Fish oil supplements may cause side effects such as an unpleasant smell and gastrointestinal symptoms. Limited evidence suggests it may also increase the risk of bleeding and prostate cancer.
Certain fish and their oils contain healthful fats that health experts recommend people regularly consume in their diets.
Despite fish oil’s potential health benefits, people may also experience certain side effects, including gastrointestinal upset, reduced blood clotting, and allergic reactions.
The side effects a person may experience from fish oil depend on several factors. These include the person’s overall health, whether they take any medications, and if they have any risk factors for fish oil complications.
Most people who take fish oil supplements do not experience any serious side effects. However, it is a good idea to talk with a doctor before taking fish oil supplements, especially if using it for a specific medical condition.
Fish and fish oil have a distinctive odor. Some people report that fish oil tastes bad or leaves an unpleasant taste in their mouths. Others say it causes bad breath, which is typically mild and may resolve with a lower dose.
More research is necessary to understand the potential link between fish oil and bad breath.
If people dislike the taste or smell of fish oil supplements or feel that it leaves a lingering scent but wish to keep taking it, they can speak with a doctor about ways to potentially disguise or reduce the smell or taste.
Fish oil has an antiplatelet effect, which means it can prevent the blood from clotting. This property may help explain some of its heart health benefits since thinning the blood may improve cardiovascular health.
A 2024 review found no association between omega-3 fatty acid supplements and an increased bleeding risk unless people took a very high dose. Even then, the risk was not clinically significant.
However, people taking antiplatelet or anticoagulant medications
People on these medications should always speak with a healthcare professional before taking fish oil supplements.
As with many other supplements and medications, some people experience gastrointestinal problems after taking fish oil,
Sometimes, lowering the dosage or taking fish oil with food may relieve these side effects. Some people may need to stop using fish oil supplements.
An older
However, the study’s authors state that further work was necessary to prove the cause. Other research also suggests the opposite.
For example, a 2024 review of 11 trials found no increased risk of gastrointestinal bleeding or fatal bleeding events in any of the included studies.
Animal research also suggests that fish oil supplementation may help neutralize stomach acidity, which improves ethanol-induced stomach ulcers in rats. However, more research is necessary.
People can develop an allergy to any food or supplement, including fish oil.
Someone with a fish or shellfish allergy may be at risk of an allergic reaction to fish oil. They should consult their doctor before taking fish oil supplements.
Symptoms of an allergic reaction may include:
- tingling or itching in the mouth
- hives
- swelling of the mouth, lips, or throat
- gastrointestinal symptoms, such as
- stomach pain
- diarrhea
- vomiting
Anyone with severe symptoms, including difficulty breathing, after taking fish oil should seek immediate medical help.
There is mixed evidence about fish oil and prostate cancer.
An older observational 2015 study found a positive association between increased prostate cancer risk and high levels of omega-3 in the blood.
However, the researchers caution that more research is necessary to understand whether there is a cause-and-effect relationship.
Another 2021 study involving 5,601 men between 40 and 80 years old found no evidence that suggests consuming fish oil or supplements significantly affects the risk of prostate cancer.
More research is necessary to understand if there is a link between fish oil and prostate cancer risk. Anyone with concerns about their prostate cancer risk can discuss it with a healthcare professional.
The United States Department of Agriculture’s Dietary Guidelines for Americans 2020 to 2025 recommends eating at least
There are no specific recommendations in the guidelines on the amount of omega-3 fatty acids someone should take. It may depend on various factors, such as their age and their state of health.
The National Institutes of Health suggests an adequate daily intake of omega-3 fatty acids for most adults is between
Many studies of fish oil use small doses of a few grams (g) per day. Larger doses, such as 20 g per day, may cause more side effects.
People can start with a small amount each day and talk with a doctor before increasing the dosage.
If someone notices an unpleasant smell or other minor side effects, they may want to decrease the dosage to see if that helps.
Anyone who develops serious complications, such as an allergic reaction, rash, vomiting, or breathing difficulties, should stop taking fish oil and seek emergency help.
Although many people take fish oil or its supplements without adverse effects, potential side effects can include an unpleasant smell or taste, allergic reactions, and gastrointestinal symptoms.
If someone experiences side effects, their doctor may recommend lowering their fish oil dosage or stopping altogether to resolve their symptoms.
People should speak with a healthcare professional before starting a new supplement. In some cases, people may already get enough omega-3 fatty acids and other important nutrients through their diet.