What fish oil supplements contain and why people use them
Fish oil supplements are capsules or liquids made from the fat of fatty fish like salmon, mackerel, and sardines. They contain two types of omega-3 fatty acids: EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Your body cannot make these on its own, so they come only from food or supplements.
People take fish oil because omega-3s play a role in how your heart, brain, and joints work. Your cell membranes, the protective layers around every cell, are partly made of these fats. Some research suggests that getting enough omega-3s may support heart health, reduce inflammation in the body, and help with brain function as you age. The amount of research backing each of these claims varies—some are stronger than others.
Fish oil is one of the most commonly taken supplements in the United States. People choose it for different reasons: some eat little fish and want to fill that gap, others have been told by a doctor that omega-3s might help with a specific health concern, and some straightforward want to support their overall health.
Key Takeaways
- Fish oil supplements contain EPA and DHA, two omega-3 fatty acids that your body needs but cannot produce on its own.
- Research shows the strongest evidence for fish oil's role in heart health, particularly for people with high triglycerides or existing heart disease.
- Most people can get omega-3s from eating fish two to three times per week, which may be as effective as taking a supplement.
- Fish oil supplements can interact with blood-thinning medications and may cause side effects like fishy aftertaste, nausea, or loose stools.
- Talking with your doctor before starting fish oil is important if you take medications, have a bleeding disorder, or are pregnant.
What the research shows about fish oil and heart health
The strongest evidence for fish oil comes from studies on heart health. Research has found that omega-3s can lower triglycerides (a type of fat in your blood) and may help reduce blood pressure slightly. For people who have already had a heart attack or have been diagnosed with heart disease, some studies suggest that fish oil may lower the risk of another cardiac event.
The picture is less clear for people without existing heart disease who take fish oil to prevent problems. Some large studies found that fish oil did not prevent heart attacks or strokes in people with no history of heart disease, while other research suggested modest benefits. This is why doctors do not routinely recommend fish oil for prevention in people with no symptoms or risk factors.
If you have high triglycerides or heart disease, your doctor may recommend fish oil as part of your treatment plan. The dose matters—studies showing benefits often used higher amounts than you find in a standard multivitamin.
Other health areas where people use fish oil
Beyond heart health, people take fish oil for joint health, brain function, and inflammation. Some research suggests omega-3s may help reduce joint pain and stiffness in people with rheumatoid arthritis, though the effect is usually modest. For brain health, studies have looked at whether fish oil slows cognitive decline as people age, but results have been mixed—some show a small benefit, others show none.
Fish oil is also used for dry eyes, mood support, and skin health, but the evidence for these uses is thinner. If you are considering fish oil for any of these reasons, it is worth discussing with your doctor what the current research actually shows and whether it makes sense for your situation.
It is important to understand that taking a supplement is not the same as treating a diagnosed condition. Fish oil may support your health, but it is not a replacement for medications or other treatments your doctor has prescribed.
How much fish oil you might need and where it comes from
There is no single official recommended amount for omega-3s the way there is for vitamins like C or D. Different organizations suggest different targets. The American Heart Association recommends eating fatty fish twice per week, which gives you about 250 to 500 milligrams of EPA and DHA combined per day. If you take a supplement, doses typically range from 1,000 to 3,000 milligrams per day, depending on what you are using it for.
Fish oil supplements come from wild-caught fish, farmed fish, or both. Some supplements are molecularly distilled to remove contaminants like mercury and PCBs (industrial chemicals that can accumulate in fish). If you are concerned about contaminants, look for third-party testing labels on the bottle—organizations like NSF International and USP test supplements and verify what is actually in them.
Algae-based omega-3 supplements are also available and may be a choice if you do not eat fish or prefer a plant-based option. These contain DHA and EPA that come from algae rather than fish.
Side effects and who should be cautious
Fish oil supplements are generally well tolerated, but some people experience side effects. The most common are a fishy aftertaste, nausea, loose stools, and stomach upset. Taking fish oil with food often reduces these effects. Some people also report burping or heartburn.
