Quick answer: Long-chain omega-3 fats (EPA and DHA) from oily fish or fish oil can modestly reduce joint tenderness and morning stiffness in rheumatoid arthritis, but they work slowly and do not replace medicines. Evidence for osteoarthritis is weak. Eat oily fish at least once a week, and check with a doctor or pharmacist before taking fish oil if you use blood thinners or NSAIDs.
Evidence checked on 10 October 2026 against Arthritis UK's fish oils information, the BDA omega-3 fact sheet, NHS fish guidance and the trials listed below.
Of all the supplements people with arthritis ask about, fish oil has the most research behind it. That does not mean it works for everyone, or for every type of arthritis. This review explains what omega-3 fats are, what the studies show, how food compares with supplements, and how to use fish oil safely if you decide to try it.
What are omega-3 fats?
Omega-3s are a family of polyunsaturated fats. The BDA explains the main types:
- ALA (alpha-linolenic acid): an essential fat found in plant foods such as walnuts, flaxseed (linseed), chia seeds and rapeseed oil.
- EPA and DHA: long-chain omega-3s found mainly in fish, especially oily fish. Your body can make small amounts from ALA, but this happens slowly.
Most arthritis research has looked at EPA and DHA from fish oil. These are thought to reduce the production of some substances involved in inflammation, which is why they have been studied in inflammatory arthritis.
Evidence in rheumatoid and other inflammatory arthritis
Arthritis UK (formerly Versus Arthritis) summarises the evidence like this:
- A report combining data from 10 trials found that fish body oil reduced the number of tender joints and shortened morning stiffness compared with placebo, but did not significantly change other measures such as grip strength, blood tests for disease activity or overall severity. The trials were of low to moderate quality.
- A review of 17 randomised trials, using doses of about 1.6 to 7.1g of omega-3 a day, found fish oil was generally well tolerated and reduced joint pain, morning stiffness, the number of tender or swollen joints and the use of painkillers.
- Arthritis UK's overall conclusion is that marine oils can modestly reduce pain and inflammation in rheumatoid arthritis and may reduce the need for painkillers.
Arthritis UK also says omega-3 can be helpful in other inflammatory types of arthritis, such as psoriatic arthritis, reactive arthritis and axial spondyloarthritis. It notes that fish oils act slowly, so it suggests trying them for about three months to judge any benefit.
What this means in practice: fish oil is a reasonable thing to try alongside your prescribed treatment if your rheumatology team agrees. It is not a substitute for disease-modifying medicines, which protect your joints from long-term damage. NICE guidance on rheumatoid arthritis (NG100) says complementary therapies should not replace conventional treatment.
Evidence in osteoarthritis
The evidence for osteoarthritis is much weaker:
- An Australian trial in knee osteoarthritis (Hill and colleagues, 2016) compared a high dose of fish oil with a low dose. There was no extra benefit from the high dose. Unexpectedly, the low-dose group did slightly better on pain at two years, which the authors said needs more research.
- A 2024 trial in JAMA (Laslett and colleagues) found that 2g a day of krill oil, another source of omega-3, did not improve knee pain over 24 weeks compared with placebo in people with knee osteoarthritis and joint inflammation on MRI.
- Arthritis UK says there is no evidence that cod liver oil makes a difference to osteoarthritis.
So for osteoarthritis, the most effective things remain exercise and, if relevant, weight management, as NICE guidance NG226 recommends. Omega-3 from oily fish is still good for your heart, which is a sensible reason to eat it.
Why omega-3 matters for your heart too
The NHS says long-chain omega-3 can help to prevent heart disease. Arthritis UK points out that omega-3 fats also help lower cholesterol and triglyceride levels, which may reduce the risk of heart disease and stroke in people with inflammatory arthritis, who have a higher risk of these conditions. This is a good reason to eat oily fish regularly even if it makes no obvious difference to your joints. It fits naturally into an anti-inflammatory, Mediterranean-style diet.
Can omega-3 prevent arthritis?
The large VITAL trial in older US adults (Hahn and colleagues, BMJ 2022) tested omega-3 supplements for preventing autoimmune diseases, including rheumatoid arthritis. The omega-3 group had fewer new autoimmune diagnoses than the placebo group, but the difference was not statistically significant, so it does not show that fish oil prevents arthritis.
