⚕️ Educational information only — not medical advice. Read the full disclaimer

Fish Oil & Omega-3 for Arthritis: What the Evidence Shows

Fish oil is the most studied supplement for inflammatory arthritis, and the biology behind it is genuinely interesting: the omega-3 fats EPA and DHA change which inflammatory messengers your cells make and feed the molecules that help switch inflammation off. The clinical results are more modest. In rheumatoid arthritis, trials over four decades point to a small benefit, possibly letting some people use fewer painkillers, but the most recent meta-analysis rates the evidence low to very low certainty. In osteoarthritis, high doses have not beaten low doses or placebo. This page goes deeper than our supplements overview: EPA/DHA versus plant omega-3, the mechanisms, the key trials, the doses studied, food versus capsules, the omega-6 question, safety (bleeding and atrial fibrillation), product quality and plant-based algal oil.

Important: This page is general educational information, not medical advice. Arthritis must be diagnosed and managed by a qualified clinician. Talk to your doctor or pharmacist before starting fish oil, especially at the higher doses used in arthritis trials or if you take blood thinners or have a heart-rhythm problem. Never stop or change a prescribed medication, including NSAIDs, DMARDs or anticoagulants, without speaking to the prescribing physician.

Key takeaways

  • The omega-3s tested in arthritis are EPA and DHA from fish, krill or algae. Plant ALA (flax, chia, walnuts) converts to EPA only to a limited degree and to DHA very poorly.1 Strong
  • In rheumatoid arthritis, an older meta-analysis found reduced NSAID use at more than 2.7 g/day for over 3 months, but a 2024 meta-analysis of 23 placebo-controlled trials found only small, uncertain effects and suggested the NSAID finding may reflect imperfect blinding.23 Emerging (small effect)
  • An Australian early-RA trial found high-dose fish oil (5.5 g/day EPA+DHA) added to triple DMARD therapy was linked to fewer treatment failures and more remissions; it has not been replicated.4 Emerging
  • In knee osteoarthritis, high-dose fish oil did no better than low-dose over 2 years, krill oil trials disagree, and the ACR guideline advises against fish oil for OA.567 Contested
  • In cardiovascular trials, omega-3 supplements were linked to a higher risk of atrial fibrillation, most clearly above 1 g/day.8 Overall bleeding risk was not raised, but check with a pharmacist if you take a blood thinner.9 Strong (safety signal)
  • Cutting omega-6 seed oils to "fix the ratio" has not been shown to help arthritis; raising EPA/DHA is the part that has actually been tested.1011 Contested

EPA, DHA and ALA: which omega-3? Strong

"Omega-3" covers several fats that behave quite differently in the body. The arthritis research is almost entirely about the two long-chain marine omega-3s:

The main omega-3 fatty acids
Fatty acidMain sourcesRelevance to arthritis research
EPA (eicosapentaenoic acid)Oily fish, fish oil, krill oil, some algal oilsCompetes with arachidonic acid; precursor of E-series resolvins. Present in nearly all arthritis trial products.12
DHA (docosahexaenoic acid)Oily fish, fish oil, algal oilPrecursor of D-series resolvins, protectins and maresins.13
ALA (alpha-linolenic acid)Flaxseed, chia, hemp, walnuts, canola and soybean oilsA plant "parent" omega-3. Conversion to EPA is limited, especially in men, and further conversion to DHA is very low; conversion is somewhat higher in women.1

The practical upshot: flaxseed and walnuts are healthy foods, but they are not a substitute for the EPA and DHA doses used in arthritis trials. If you avoid fish, algal oil is the direct plant-based source of preformed DHA (and, in some products, EPA); see below.

