Fish oil supplements provide many health benefits, boosting the brain, improving heart health, reducing inflammation, and more. However, as is the case with any medication or supplement you're considering taking, it's important to weigh all of the risks and benefits with the help of your doctor before beginning a new regimen.
"There's no doubt that fish oil provides omega-3 fatty acids, which offer important health benefits—but like any supplement, fish oil does come with some potential risks," says Farhan Malik, MD, a double board-certified doctor in family medicine and sports medicine, and the owner and senior medical director at Prometheus by Dr. Malik.
He notes that problems are most likely to occur when you take too high of a dose. "More is not always better when it comes to supplements," Malik tells Best Life. "Always be cautious about dosage and freshness when taking fish oil. Moderation and paying attention to quality is key."
Wondering what hidden dangers may be lurking behind fish oil's stellar reputation? Read on to learn the seven side effects you should consider before you start taking the supplement.
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1 | They can interfere with blood clotting.
iStockFish oil supplements have been shown to reduce platelet aggregation in individuals without circulatory problems, and recent studies have investigated whether they should be stopped prior to surgery due to increased bleeding risk, says Jennie Stanford, MD, FAAFP, DipABOM, a double board-certified physician specializing in family medicine and obesity medicine. However, she says evidence indicates there is no increased bleeding risk and no indication to stop fish oil supplements before surgery.
That said, Malik reports having seen clotting issues in his own practice and notes that the key to avoiding them is to stick to the recommended dosage on the supplement label.
"Excessive amounts of fish oil can actually lead to bleeding problems," he says. "I've seen patients experience nosebleeds or bruising more easily from taking very high doses of fish oil for long periods."
2 | They can cause gastrointestinal upset.
ShutterstockIf you have a sensitive gastrointestinal system, taking fish oil supplements may cause GI upset, says Stanford, who is also a medical contributor for Drugwatch.
"In some people, fish oil supplements may cause nausea, diarrhea, bloating, or belching with a fishy aftertaste," Stanford tells Best Life. "These effects are generally mild, and they occur less frequently when taking a coated fish oil tablet or capsule. Taking fish oil supplements with a meal also reduces these side effects."
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3 | They can affect glycemic control.
Proxima Studio / ShutterstockDepending on your health, taking high doses of fish oil can have either beneficial or adverse effects on blood sugar regulation.
"Fish oil supplementation is known to improve lipid metabolism in patients with dyslipidemia," says Stanford, referring to a condition in which abnormal levels of lipids enter the bloodstream. "Another advantage of fish oil supplementation is that it may improve fasting blood glucose and insulin sensitivity, as impaired fasting glucose and insulin resistance commonly occur with dyslipidemia."
However, while this improvement in glycemic control is advantageous for many people, it may change the effects of glucose-lowering medications. "This makes it necessary to monitor blood glucose closely for hypoglycemia and to adjust medication doses accordingly," Stanford notes.
4 | They can cause interactions with other medications.
iStockAnother hidden danger associated with taking fish oil supplements is that, like most other supplements, they can interact with certain medications.
"Because fish oil supplementation has been shown to reduce blood clotting, it can interact with blood thinning and antiplatelet medications. With medications like aspirin, clopidogrel (Plavix), warfarin (Coumadin), and other anticoagulant medications, adding fish oil supplementation can increase the blood-thinning effect and elevate the risk of adverse bleeding," cautions Stanford.
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5 | In some people, they may increase stroke risk.
iStockThere's also contradictory research on the risks and benefits of fish oil supplements as they relate to atrial fibrillation and stroke risk.
"Many studies suggest that taking fish oil supplements may increase the risk that healthy individuals develop atrial fibrillation and then subsequent stroke," says Stanford. "However, in people with cardiovascular disease and predispositions to dysrhythmias (like atrial fibrillation), taking fish oil supplements appears to lower the risk of developing atrial fibrillation and subsequent stroke."
6 | They're prone to rancidity and oxidation.
iStockMalik notes that fish oil capsules can go rancid over time, especially if they aren't stored properly.
"Rancid fish oil loses its health benefits and may even contain compounds that are harmful. I advise my patients to store fish oil supplements in the refrigerator and be aware of expiration dates to avoid taking rancid pills. Smelling fish oil capsules before swallowing them is also a good way to check for freshness," he tells Best Life.
The doctor also cautions that fish oil supplements can be highly prone to oxidation, which can negate their benefits and even produce harmful byproducts.
"Many fish oil supplements end up oxidized before you even consume them. Oxidized oils are linked to increased oxidative stress and inflammation. For this reason, I only recommend pharmaceutical-grade fish oil brands that use proper processing and encapsulation methods to prevent oxidation," he says.
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7 | They can be contaminated.
shurkin_son / ShutterstockFinally, many people take fish oil supplements rather than eating fish in an effort to avoid consuming high levels of mercury, as well as other toxins or contaminants. However, Malik notes that recent research suggests there's still a risk of contamination when you take fish oil in supplement form.
"Fish can accumulate heavy metals like mercury and other toxins from polluted waters. If the oil is not purified and decontaminated properly, these contaminants can be concentrated in supplements. Consuming contaminated fish oil over long periods may have neurological and developmental effects. I advise choosing reputable brands that follow rigorous quality control measures," Malik says.