Evidence at a glance
| Condition | Evidence | Bottom line |
|---|---|---|
| Rheumatoid arthritis | Several trials and reviews; benefits modest | May reduce tender joints, stiffness and painkiller use. Try for about 3 months alongside treatment |
| Other inflammatory arthritis | Less research | Arthritis UK says it can be helpful; discuss with your team |
| Osteoarthritis | Trials mostly negative or uncertain | Not expected to ease joint pain; eat oily fish for heart health |
| Gout | Not a recommended treatment | Ask your GP or a dietitian about oily fish in your diet |
Food first: oily fish
UK guidance is food first. The NHS advises at least 2 portions of fish a week (a portion is about 140g), 1 of which should be oily. Oily fish includes:
- salmon, trout and mackerel
- sardines, pilchards and herring (including kippers)
- anchovies and sprats
Fresh and tinned tuna do not count as oily fish. Tinned fish is cheap, keeps well and needs no preparation, which helps on bad days. Tinned sardines, pilchards and salmon with soft bones also provide calcium.
How much is too much?
The BDA says that if you are past childbearing age or not planning to have children, you can eat up to four portions of oily fish a week. If you are pregnant, breastfeeding, planning a pregnancy or may become pregnant in future, the limit is two portions a week, because of pollutants. Avoid shark, swordfish and marlin if you are pregnant, planning a pregnancy or under 16, because of mercury.
If you do not eat fish
You can get ALA from walnuts, ground flaxseed, chia seeds, rapeseed oil and some fortified foods. Arthritis UK notes that we do not know whether plant omega-3s are as beneficial as the EPA and DHA in fish oil. Algae-based omega-3 supplements contain EPA and DHA and are suitable for vegetarians and vegans; the omega-3 in fish originally comes from algae.
For meal ideas, see our simple oily fish meals and our guide to oily fish and arthritis.
If you choose a supplement
Fish oil is not the same as fish liver oil
This is the most important point. Fish body oil comes from the flesh of oily fish. Fish liver oil, such as cod liver oil, also contains vitamins A and D. Arthritis UK warns that large doses of fish liver oil could lead to too much vitamin A, which can cause liver problems and is particularly dangerous in pregnancy. The BDA says you should not have more than 1.5mg (1,500 micrograms) of vitamin A a day from food and supplements combined, and should not take supplements containing vitamin A if you are pregnant or planning a pregnancy.
If you want omega-3 for arthritis, Arthritis UK recommends pure fish oil rather than fish liver oil.
Doses
Doses vary a lot, and labels can be confusing. Look at the amount of EPA plus DHA, not the total amount of oil in each capsule.
- The BDA notes that omega-3 supplements are not recommended for the general population, because evidence of benefit is inconclusive. If you choose one for general health, it suggests a daily adult dose of about 450mg of EPA and DHA, similar to eating one to two portions of oily fish a week.
- For inflammatory arthritis, Arthritis UK says quite large amounts are needed for the best effects and mentions concentrated products providing 3g of EPA and DHA a day. Trials have used about 1.6 to 7.1g a day.
Because higher doses have more potential for side effects and interactions, agree a dose with your rheumatology team, GP or pharmacist rather than choosing one yourself.
Reading a label: a worked example
A capsule might say "1000mg fish oil" on the front. On the back, the nutrition panel might show that each capsule contains 180mg EPA and 120mg DHA, which is 300mg of EPA plus DHA. So reaching a particular amount of EPA and DHA could take several capsules a day. Concentrated "omega-3" products contain more EPA and DHA per capsule, which means fewer capsules but usually a higher price. Always compare the EPA plus DHA content, the number of capsules per daily dose and whether vitamin A is included.
Quality and storage
Fish oil can go rancid, which may cause a fishy taste or burps. Store it as the label says, check the use-by date, and do not buy more than you will use in a few months. Arthritis UK notes that very high doses of fish oil raise concerns about environmental contaminants, and that most supplement companies test their products for purity.
Side effects
Arthritis UK says side effects are usually minor, most commonly stomach upset, with wind or diarrhoea in some people. Taking the dose in two or three smaller amounts with meals can help.