Mechanisms: eicosanoids and pro-resolving mediators Emerging (lab and animal)

Mechanism: how EPA and DHA damp down inflammation

Cell membranes hold a pool of the omega-6 fat arachidonic acid. When a cell is stimulated, enzymes (COX and LOX, the same ones NSAIDs block) turn it into eicosanoids such as prostaglandin E2 and leukotriene B4, which drive pain, swelling and the recruitment of white cells. Eating more EPA and DHA partly replaces arachidonic acid in those membranes, so fewer of these mediators are made, and the EPA-derived versions tend to be less potent. In laboratory and human studies, EPA and DHA also reduce leukocyte chemotaxis and adhesion, lower production of inflammatory cytokines, and dampen the NF-κB "master switch" for inflammatory genes.12

The second story is resolution. EPA and DHA are precursors of specialized pro-resolving mediators (SPMs), the resolvins, protectins and maresins, which actively help end an inflammatory response and clear debris rather than simply blocking it. Synthetic SPMs have potent effects in animal experiments, including on pain and tissue protection.13

How much of this happens in a human joint at supplement doses is still uncertain. Most of the SPM work is from cell and animal models, and changes in eicosanoids or SPMs in blood do not automatically mean fewer swollen joints. The mechanism explains why fish oil is plausible; the trials below show how much it actually helps. For the bigger picture on inflammation, see our anti-inflammatory diet page.

Evidence in rheumatoid arthritis Emerging (small effect)

Fish oil has been tested in RA since the 1980s, mostly as an add-on to usual care. Pooled results have become less encouraging as more and better trials have been added:

Meta-analyses of omega-3 supplements in rheumatoid arthritis
ReviewTrials includedMain findingCaveats
Lee et al., 2012210 RCTs (183 treated, 187 controls); ≥2.7 g/day for ≥3 monthsClear reduction in NSAID use (SMD −0.52); non-significant trends for tender and swollen joints, morning stiffness and functionSmall trials; NSAID use is partly a patient choice and sensitive to unblinding
Senftleber et al., 20171442 trials of marine oils in arthritis; 22 in RA reported painSmall pain reduction overall (SMD −0.24) and in RA (SMD −0.21); none detected in OAOverall evidence low quality; moderate quality in RA
Gkiouras et al., 2024323 placebo-controlled RCTsSmall effects on pain (SMD −0.16), tender joints (−0.20) and swollen joints (−0.10), all with confidence intervals crossing zero; CRP down only 0.21 mg/dLCertainty mostly low or very low; earlier NSAID-reduction findings "may have been biased" by inadequate blinding

How to read this: the direction of effect is consistently favorable, but the size is small, smaller than that of established RA drugs, and the newest analysis cannot rule out no effect. That is why our supplements guide and RA page grade fish oil as Emerging for RA. A reasonable framing is "a low-risk add-on that may help some people a little", not a disease-modifying treatment.

Fish oil does not replace DMARDs. In RA, uncontrolled inflammation can damage joints within months, and early disease-modifying treatment is what prevents that. No fish oil trial has shown it can substitute for methotrexate or other DMARDs. Discuss any supplement with your rheumatologist as a possible addition.

The NSAID-sparing question Emerging

The most-repeated claim for fish oil in RA is that it lets people take fewer anti-inflammatory painkillers (NSAIDs). The evidence:

  • Kremer et al., 1995: 66 people with RA taking diclofenac received high-dose fish oil (130 mg/kg/day of omega-3s) or corn oil. When diclofenac was swapped for a placebo, tender joint counts in the fish oil group stayed significantly lower than at baseline and than in the corn oil group, and the authors reported that some patients could stop NSAIDs without a flare.15
  • Lee et al., 2012 meta-analysis: NSAID consumption fell significantly (SMD −0.52, no heterogeneity) at more than 2.7 g/day for over 3 months.2
  • Gkiouras et al., 2024 meta-analysis: in sensitivity analyses the reduction in NSAID intake was small and uncertain (SMD −0.22, 95% CI −0.90 to 0.46), and the authors suggested earlier positive findings may have been biased by inadequate blinding.3 Fish oil capsules can cause fishy burps, so participants may guess which group they are in.

What it supports

  • Under supervision, some people with RA may need less NSAID pain relief while taking high-dose fish oil.152
  • A reasonable topic to raise if NSAIDs upset your stomach or you want to use less of them.

What it does not show

  • That the effect is large, or that it survives fully blinded trials.3
  • That you should reduce or stop an NSAID, steroid or DMARD on your own. Any change should be planned with your doctor.

NSAIDs carry their own gastrointestinal, kidney and cardiovascular risks, discussed on our medications page; using less of them is a legitimate goal, but one to pursue with your prescriber.

