Fish has many health benefits, but it can be hard to eat enough of the real thing to take advantage of them. Instead, many people choose to add fish oil supplements to their diet to lower their triglycerides, improve their heart health, and boost cognitive function.

While fish oil supplementation is generally safe, some people do experience side effects, which are usually mild. These side effects are more likely to occur when taking the supplement in high or very high doses.

If you experience any health issues, it is important to let your doctor know what supplements you take, including fish oil, as even safe supplements can interfere with medications or negatively impact underlying diseases.

Excessive Bleeding

One of the main reasons many people take fish oil is its heart-healthy benefits. A natural blood thinner, fish oil may help reduce the risk of blood vessel blockage and heart disease and lower triglyceride levels. However, in doing so, it may interfere with blood thinner medication and therefore increase the risk of bleeding.

This should not be a problem for most people, but those already taking prescription blood thinners should talk with their healthcare provider before adding fish oil to their diet.

fish oil concept with capsules and raw salmon


Digestive Symptoms

In rare cases, fish oil can cause digestive symptoms and affect your digestion, though this issue affects relatively few users. The gastrointestinal discomfort can range from a mild ache to persistent diarrhea.

There are a few ways to reduce the risk and severity of this side effect. Lowering the dosage may help, as may taking the fish oil at mealtime — in other words, not on an empty stomach.

young man with stomach pain sitting on couch


Acid Reflux

It seems counterintuitive that a supplement many people take for heart health would cause heartburn and acid reflux, but fish oil may, in rare cases. Symptoms may be minor, such as unpleasant fishy burps after taking the supplement, though some people develop heartburn that makes it difficult to relax.

Taking the dosage spread out throughout the day and with a meal can keep you comfortable when taking fish oil supplements.

older woman on couch with her hand on her chest


Drop in Blood Pressure

If you have high blood pressure, your doctor may recommend fish oil as an option for lowering it. However, this benefit can create issues in people who already have low numbers and take fish oil in very high doses. Low blood pressure can cause fainting, fatigue, dehydration, and other health concerns.

Fish oil can also interact with medications meant to lower blood pressure. If you are on a blood pressure medication, make sure you monitor your blood pressure levels, and let your doctor know if they get too low.

wrist with blood pressure monitor slowing a low reading


Allergic Reaction

Allergies can develop at any time; even those with no previous allergic reaction to something may develop one in the future. Of course, if you have a fish or shellfish allergy, you are at an increased risk of experiencing an allergic reaction to fish oil.

If you believe you would benefit from taking fish oil but are allergic to fish or shellfish, discuss the issue with your healthcare provider. There could be an alternative that works for you.

woman looking at red area on her upper arm


Sleep Issues

Some people find that fish oil improves the quality of their sleep. In rare cases, however, some may experience insomnia when taking the supplement, particularly in high doses. People who already find it difficult to fall or stay asleep, and those with depression, should seek medical advice before taking high doses of fish oil.

man lying awake in bed at 3 am



Fish oil is rich in omega 3 fatty acids. However, cod liver oil and other fish liver oils contain omega 3 as well as high amounts of vitamin A. Therefore, it is possible to get too much of this vitamin when taking this supplement in high doses. Signs of too much vitamin A include skin irritation, joint pain, dizziness, and nausea. If you continue to take high amounts of vitamin A, you may experience liver damage.

close up of various capsules in an amber bottle



Bleeding in the brain is known as a hemorrhagic stroke. This is different from a stroke that results from a blocked artery. There is some evidence that the excessive bleeding some people experience when taking blood thinners, as they may increase the risk of hemorrhagic stroke.

There is no proof that supplementing with fish oil increases the risk of strokes. Talk with your healthcare provider to see if the benefits of fish oil outweigh any concerns you may have.

medical concept "stroke" on clipboard with needle and stethoscope


A Boost To Your Blood Sugar

Fish oil may influence your blood sugar levels. For that reason, individuals who have diabetes and take medication should speak to a doctor before beginning to take this supplement. Numerous research studies show that fish oil may improve glycemic control, both short and long-term. However, when taken in combination with anti-diabetes drugs, high doses of fish oil may lower the glucose levels too much

hand holding blood sugar device reading low blood sugar


No Side Effects

Most people experience no side effects at all when taking fish oil. With that in mind, there are a few things you can do to increase your odds of getting only the benefits and none of the negatives of this useful supplement.

Start supplementing at the lowest recommended dose. Take a high-quality supplement from a reputable brand, as some fish oil supplements are not tested for heavy metals. Also, take the capsules with a meal to help buffer your stomach. Finally, if you have any questions or concerns at all, speak with your healthcare provider.

smiling woman about to take fish oil supplement with water


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