Fish oil can thin the blood slightly, which matters if you take blood-thinning medications like warfarin or aspirin. If you are on any blood thinner, talk with your doctor before starting fish oil—you may need to adjust your dose or monitor more closely. People with bleeding disorders should also check with their doctor first.
Pregnant and breastfeeding people should discuss fish oil with their doctor before taking it. While omega-3s are important for fetal brain development, the dose and source matter. Some fish contain mercury, which is why pregnant people are advised to eat certain types of fish in limited amounts. A supplement can be a safer way to get omega-3s during pregnancy, but your doctor should guide the choice.
Fish oil versus eating fish: which is better
Eating fatty fish two to three times per week gives you omega-3s plus protein, vitamin D, selenium, and other nutrients that fish contains. A supplement gives you omega-3s alone. For most people, eating fish is considered the better first choice because you get more nutritional benefit overall.
Supplements make sense if you do not eat fish, are allergic to fish, follow a vegetarian or vegan diet (in which case algae-based supplements work), or your doctor has recommended a specific dose for a health reason. Some people do both—they eat fish regularly and take a supplement on days they do not eat fish.
Cost is also a factor. A bottle of fish oil supplements typically costs $10 to $30 per month, while eating fish can be more or less expensive depending on what you buy and where you live. Canned fish like sardines and mackerel are often cheaper than fresh salmon.
How to choose a fish oil supplement if you decide to take one
If you and your doctor decide fish oil makes sense for you, here is what to look for. Check the label for the amount of EPA and DHA—this is what actually matters, not the total fish oil amount. A supplement might say "1,000 mg fish oil" but contain only 300 mg of EPA and DHA combined. Read the label carefully.
Look for third-party testing seals from NSF International, USP, or ConsumerLab. These organizations test supplements to verify that what is on the label is actually in the bottle and that contaminants are within safe limits. This is not required by law, but it is a sign that the manufacturer has done extra quality checks.
Store fish oil in a cool, dark place or in the refrigerator to prevent it from going rancid. Check the expiration date before you buy and use it before that date. If your supplement smells off or tastes unusually strong, it may have oxidized and should be replaced.
Frequently Asked Questions
Can I take fish oil every day?
Yes, most people can take fish oil daily without problems. The typical dose is 1,000 to 3,000 milligrams per day. Very high doses (above 3,000 mg daily) may increase bleeding risk, so if you are taking a high dose, your doctor should know. Daily use is safe for most people, but check with your doctor if you take blood thinners or have a bleeding disorder.
Will fish oil help me lose weight?
Fish oil is not a weight loss supplement. Some research has looked at whether omega-3s support weight management as part of a healthy diet and exercise routine, but the evidence is weak. Fish oil may help you feel full slightly longer, but it is not a replacement for diet and activity changes.
Is fish oil the same as cod liver oil?
No. Cod liver oil comes from the liver of cod fish and contains omega-3s plus vitamins A and D. Regular fish oil comes from the body fat of fatty fish and does not contain added vitamins. Cod liver oil can provide too much vitamin A if taken in high doses, so it is not recommended for pregnant people. Choose regular fish oil unless your doctor specifically recommends cod liver oil.
Can I take fish oil with other supplements or medications?
Fish oil can interact with blood thinners, NSAIDs (like ibuprofen), and some other medications. It may also interact with certain supplements like garlic or ginger, which also thin the blood. Always tell your doctor and pharmacist about any supplements you take, including fish oil, so they can check for interactions.
How long does it take to feel the effects of fish oil?
This depends on what you are taking it for. For heart health markers like triglycerides, changes usually show up in blood tests after four to eight weeks. For joint pain or other effects, some people notice changes within a few weeks, while others see no difference. If you do not notice a benefit after two to three months, talk with your doctor about whether to continue.