The Australian early-RA trial (Proudman 2015) Emerging

The trial most often cited for fish oil in modern RA care came from Adelaide, Australia. People with RA of less than 12 months who had not yet taken DMARDs were randomized 2:1 to high-dose fish oil providing 5.5 g/day of EPA+DHA or a low dose of 0.4 g/day (used as a masking control). Everyone received triple DMARD therapy (methotrexate, sulfasalazine and hydroxychloroquine) adjusted to a treat-to-target algorithm.4

0.28Hazard ratio for failure of triple DMARD therapy with high-dose fish oil (lower is better)
2.17Hazard ratio for reaching first ACR remission (higher is better)
5.5 gDaily EPA+DHA in the high-dose group, vs 0.4 g in controls

Fish oil was associated with fewer triple-DMARD failures and a higher rate of ACR remission. However, there were no differences in methotrexate dose, DAS28 disease activity scores, function scores (mHAQ) or adverse events between the groups.4 It was a single research group's trial, it used a dose far higher than most people take on their own, and its findings have not been confirmed in a larger independent trial. It is encouraging evidence that fish oil can be a sensible add-on to DMARDs, not evidence that it can replace them.

Evidence in osteoarthritis Contested

Osteoarthritis has a smaller inflammatory component than RA, and the omega-3 results are correspondingly weaker:

Key omega-3 and krill oil trials in knee osteoarthritis
StudyDesignMain findingCaveats
Hill et al., 2016 (Annals of the Rheumatic Diseases)5202 people with knee OA; 15 mL/day of high-dose fish oil (4.5 g omega-3) vs low-dose (0.45 g, a fish oil and sunola oil blend), 2 yearsBoth groups improved; the low-dose group had greater improvement in WOMAC pain and function at 2 years. No difference in cartilage volume lossNo true placebo; the authors suggested the comparator oil itself needs study
Stonehouse et al., 202216235 adults with mild to moderate knee OA; 4 g/day krill oil (0.60 g EPA, 0.28 g DHA, plus astaxanthin) vs vegetable-oil placebo, 6 monthsModestly greater improvement in pain (−5.2 points on a 0–100 scale), stiffness and function; no difference in NSAID use or inflammatory markersSingle commercial product; modest effect size
Laslett et al., 2024 (JAMA)6262 people with knee OA, significant pain and MRI effusion-synovitis; 2 g/day krill oil vs placebo, 24 weeksNo difference in knee pain (between-group difference −0.3 on a 0–100 scale)Enrolled the inflammatory (effusion-synovitis) subgroup thought most likely to benefit
VITAL knee pain substudy, 2020171,398 older U.S. adults with chronic knee pain; 1 g/day omega-3 vs placebo, mean 5.3 yearsNo effect on WOMAC pain, function or stiffnessLow dose; chronic knee pain rather than confirmed OA in all participants

Pooled across trials, marine oils showed no significant pain benefit in OA (5 trials, SMD −0.17).14 The 2019 American College of Rheumatology/Arthritis Foundation guideline conditionally recommends against fish oil for hand, hip and knee OA.7 Exercise, weight management and education remain the foundation of OA care, as covered on our osteoarthritis page. Eating oily fish as part of a healthy diet is still reasonable for heart health; the case for high-dose capsules for OA pain is weak.

Can omega-3 prevent autoimmune disease? (VITAL) Contested

The VITAL trial randomized 25,871 U.S. adults aged 50 and over to vitamin D (2,000 IU/day), omega-3 (1 g/day) or placebos, in a two-by-two design, for a median of 5.3 years. Vitamin D reduced confirmed new autoimmune disease (including RA, polymyalgia rheumatica, autoimmune thyroid disease and psoriasis) by about 22%. In the omega-3 arm, 130 people on omega-3 and 148 on placebo developed an autoimmune disease, a 15% lower rate that was not statistically significant (hazard ratio 0.85, 95% CI 0.67 to 1.08).18

Observational data point the same way but cannot prove cause: in a Swedish cohort of 32,232 women, dietary long-chain omega-3 intake above 0.21 g/day was associated with a 35% lower risk of developing RA.19 People who eat more fish may differ in other ways, so this supports oily fish as part of a healthy pattern rather than supplements as a preventive drug.

Doses used in studies Emerging

The doses in positive RA trials are much higher than one or two standard capsules. The table shows what trials actually used so you can compare a label against the evidence; it is not a dosing recommendation.

