Leukot Essent Fatty Acids, 2010. PMID 20638827
  2. Omega-3 Fatty Acids: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  3. Efficacy and safety of eicosapentaenoic acid ethyl ester (AMR101) therapy in statin-treated patients with persistent high triglycerides (from the ANCHOR study). Ballantyne CM, Bays HE, Kastelein JJ, Stein E, Isaacsohn JL, Braeckman RA, et al. Am J Cardiol, 2012. PMID 22819432
  4. Effects of fish oil supplementation on non-steroidal anti-inflammatory drug requirement in patients with mild rheumatoid arthritis--a double-blind placebo controlled study. Lau CS, Morley KD, Belch JJ Br J Rheumatol, 1993. PMID 8220938
  5. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto miocardico. Lancet, 1999. PMID 10465168
  6. Effects of n-3 Fatty Acid Supplements in Diabetes Mellitus. Bowman L, Mafham M, Wallendszus K, Stevens W, Buck G, Barton J, et al. N Engl J Med, 2018. PMID 30146932

More about fish oil

What is fish oil?Does fish oil reduce inflammation?How much EPA and DHA is in a fish oil capsule?Is eating fish better than taking fish oil?What is fish oil used for?Should fish oil be taken with food?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.