Fish Oil Side Effects

Normally, there are no fish oil side effects for healthy people taking a dosage of not more than 3 grams (3,000 mg) per day.

However, if you suffer from any pre-existing medical condition, take any medications with which fish oil might interact or have a fish allergy, you should consult with your physician before taking an Omega 3 fish oil supplement.

Though they are not normal, the fish oil side effects that can occur include these . . .

Gastrointestinal Upset

You may experience an upset stomach as a fish oil side effect. Diarrhea is also possible, with the symptoms being more severe with very high doses of fish oil.

Burping, heartburn and a fish aftertaste are also possible.

To reduce the chance of experiencing these gastrointestinal side effects, you can take your fish oil with meals. You may also want to start with low doses and gradually increase to your target dosage.

Metal Poisoning

You’ve probably heard that some fish, such as Largemouth Bass, Sturgeon, Shark, Swordfish, King Mackerel, farm-raised Salmon and Tilefish, can contain heavy metals, such as mercury, and other industrial and environmental contaminants including PCB’s (polychlorinated biphenyls) and dioxins. These are particularly dangerous for pregnant or nursing women.

However, this side effect applies more to eating fish directly because the oil, even in contaminated fish, carries little of the pollutants.

While it is possible for fish oil to contain these contaminates, this is not a significant problem with purified, commercial fish oil products.

Allergic Reaction

Some people who are allergic to seafood such as fish might also be allergic to fish oil supplements.

While there is no reliable information on this, it’s better to be safe than sorry. If you have a seafood allergy, you should avoid fish oil supplements or use them cautiously.


If large fish oil doses (more than 3 grams per day) are taken, the Omega 3 may increase the risk of bleeding which can take the form of a nosebleeds, blood in the urine or even a stroke.

Taken at high doses, fish oils appear to prolong bleeding time and may reduce your blood’s ability to clot.

Lowering Of Blood Pressure

People with low blood pressure and those who are taking blood pressure lowering medications should be cautious when using fish oil supplements.

That is because studies have shown that Omega 3 fatty acids cause a small reduction in blood pressure, although higher doses cause larger reductions.

You should consult with your doctor before taking fish oil supplements if you have blood pressure issues.

Vitamin E

Vitamin E plays a part in metabolizing Omega 3 fatty acids so large doses of fish oil place high demands on the body’s vitamin E supply.

To avoid this fish oil side effect, vitamin E is added to many commercial fish oil products. As a result, regular use of vitamin E-enriched products may lead to elevated levels of this fat-soluble vitamin.


Higher doses of fish oil can lower the body’s immune system response. Therefore, people whose immune system is already weak, such as those with HIV/AIDS, should be cautious about this fish oil side effect.


Only you can decide whether these possible fish oil side effects outweigh the unmistakeable benefits of taking fish oil supplements.

If any of the conditions described in this article apply to you, consult with your health care provider before you take, or increase your dosage of, fish oil supplements.

Overall, however, healthy people who take not more than 3,000 mg a day of fish oil should experience no significant side effects from taking a pure, molecularly distilled fish oil supplement.

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