Fish Oil Side Effects and Safety: What You Should Know

Fish oil comes from the tissue of oily fish like salmon, mackerel, and sardines.

It contains two main omega-3 fatty acids, EPA and DHA.

These fats play a role in heart, brain, and eye health.

People take fish oil as a supplement when they do not eat enough fatty fish.

It comes as liquid, capsules, or gummies, and doses vary widely between products.

Omega-3s from fish oil have been studied for many parts of health.

Research links fish oil to support for heart health, including effects on blood pressure and triglycerides.^[2]

Some studies suggest fish oil may ease symptoms of depression, though results are mixed.^[3]

Older research also looked at fish oil for blood pressure control in people with hypertension.^[4]

Some evidence points to a possible role for omega-3s in easing inflammation linked to conditions like endometriosis.^[1]

Newer research has even tested fish oil alongside standard acne treatment.^[7]

Most side effects from fish oil are mild and involve the stomach.

• Fishy aftertaste or burps
• Bad breath
• Heartburn or indigestion
• Nausea
• Loose stools or diarrhea
• A fishy smell to sweat

These effects tend to happen more with high doses or low-quality oil that has started to go rancid.

Taking fish oil with meals can lower stomach upset.

Freezing capsules can also reduce burping, since it delays the oil from breaking down until it reaches the small intestine.

Omega-3 fatty acids can affect how blood clots.

They influence compounds called prostaglandins, which are made by enzymes known as cyclooxygenases, or COX enzymes.^[6]

These enzymes help control clotting and inflammation throughout the body.^[6]

At high doses, fish oil may thin the blood enough to raise the risk of bruising or bleeding.

This risk goes up in people who also take blood thinners, such as warfarin or aspirin.

People scheduled for surgery are often told to stop fish oil beforehand for this reason.

Anyone on blood thinners or with a bleeding disorder should check with a doctor before taking fish oil.

Fish oil is often linked to calmer, less inflamed skin, but the picture is more complex.

One lab study found that fish oil changed how a skin treatment called imiquimod was absorbed and how much inflammation it triggered.^[5]

This suggests fish oil can change how the skin responds to other topical treatments, not just calm it down.^[5]

A recent clinical trial tested fish oil alongside isotretinoin, a strong acne medication, in people with moderate to severe acne.^[7]

The combination was found to be safe and about as effective as isotretinoin alone, without adding new safety concerns.^[7]

This kind of research is a reminder that supplements can interact with medications in ways that are still being studied.

• People taking blood thinners or antiplatelet drugs
• People with a bleeding disorder
• People scheduled for surgery in the near future
• People with a known fish or shellfish allergy
• People taking blood pressure medication, since fish oil can add to blood pressure lowering effects^[4]
• Pregnant people, who should choose a purified, low-mercury product and check with a doctor first

People with any chronic health condition should also loop in a doctor before adding a new supplement.

For most healthy adults, fish oil at normal doses appears safe for the heart.^[2]

Omega-3s have long been studied for their role in triglyceride levels and heart rhythm.^[2]

Still, very high doses have been tied in some research to a higher risk of an irregular heartbeat called atrial fibrillation.

This is one more reason to stick to reasonable doses rather than assuming more is better.

Anyone with existing heart disease should talk to a doctor about the right dose for them.^[2]

Health authorities generally consider up to about 3 grams of combined EPA and DHA per day safe for most adults.

Doses used in research for specific health goals sometimes go higher, but only under medical supervision.^[3]

Going well beyond this range raises the odds of side effects like bleeding and stomach upset without clear added benefit.

Checking the label for actual EPA and DHA content matters more than the total fish oil amount, since concentrations vary widely between products.

• Start with a lower dose and see how your body responds
• Take fish oil with a meal to reduce stomach upset
• Store capsules in the fridge or freezer to cut down on fishy burps
• Choose a product that has been tested by a third party for purity
• Check the EPA and DHA amounts on the label, not just the total fish oil dose
• Tell your doctor about any fish oil use before surgery
• Ask a doctor before combining fish oil with blood thinners or blood pressure medication
• Stop use and seek medical advice if you notice unusual bruising or bleeding

Getting omega-3s from food, like salmon, sardines, or walnuts, is another way to support intake without relying only on supplements.