CR tested fish oil supplements from brands such as CVS, GNC, Nordic Naturals, and The Diet Shoppe for heavy metals and rancidity, as well as to verify their label claims.
Some of the fish oil pills we tested showed signs of rancidity; Others contained less omega-3 fatty acids than their labels indicated.
By Catherine Roberts
Americans love fish oil supplements. They are among the five most popular supplements in the United States, according to a nationally representative CR survey of 2,272 American adults in February 2026, in which about one in five Americans reported taking fish oil in the past 12 months.
The promise of the pills is that they allow you to easily obtain a daily dose of omega-3 fatty acids, substances found in fatty fish such as salmon that perform a variety of important functions in the body and are associated with a lower risk of cardiovascular problems.
The reality is that these supplements probably only offer minimal health benefits, and only for people with certain health problems. For most people, fish oil pills will not significantly reduce the risk of heart attacks and strokes, according to the results of major clinical trials that compared the results of thousands of people who were given a supplement or a placebo.
What’s more, these pills can cost more than $30 a month, and several studies over the years have raised concerns that they could expose consumers to harmful chemicals, such as polychlorinated biphenyls (PCBs); pollutants that persist in the environment and can potentially cause cancer and other health problems.
To find out more about what Americans are really getting in each pill, CR analyzed 20 popular fish oil supplements. 16 of them met all of our safety and quality standards. However, while our testing revealed that most of the products tested did not have concerning levels of any of the contaminants we checked, one product did not meet its label claims, and others contained oil that may have gone rancid.
Here’s what you need to know about our latest fish oil pill tests, as well as what these supplements can (and can’t) do for your health.
Contaminants in fish oil
Due to water pollution, fish can accumulate various toxic contaminants. These include dioxins and PCBs, as well as heavy metals such as lead and mercury. This is, in part, why CR has periodically reviewed fish oil capsules over the years; to check whether toxic contaminants sometimes found in fish are also finding their way into fish oil supplements, says CR food safety researcher Tunde Akinleye.
There is another fundamental concern with fish oil: rancidity. The unsaturated fatty acids present in fish oil, including the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), react easily with oxygen, a process known as oxidation. This can cause rancidity, the same phenomenon that can occur with expired fatty foods, such as cooking oils and nuts.
Previous research has detected signs of oxidation in fish oil capsules; However, it can be difficult to determine when a capsule (or even an entire bottle) has gone rancid.
It’s not entirely clear what exactly consuming rancid fish oil means for your health. Oil in this state tastes unpleasant, according to Tod Cooperman, president and founder of ConsumerLab.com, which regularly tests various supplements for contaminants, including fish oil pills. Additionally, there is what Cooperman calls the “burp factor.” Burping is a common side effect of omega-3 supplements, and when they are rancid, the experience can be much more unpleasant. Likewise, consuming any type of rancid oil could potentially cause some uncomfortable digestive symptoms.
What CR tests revealed
For our latest omega-3 supplement tests, we selected 20 popular fish oil pills and analyzed them for dioxins, PCBs, chlorinated paraffins, arsenic, cadmium, lead, and mercury. We also checked whether EPA and DHA levels matched each product’s label claims, and analyzed their oxidation levels. We also checked that each product met USP standards for how long it takes for supplements to break down in the body (the United States Pharmacopeia, or USP, is an independent organization that sets widely accepted standards for supplements). We analyze two or three samples of each brand, coming from at least two different batches. We conducted our tests between January and May 2025 with products purchased in the fall of 2024; These analyzes represent a snapshot of that specific moment.
The good news: 16 of the brands met all of our quality and safety standards. Additionally, some aspects of fish oil safety have improved since we last reviewed these supplements in 2012; On that occasion, four tested positive in at least one sample for PCB levels that exceeded our threshold of concern, which is based on California’s Proposition 65. On this occasion, no brand exceeded these levels.
However, we also found some worrying results in some key areas.
Rancidity. Three of the products we analyzed had oxidation levels that exceeded the total oxidation limit established by the World Group for EPA and DHA Omega-3s (GOED), an industry representative group. According to Akinleye, this oxidation is an indication that these are lower quality products that could be rancid. (None of these products had expired at the time of testing.)
