According to WebMD, the side effects of fish oil can include belching, bad breath, heartburn, nausea, rash, loose stools and nosebleeds. In addition, taking fish oil in high doses over 3 grams per day can increase the chance of bleeding and may keep blood from clotting.
The University of Maryland Medical Center notes that clinical evidence and research supports the benefits of using fish oil for heart conditions, such as high blood pressure, high cholesterol and heart disease. People take fish oil supplements to aid in a variety of ailments, including arthritis, depression, skin disorders, asthma, menstrual pain and certain cancers.
The U.S. Food and Drug Administration states that the omega-3 fatty acids found in fish are safe to take as a dietary supplement. The daily intake from food and supplement sources should not exceed 3 grams due to potential bleeding issues, according to the University of Maryland Medical Center.
The Mayo Clinic warns people with known shellfish or seafood allergies not to take fish oil as reactions and rashes have been reported. Pregnant or breastfeeding women must also use caution due to the potential of mercury in fish. Most of the side effects of taking fish oil are minor and can be prevented.