Important safety: blood thinners and NSAIDs
Arthritis UK advises that people taking blood-thinning medicines, such as warfarin, apixaban, rivaroxaban or aspirin, or anti-inflammatory painkillers, should seek medical advice before using fish oil, because it can increase the risk of bleeding.
- Warfarin: the NHS says to tell your doctor if you take any vitamins or supplements and to speak to your doctor before starting new ones. Your INR may need checking.
- NSAIDs such as ibuprofen and naproxen can already cause stomach bleeding. Adding something else that affects bleeding needs a conversation with your pharmacist.
- Before surgery or dental extractions: tell the team you take fish oil.
- Allergy: if you are allergic to fish, avoid fish oil and ask about algae-based alternatives.
Our full guide to medicine and supplement interactions covers other combinations.
How to try fish oil sensibly
- Talk to your rheumatology team, GP or pharmacist, especially if you take any blood thinner or NSAID.
- Choose pure fish oil (or algae oil), not fish liver oil, and check the EPA and DHA content.
- Write down your symptoms before you start: morning stiffness, number of painful joints, painkiller use.
- Take it consistently for about three months.
- Review your notes. If you cannot see a difference, it is reasonable to stop and save the money.
- Do not stop or reduce prescribed medicines without talking to your team.
When to see a dietitian
A registered dietitian can help if you do not eat fish, have a fish allergy, follow a vegan diet, have gout, or are trying to balance fish intake with pregnancy plans. Ask your GP or rheumatology team about a referral.
When to get medical help
Stop fish oil and get urgent medical advice if you notice signs of bleeding, such as black or bloody stools, vomiting blood, blood in your urine, or unusual bruising, especially if you take a blood thinner. Speak to your GP or rheumatology team if your arthritis is getting worse, rather than increasing supplements. Get same-day advice from your GP or NHS 111 if a joint suddenly becomes hot, swollen and very painful, especially with a fever.
Frequently asked questions
Does fish oil help rheumatoid arthritis?
It can modestly reduce joint tenderness, morning stiffness and painkiller use for some people, according to reviews summarised by Arthritis UK. It works slowly and does not replace disease-modifying medicines.
Does fish oil help osteoarthritis?
The evidence is weak. Trials of fish oil and krill oil in knee osteoarthritis have not shown clear benefits. Exercise and weight management are more effective.
Is cod liver oil good for arthritis?
Arthritis UK says there is no evidence that cod liver oil helps osteoarthritis, and large doses risk too much vitamin A. Choose pure fish oil if you want omega-3.
Can I take fish oil with warfarin?
Only after speaking to your doctor or anticoagulant clinic. Fish oil can increase bleeding risk, and your INR may need closer monitoring.
How long does fish oil take to work?
Arthritis UK suggests trying it for about three months before deciding whether it helps.
Is eating oily fish better than taking a supplement?
UK advice is food first. Oily fish also provides protein, vitamin D, selenium and, in tinned fish with bones, calcium. Supplements may help if you want the higher doses used in inflammatory arthritis trials, with medical advice.
Sources and further reading
- Arthritis UK: Fish oils
- Arthritis UK: Diet and nutritional supplements (omega-3)
- BDA: Omega-3 food fact sheet
- NHS: Fish and shellfish
- Hill CL et al. Fish oil in knee osteoarthritis: a randomised clinical trial of low dose versus high dose. Ann Rheum Dis 2016 (PMID 26353789)
- Laslett LL et al. Krill oil for knee osteoarthritis: a randomized clinical trial. JAMA 2024 (PMID 38776073)
- NHS: Warfarin
Educational information for people in the United Kingdom — not personal medical or dietary advice. Food and supplements can interact with medicines, so check with your GP, pharmacist or rheumatology team before changing your diet significantly or starting a supplement, and ask for a referral to a registered dietitian for individual advice. Charity no. 1218461. Pending clinical and editorial review. If you feel very unwell, call 999 or go to A&E. For urgent advice, contact NHS 111.
Continue with related help
- Oily fish and arthritis — food-first ideas
- Simple oily fish meals — easy recipes
- Medicine and supplement interactions — full safety guide
- Anti-inflammatory diet — the overall eating pattern
- Supplements hub — all our supplement guides