Fish oil supplements deliver two omega-3 fatty acids, EPA and DHA, that most people don’t get enough of through diet alone. These fats play direct roles in heart health, joint comfort, brain structure, and inflammation control. The strongest evidence supports their use for lowering triglycerides, easing inflammatory joint pain, and supporting fetal brain development during pregnancy.
Lowering Triglycerides
The most well-established reason to take fish oil is to bring down triglycerides, a type of blood fat linked to heart disease. At therapeutic doses (around 4 grams per day of EPA and DHA), fish oil reduces triglycerides by roughly 20% to 30% in people with elevated levels. In people already taking statins, the reduction is closer to 21%, and in those not on other medications, it averages about 27%. One study in people who started with very low omega-3 blood levels saw a 48% drop.
Dose matters significantly. At 2 grams per day, triglyceride-lowering effects are roughly half as strong and sometimes no better than a placebo. The American Heart Association recommends 4 grams daily of prescription-strength omega-3s for people who need to manage high triglycerides, and about 1 gram daily of EPA plus DHA for people with existing coronary heart disease. The FDA caps dietary supplement labels at 2 grams per day, so higher therapeutic doses typically require a prescription product.
Reducing Inflammation
Omega-3 fatty acids compete with omega-6 fatty acids for the same enzymes in your body. Omega-6 fats produce signaling molecules that promote blood clotting and constrict blood vessels, while omega-3s produce versions that do the opposite: they inhibit abnormal platelet clumping and reduce clot formation. By shifting this balance, fish oil tips your body’s inflammatory response in a less aggressive direction.
Beyond this competition, omega-3s generate a class of compounds called specialized pro-resolving mediators. These molecules don’t just block inflammation; they actively help your body wind it down after an injury or infection. Your immune cells, particularly certain white blood cells, produce these compounds from EPA and DHA. Omega-3s also influence how immune cells communicate by changing the structure of cell membranes, which alters the way proteins cluster on the cell surface and dampens overactive immune signaling.
Joint Pain and Stiffness
For people with inflammatory joint conditions like rheumatoid arthritis, fish oil supplements taken for three to four months reduce self-reported joint pain, the number of painful or tender joints, and minutes of morning stiffness. A meta-analysis of clinical trials found that omega-3 supplementation also reduced participants’ use of anti-inflammatory painkillers, suggesting the relief was meaningful enough that people needed less medication. Joint swelling also improved compared to placebo. These effects are modest but consistent across studies, making fish oil a reasonable addition to, not a replacement for, standard joint care.
Brain Development During Pregnancy
DHA is a structural component of brain and retinal tissue, which is why prenatal omega-3 intake gets so much attention. Among eight randomized trials that gave pregnant women DHA supplements (ranging from 200 to 2,200 milligrams daily for about 20 weeks), five reported improvements in infant cognitive development scores of 6% to 11%. Every study, however, also reported at least one measure that didn’t reach statistical significance.
Evidence for other developmental outcomes, including language ability, motor skills, visual development, and risk of attention or behavioral disorders, remains inconsistent. So while there’s a reasonable case for DHA during pregnancy, the benefits appear specific to certain aspects of early cognitive development rather than being a broad boost to child neurodevelopment.
Brain Health in Older Adults
Higher omega-3 levels in the blood correlate with greater brain volume in regions that matter for memory and cognitive function. In a study of adults aged 65 and older, EPA levels and overall omega-3 status were positively associated with volume in the entorhinal cortex, a brain region that deteriorates early in Alzheimer’s disease. DHA was linked to greater white matter volume, which supports communication between brain regions. These are correlational findings, meaning they show an association rather than proving supplementation directly preserves brain tissue, but they align with the broader theory that omega-3s support structural brain health as you age.
Dry Eye Relief
Fish oil can improve dry eye symptoms by enhancing the oil layer of your tear film. This oil is produced by tiny glands along the edge of your eyelids, and when it’s insufficient, tears evaporate too quickly. Research has found that people taking omega-3 supplements report fewer dry eye symptoms and less need for artificial tears. The doses used in many of these studies were relatively modest: 180 milligrams of EPA and 120 milligrams of DHA, taken twice daily.
Side Effects and Risks
At standard doses, fish oil is generally safe. The most common complaints are a fishy aftertaste, bad breath, and digestive issues like heartburn, nausea, or diarrhea. Taking supplements with meals or freezing the capsules before swallowing can reduce these effects.
The more important concern is bleeding risk. Omega-3s reduce platelet activation, which is part of how they protect the cardiovascular system, but at high doses this same effect can increase the chance of bleeding. If you take blood thinners or antiplatelet medications, combining them with fish oil could amplify that risk. High doses may also slightly increase the risk of stroke in some people.
Choosing a Quality Supplement
Not all fish oil supplements are created equal. Oxidized (rancid) fish oil can be ineffective or even harmful, and some products contain less EPA and DHA than their labels claim. Third-party certification programs like the International Fish Oil Standards (IFOS) test supplements for three things: whether the omega-3 content matches the label, whether contaminant levels (heavy metals, PCBs) fall within safe limits, and whether the oil is fresh rather than oxidized. Looking for a certified product or checking batch-specific test results is the most reliable way to verify quality, since you can’t always tell from the label alone.
When reading a supplement label, focus on the combined EPA and DHA content per serving rather than the total “fish oil” amount. A capsule containing 1,000 milligrams of fish oil might deliver only 300 milligrams of actual EPA and DHA. The rest is other fats that don’t carry the same benefits.