Omega-3 doses studied in arthritis trials
StudyConditionDaily omega-3 doseDuration
Kremer 199515RA130 mg/kg/day omega-3s (roughly 9 g/day for a 70 kg adult)26–30 weeks
Lee 2012 (meta-analysis)2RA≥2.7 g/day EPA+DHA≥3 months
Proudman 20154Early RA5.5 g/day EPA+DHA (control 0.4 g/day)Assessed every 3 months
Adam 200320RAFish oil capsules at 30 mg/kg body weight, with or without a low-arachidonic-acid diet3-month crossover periods
Hill 20165Knee OA4.5 g/day vs 0.45 g/day omega-3 (liquid)2 years
Stonehouse 202216Knee OA4 g krill oil (0.88 g EPA+DHA)6 months
Laslett 20246Knee OA2 g krill oil24 weeks
VITAL1817Prevention; knee pain1 g/day omega-3~5 years
Points to discuss with your clinician: labels often show the total amount of fish oil on the front; what matters is the combined EPA+DHA per serving on the supplement facts panel. The European Food Safety Authority concluded that supplemental EPA+DHA up to about 5 g/day does not raise safety concerns for adults,21 but the atrial fibrillation signal discussed below rises with dose. RA trials typically ran for at least 3 months before benefits appeared, so a defined trial period with a symptom log (try our flare tracker) is a sensible way to judge whether it helps you.

Food vs. supplements Emerging

Oily fish

  • Provides EPA and DHA along with protein, vitamin D, selenium and other nutrients.
  • Fits a Mediterranean-style pattern, which has its own evidence in RA and clear cardiovascular benefits (see anti-inflammatory diet).
  • The FDA and EPA list salmon, sardines, anchovies, Atlantic mackerel and trout among the lowest-mercury "best choices".22
  • Reaching the 2.7–5.5 g/day of EPA+DHA used in RA trials from food alone would require far more oily fish than most people eat.

Capsules or liquid oil

  • The only practical way to reach trial doses.
  • Quality varies: oxidation and under-filled labels are common (see quality).
  • Purified fish oils contain little mercury.23
  • Higher doses bring the safety considerations below.
Mercury is a food issue, not mainly a supplement issue. The FDA and EPA advise avoiding the highest-mercury fish (king mackerel, marlin, orange roughy, shark, swordfish, Gulf of Mexico tilefish and bigeye tuna), particularly during pregnancy, breastfeeding and childhood.22

The omega-6 : omega-3 ratio Contested

A popular argument holds that modern diets carry too much omega-6 linoleic acid (from soybean, corn and other seed oils) relative to omega-3, and that "fixing the ratio" by cutting seed oils will calm joint inflammation. The biochemistry is real: arachidonic acid, an omega-6, is the precursor of pro-inflammatory eicosanoids.11 The human evidence for cutting linoleic acid is not:

  • A systematic review of 15 randomized trials in healthy adults found that adding linoleic acid did not raise CRP, cytokines or other inflammatory markers.10
  • No trial has tested seed-oil avoidance as an arthritis treatment. Our seed oils section covers this in more detail.
  • The fair caveat: high omega-6 intakes may blunt some of the effects of omega-3s, and the interaction is not fully understood.11

What has been tested in RA is a diet low in arachidonic acid itself, which comes mainly from meat, eggs and other animal foods rather than seed oils. In a small 8-month study of 68 patients, the low-arachidonic-acid diet reduced tender and swollen joints and enhanced the benefit of fish oil.20 The practical message: raising EPA and DHA is the part of the "ratio" with trial support. Whether you also lower omega-6 matters less than the overall quality of your diet.

Safety: bleeding, atrial fibrillation and more Strong

At ordinary doses fish oil is well tolerated. The common side effects are digestive: fishy aftertaste or burps, reflux, nausea and loose stools. The less common risks matter more at the higher doses used in arthritis trials.