In several cases, we were unable to draw definitive conclusions about the oxidation levels of certain products, since they contain lemon oil and other specific flavorings that may interfere with oxidation tests. There is currently no alternative to these oxidation tests; Therefore, we cannot state with certainty whether these supplements showed signs of rancidity. However, they met all of CR’s other quality and safety tests, so our experts still consider them high-quality products.
Label claims for EPA and DHA. To meet our minimum quality standard for label claims, products had to contain at least 90% of the amount of EPA and DHA indicated on the label. One product did not meet this level: our samples of Qunol Extremely Omega-3 Mini Softgels 1000 mg averaged only 83% of the amount of EPA declared on the label, and only 85% of the declared amount of total omega-3 fatty acids.
Minimal amounts of heavy metals and contaminants. All of the supplements we tested met our standards for the contaminants tested. These standards are based on levels established by various public health agencies, including California Proposition 65 levels for lead and total PCBs, the European Food Safety Authority limits for dioxins and paraffins, and the Environmental Protection Agency limits for methylmercury. (For more information about our testing methods and standards, see our detailed methodology.)
Even so, we detected small amounts of some contaminants. Nearly half of the supplements we tested contained small amounts of lead, and all had traces of dioxins and PCBs. However, all of these levels were below the strict benchmarks we used for our assessments.
Supplement companies respond
We contacted manufacturers whose products either did not contain the amount of EPA and DHA claimed on their labels, or exceeded the CR standard for oxidation, indicating possible rancidity. We request information about your testing and quality adjustment procedures, as well as any comments regarding our findings.
In our testing, we found that Qunol supplements contained only 83% of the EPA and 85% of the total omega-3s claimed on the label. The company disputed our findings, arguing that the test we used is not suitable for assessing omega-3 levels, since the presence of lemon oil can interfere with it. However, while lemon oil flavoring can affect oxidation level test results, CR experts are not aware of any evidence indicating that flavoring oils can affect test results for omega-3 fatty acid content. We asked Qunol to provide such evidence, but received no response from the company.
We also contacted companies whose supplements showed signs of rancidity. One of them was Costco (Kirkland), which did not respond to our messages.
Nature Made did respond, stating that their own testing, conducted on the same lot numbers CR tested, revealed that their supplements met our standards for oxidation indicators.
California Gold Diet also responded and told us that it had temporarily suspended sales of the lot numbers we tested for its Youngsters Omega-3 Fish Oil Softgels. The company informed us that it is reviewing its original test data for these batches and is retesting some samples.
The evidence on fish oil supplements
Years of nutrition research have shown that diets rich in omega-3 fatty acids appear to be more beneficial for people’s cardiovascular health than those with low levels of these substances, according to Dr. Donald Lloyd-Jones, principal investigator of the Framingham Coronary Heart Study at Boston University School of Medicine and scientific leader of clinical research services at the American Heart Association. Other studies have also found that people with higher levels of EPA and DHA in their blood tend to have a lower risk of heart attacks, coronary heart disease, and other problems.
So it’s no surprise that people are turning to supplements with EPA and DHA in an effort to improve their heart health.
And omega-3s play crucial roles in the body. For example, they help shape the structure of cell membranes; Additionally, the body uses them to form molecules that fulfill a wide range of functions in the cardiovascular system, immune system, and other areas. However, while overall consumption of fatty fish, other than fried, has been consistently associated with a lower risk of cardiac mortality, coronary heart disease, and stroke, the evidence is less conclusive regarding the benefits of obtaining omega-3s exclusively through supplements. These pills may not actually be beneficial for the general population, research suggests, although some people may benefit from them. Those with certain pre-existing cardiovascular problems could obtain some benefit.
An independent analysis of 86 randomized controlled trials, published in 2020, found that people who took a fish oil supplement did not have a lower risk of having a stroke or dying from cardiovascular disease, compared to those who took a placebo pill or followed their normal diet. The researchers did find that people who took fish oil pills may have a lower chance of having a heart attack; However, the difference was so slight that the authors noted that it could not be conclusively attributed to fish oil. The authors wrote that omega-3 supplements “are probably not useful in preventing or treating cardiovascular disease.”
Lloyd-Jones agrees with this position. Regarding the general population, he states: “We have not observed that supplementation with omega-3 fatty acids reduces the risk of cardiovascular diseases.”
