Omega-3 fatty acids may cause bloody urine, abnormal heart rhythm, nausea and acid reflux. Other possible side effects include abnormally high urination, burping, dizziness and diarrhea. Some people may experience skin problems, tiredness, weight gain or constipation, according to Mayo Clinic.
Omega-3 fatty acids may cause a burning or prickling feeling, a shift in physical activity and energy, mania and memory problems. Other possible side effects include nosebleed, restlessness, fainting and a feeling of ants crawling on the skin. Additional potential side effects include sudden cardiac arrest, fishy hiccups, bloating and bad breath. Some people may experience indigestion, the common cold, muscle swelling or pain, or a feeling of lifelessness, notes Mayo Clinic.
People who are allergic to fish should avoid fish-based omega-3 fatty acid supplements. People with bleeding disorders should speak to a physician before taking omega-3 fatty acid supplements, as they may increase the risk of bleeding. People with diabetes or other conditions related to blood sugar should speak to a health care provider before taking omega-3 fatty acids, as they may affect blood sugar levels, states Mayo Clinic.
Because omega-3 fatty acids can lower blood pressure, people taking medications that lower blood pressure should speak to a doctor or pharmacist before taking omega-3 fatty acid supplements, notes Mayo Clinic.