Atrial fibrillation Strong (safety signal)

A 2021 meta-analysis in Circulation pooled 7 large cardiovascular trials with 81,210 participants followed for an average of about 5 years. Omega-3 supplements were associated with a 25% higher relative risk of atrial fibrillation (HR 1.25). The risk was greater in trials using more than 1 g/day (HR 1.49) than in those using 1 g/day or less (HR 1.12), and rose by about 11% for each additional gram.8

These were heart-disease trials, mostly in older adults, not arthritis trials. But the doses studied in RA (2.7–5.5 g/day) are above the range where the signal was strongest, so anyone with a history of atrial fibrillation, palpitations or other heart-rhythm problems should talk to their doctor before taking high-dose fish oil.

Bleeding and blood thinners Emerging

Omega-3s affect platelet function and clotting, which is why bleeding is a long-standing concern.24 A 2024 meta-analysis of 11 randomized trials with 120,643 patients found no overall increase in bleeding (rate ratio 1.09, not significant), including hemorrhagic stroke and gastrointestinal bleeding. High-dose purified EPA was associated with a 50% relative increase, though the absolute increase was small (0.6%).9 EFSA likewise concluded that supplemental EPA+DHA up to about 5 g/day does not appear to increase spontaneous bleeding.21

Reassuring as that is, these were mostly cardiovascular trials, and the stakes of a bleed on warfarin, a DOAC, clopidogrel, aspirin or regular NSAIDs are high. Ask your prescriber or pharmacist before starting fish oil if you take any of these, and tell your surgical team before an operation. Do not start, stop or change a blood thinner on your own.

Other considerations

Who should talk to a doctor or pharmacist before taking fish oil
If you…WhyEvidence
Have atrial fibrillation, palpitations or heart diseaseHigher AF risk in cardiovascular trials, especially above 1 g/day8Strong
Take warfarin, a DOAC, clopidogrel, aspirin or regular NSAIDsPossible additive bleeding risk; overall trial data are reassuring, but individual risk depends on your medicines9Emerging
Have surgery coming upSurgical teams often ask patients to pause supplements that affect platelets; follow their adviceEmerging
Have a fish or shellfish allergyFish oil is fish-derived and krill is a crustacean; ask an allergist, or consider algal oilEmerging
Have high LDL cholesterolEPA+DHA at 2–6 g/day can raise LDL by about 3%; EPA alone did not21Emerging
Are pregnant or breastfeedingOmega-3s are important in pregnancy, but high-dose supplements should be discussed with your maternity teamEmerging

Quality: oxidation, label accuracy and mercury Strong

Omega-3 fats are highly unsaturated, which makes them prone to going rancid (oxidizing). Independent testing has found widespread problems:

  • Of encapsulated fish oils tested in New Zealand, 83% exceeded recommended peroxide values and 50% exceeded total oxidation (TOTOX) limits; only 8% met all international recommendations. Most products (69%) contained less than two-thirds of the labeled EPA+DHA, and price, best-before date and country of origin were poor guides to quality.25
  • Whether oxidized oil is harmful in people is not settled, but it may be less effective, and EFSA's safety conclusion was conditional on the oxidative stability of the oil being guaranteed.21
  • Mercury is a small concern with purified fish oil: five U.S. over-the-counter brands tested had non-detectable to negligible mercury.23

Look for

  • Third-party testing (for example USP Verified, NSF, or an independent omega-3 quality program) for label accuracy, oxidation and contaminants.
  • The EPA and DHA content per serving clearly stated.
  • Storage as directed (cool, sealed, away from light); liquid oils refrigerated after opening.

Be wary of

  • A strong rancid or "off" smell when you break a capsule.
  • Claims to "cure arthritis", "rebuild cartilage" or "replace your medication".
  • Blends that hide EPA/DHA amounts, or very high doses taken without medical advice.

Our supplement quality guide covers third-party testing in more detail.

Plant-based options: algal oil Strong (DHA delivery) Contested (arthritis benefit)

Fish do not make most of their omega-3s; they accumulate them from the microalgae at the base of the food chain. Algal oil is made from cultured microalgae, so it is suitable for vegetarians, vegans and people who dislike fish. In a randomized study of 32 healthy adults, 600 mg/day of DHA from algal-oil capsules raised DHA in blood plasma (by about 80%) and red blood cells (by about 25%) just as effectively as the same DHA from cooked salmon.26

Two cautions. First, many algal oils are DHA-rich with relatively little EPA, while most arthritis trials used fish oils supplying both; check the label if you want EPA as well. Second, we are not aware of arthritis trials of algal oil specifically, so its joint effects are inferred from fish oil research. Flax, chia and walnuts supply ALA, which converts poorly to EPA and DHA.1

Dietary & supplement note: Statements here about foods and dietary supplements have not been evaluated by the U.S. Food and Drug Administration (FDA) and are not intended to diagnose, treat, cure, or prevent any disease.