Lloyd-Jones notes that while earlier clinical trials of fish oil pills showed a more significant benefit for people with pre-existing cardiovascular disease, more recent trials have not revealed the same advantages. This could be, in part, because statins and other risk-reducing medications are now routinely used in patients who have had a previous heart attack or other coronary events, he says. Such a circumstance would make it difficult to detect the much more tenuous effects that supplements might have.
Plus, there’s a potential downside: Some evidence suggests that, in healthy people, regular use of omega-3 supplements may increase the risk of certain cardiovascular problems, such as atrial fibrillation and stroke.
Who should consider taking fish oil supplements?
Some groups of people may gain certain benefits from fish oil supplementation, although the strength of the evidence varies between different groups.
People with very high levels of triglycerides. Some of the strongest evidence for the benefits of fish oil relates to lowering triglycerides. For people who already have cardiovascular disease and have very high triglyceride levels (greater than 500 mg/dL, according to Lloyd-Jones), omega-3 supplementation appears to be beneficial. However, the main objective in these cases is to reduce the risk of pancreatitis associated with such high triglyceride levels, explains Lloyd-Jones. In these situations, he says, it is essential to use a prescription fish oil supplement (something we will discuss later).
People with pre-existing heart diseases. The American Heart Association’s recommendation for fish oil supplements reflects the little potential benefit for people who already have heart problems. The organization emphasizes eating more fatty fish as the best source of omega-3s, but also recognizes supplements as a reasonable option for risk reduction in people with pre-existing heart disease (particularly because they carry a low risk of side effects).
People with end-stage kidney disease who receive maintenance dialysis. In a recent randomized controlled trial published in the Unusual England Journal of Medication, researchers gave daily fish oil or placebo pills to 1,228 people undergoing dialysis treatments for end-stage kidney disease. Those who received the fish oil supplements experienced a lower rate of serious cardiovascular events, including heart attacks, strokes and death.
People with inflammatory conditions. There is also some evidence that omega-3 supplements may have some anti-inflammatory effects that may be helpful for people with rheumatoid arthritis and other inflammatory conditions, such as lupus or multiple sclerosis.
What consumers should do
Bask in fish abundantly. The American Heart Association recommends eating two servings of fish a week, especially fatty fish such as salmon, anchovies, herring, mackerel, sardines, bluefin tuna, oysters and mussels. This is by far the best way to get enough omega-3 fatty acids in your diet.
Choose higher quality supplements. If you decide to take over-the-counter fish oil supplements, CR food safety experts recommend choosing products that meet all of our quality and safety standards. This will give you a greater chance of purchasing a product that is not rancid and that contains the amount of omega-3 declared on its label.
Extend the life of your supplements. Store fish oil supplements in a cool, dry cupboard, away from direct sunlight.
Consider prescription supplements for medical needs. If you plan to take fish oil for a specific medical reason, such as high triglycerides, ask your doctor about prescription supplements. Prescription medications must meet stricter quality and safety requirements than supplements.
You can probably do without giving fish oil supplements to children. Fish oil pills are widely marketed, both to adults (beyond the groups with pre-existing conditions mentioned above) and children. Two of the products we reviewed are specifically aimed at children. Legally, supplements cannot claim to treat any specific condition; Therefore, the claims on the labels of these products are deliberately vague. For example, Nordic Naturals claims that its Youngsters’s DHA supplement “supports brain development.” Several studies have investigated the use of omega-3 supplements to treat a variety of conditions, including attention-deficit/hyperactivity disorder (ADHD), asthma, and allergies. However, the available evidence is, to date, inconclusive. For example, some analyzes pooling results from randomized controlled trials have suggested that omega-3 supplements may help relieve ADHD symptoms in children, while others have concluded that they had no effect on ADHD symptoms. What’s more, these pills are not mentioned at all in the American Academy of Pediatrics’ comprehensive clinical guidelines on the treatment of childhood ADHD.
In general, if you are looking to improve your heart health, making adjustments to your habits, such as eating a balanced diet and reducing a sedentary lifestyle, will probably be more beneficial than taking omega-3 supplements. As Lloyd-Jones states: “It is an act of arrogance to believe that we can reduce a healthy eating pattern to a simple pill.”
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