Written by Rachael Link, MS, RD 
July 17, 2018

Fish oil is well known for its wealth of health-promoting properties.

Rich in heart-healthy omega-3 fatty acids, fish oil has been shown to reduce blood triglycerides, relieve inflammation and even ease symptoms of conditions such as rheumatoid arthritis (1).

However, more fish oil is not always better, and taking too high a dose may actually do more harm than good when it comes to your health.

Here are 8 potential side effects that can occur when you consume too much fish oil or omega-3 fatty acids.

1. High Blood Sugar

Some research shows that supplementing with high amounts of omega-3 fatty acids could increase blood sugar levels in people with diabetes.

One small study, for example, found that taking 8 grams of omega-3 fatty acids per day led to a 22% increase in blood sugar levels in people with type 2 diabetes over an eight-week period.

This is because large doses of omega-3s can stimulate the production of glucose, which can contribute to high levels of long-term blood sugar levels.

However, other research has turned up conflicting results, suggesting that only very high doses impact blood sugar.

In fact, another analysis of 20 studies found that daily doses of up to 3.9 grams of EPA and 3.7 grams of DHA — the two main forms of omega-3 fatty acids — had no effect on blood sugar levels for individuals with type 2 diabetes.

2. Bleeding

Bleeding gums and nosebleeds are two of the hallmark side effects of excess fish oil consumption.

One study in 56 people found that supplementing with 640 mg of fish oil per day over a four-week period decreased blood clotting in healthy adults.

Additionally, another small study showed that taking fish oil may be linked to a higher risk of nosebleeds, reporting that 72% of adolescents taking 1–5 grams of fish oil daily experienced nosebleeds as a side effect (7).

For this reason, it’s often advised to stop taking fish oil prior to surgery and to talk to your doctor before taking supplements if you’re on blood thinners like Warfarin.

3. Low Blood Pressure

Fish oil’s capacity to lower blood pressure is well documented.

One study of 90 people on dialysis found that taking 3 grams of omega-3 fatty acids per day significantly decreased both systolic and diastolic blood pressure compared to a placebo (8).

Similarly, an analysis of 31 studies concluded that taking fish oil can effectively lower blood pressure, especially for those with high blood pressure or high cholesterol levels (9).

While these effects can certainly be beneficial for those with high blood pressure, it can cause serious problems for those who have low blood pressure.

Fish oil may also interact with blood pressure-lowering medications, so it’s important to discuss supplements with your doctor if you’re receiving treatment for high blood pressure.

4. Diarrhea

Diarrhea is one of the most common side effects associated with taking fish oil, and may be especially prevalent while taking high doses.

In fact, one review reported that diarrhea is one of the most common adverse effects of fish oil, alongside other digestive symptoms such as flatulence (10).

In addition to fish oil, other types of omega-3 supplements may also cause diarrhea.

Flaxseed oil, for example, is a popular vegetarian alternative to fish oil, but has been shown to have a laxative effect and may increase bowel movement frequency (11).

If you experience diarrhea after taking omega-3 fatty acids, make sure you’re taking your supplements with meals and consider decreasing your dosage to see if symptoms persist.