When to see a doctor Strong

Seek prompt medical care if you:
  • notice a racing, fluttering or irregular heartbeat, chest pain, breathlessness or fainting;
  • have unusual bleeding or bruising, blood in urine or stool, or black stools, especially if you take a blood thinner;
  • have a hot, red, swollen joint with fever, which needs same-day assessment to rule out infection;
  • develop new joint swelling, morning stiffness lasting more than an hour, or several swollen joints, which can signal inflammatory arthritis needing early treatment.

Book a routine appointment or pharmacist review if you:

  • want to try fish oil at the higher doses used in RA trials;
  • take anticoagulants, antiplatelets or regular NSAIDs, or have a heart-rhythm condition;
  • hope to use less NSAID pain relief; plan any reduction with your doctor;
  • have taken fish oil for 3–4 months without clear benefit;
  • are considering fish oil in place of a prescribed treatment; please discuss this first rather than stopping anything on your own.

Frequently asked questions

Does fish oil help arthritis?

For rheumatoid arthritis, fish oil (omega-3 EPA and DHA) may give a small benefit as an add-on to usual treatment. Older trials and a 2012 meta-analysis suggested reduced NSAID use at more than 2.7 g/day, but a 2024 meta-analysis of 23 placebo-controlled trials found only small, uncertain effects on pain and joint counts, with low to very low certainty. For osteoarthritis, trials have been largely disappointing. Fish oil does not replace disease-modifying drugs. This is educational information, not medical advice.

How much fish oil is used in rheumatoid arthritis studies?

Trials reporting benefit in RA typically used at least 2.7 g per day of combined EPA and DHA for 3 months or more, and the Australian early-RA trial used 5.5 g per day. That is several times the EPA+DHA in one or two standard capsules. Check the EPA+DHA content on the label, not the total fish oil, and discuss any high dose with your doctor or pharmacist first.

Does fish oil help osteoarthritis?

The evidence is weak. In a 2-year Australian trial of 202 people with knee osteoarthritis, high-dose fish oil (4.5 g omega-3 a day) did no better than a low dose, and the low-dose group actually had greater pain improvement. Krill oil trials disagree, and the American College of Rheumatology guideline conditionally recommends against fish oil for osteoarthritis. Exercise and weight management remain the foundation of OA care.

Is fish oil safe with blood thinners?

Ask your prescriber or pharmacist first. A 2024 meta-analysis of 11 randomized trials found no overall increase in bleeding with omega-3s, although high-dose purified EPA raised bleeding risk slightly. Because bleeding on anticoagulants or antiplatelet drugs can be serious, do not start high-dose fish oil, or change a blood thinner, on your own, and tell your surgical team before any operation.

Can fish oil cause atrial fibrillation?

In large cardiovascular trials, omega-3 supplements were associated with a higher risk of atrial fibrillation: about 25% higher relative risk overall in a 2021 meta-analysis, and more at doses above 1 g a day. Arthritis trials use higher doses than that, so people with atrial fibrillation, palpitations or heart disease should talk to their doctor before taking high-dose fish oil. Seek care promptly for a racing or irregular heartbeat.

Is algal oil a good alternative to fish oil?

Algal oil, made from microalgae, is a vegetarian and vegan source of preformed DHA, and a randomized study found DHA from algal-oil capsules raised blood levels as well as cooked salmon. Many algal oils contain little EPA, and there are no dedicated arthritis trials of algal oil, so its effect on joints is inferred from fish oil studies. Flax, chia and walnuts provide ALA, which converts poorly to EPA and DHA.

References

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  3. Gkiouras K, Grammatikopoulou MG, Myrogiannis I, et al. Efficacy of n-3 fatty acid supplementation on rheumatoid arthritis' disease activity indicators: a systematic review and meta-analysis of randomized placebo-controlled trials. Crit Rev Food Sci Nutr. 2024;64(1):16–30. PubMed 35900212
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