Research has shown that Omega-3 fatty acids, especially the long-chain forms, EPA and DHA which are found in fish oil are helpful for people with inflammatory arthritis, such as rheumatoid arthritis, ankylosing spondylitis and psoriatic arthritis. Long-chain forms are found in salmon, sardines, mackerel and tuna.

Fish oil supplements are available in liquid or capsule form with bottled fish oil the most convenient and least expensive way to take the dose required to reduce inflammation.  The daily dose needed to reduce inflammation is 2.7g of omega-3 (EPA plus DHA) daily. Because fish oil acts slowly it may be necessary to give them a two to three months trial before an improvement is evident.  Trials on fish oil for osteoarthritis have so far been inconclusive.  While fish oil is usually well tolerated some people may experience an upset stomach. Dividing the dose into two or three smaller doses  may help.  People on warfarin should seek advice from their GP before taking fish oil.

There is evidence that taking fish oil over a long time can reduce reliance on non-steroidal anti-inflammatory drugs (NSAIDs) in some cases of arthritis.