The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
People with a known allergy or hypersensitivity to fish should avoid fish oil or omega-3 fatty acid products derived from fish. Skin rash has been reported rarely. People with a known allergy or hypersensitivity to nuts should avoid alpha-linolenic acid or omega-3 fatty acid products that are derived from the types of nuts to which they react.
Side Effects and Warnings
The U.S. Food and Drug Administration (FDA) classifies intake of up to three grams of omega-3 fatty acids from fish daily as GRAS (generally regarded as safe).
Fish oil supplements may cause nausea, diarrhea, loose stools, decreased appetite, constipation, vomiting, and fat in the stools. Gastrointestinal side effects may be minimized if fish oils are taken with meals and if doses are started low and gradually increased.
Mild elevations in liver function tests (alanine aminotransferase) have been reported rarely.
There are rare reports of mania in patients with bipolar disorder or major depression. Restlessness and formication (the sensation of ants crawling on the skin) have also been reported.
Other potential side effects include loss of short-term memory, headache, hemolytic anemia (abnormal breakdown of red blood cels), depression, somatic disorders (physical symptoms associated with psychological symptoms), increased risk of colon cancer, nasopharyngitis (inflammation in nose and throat), worsening of asthma symptoms, decreased physical activity, increased appetite, increased blood pressure, and an uncomfortable feeling.
Fish meat may contain potentially harmful contaminants, such as dioxins, methylmercury, and polychlorinated biphenyls (PCBs). Caution is warranted in young children and pregnant or breastfeeding women.
Omega-3 fatty acids may increase blood sugar levels. Caution is advised in patients with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
Omega-3 fatty acids may increase low-density lipoprotein (LDL, or "bad") cholesterol levels. Caution is advised in patients with high levels of LDL cholesterol.
Omega-3 fatty acids may worsen symptoms for patients with ventricular tachycardia (rapid heartbeat). Use cautiously in patients with ventricular tachycardia (rapid heartbeat) or ventricular arrhythmia (abnormal heart rhythm).
Omega-3 fatty acids may increase the risk of bleeding. Caution is advised in patients with bleeding disorders or those taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
Omega-3 fatty acids may decrease blood pressure. Caution is warranted in patients with low blood pressure or in those taking blood pressure-lowering medications.
Fish oil taken for many months may cause a deficiency of vitamin E and may increase the risk of vitamin A or D toxicity. Use large amounts cautiously.
Use cautiously in individuals at risk for hormone imbalance or those undergoing hormone replacement therapy, as decreased estrogen receptor production has been associated with fish oil supplementation.
Use cautiously in patients with asthma, inflammatory bowel disease, or liver disease, and in patients at risk for colon cancer, based on potential adverse effects associated with fish oil use.
Avoid in individuals with a known hypersensitivity or allergy to fish oil or omega-3 fatty acid products derived from fish. Skin rashes have been reported rarely. Individuals with a known allergy or hypersensitivity to nuts should avoid alpha-linolenic acid or omega-3 fatty acid products that are derived from the types of nuts to which they react.
Pregnancy and Breastfeeding
Potentially harmful contaminants, such as dioxins, methylmercury, and polychlorinated biphenyls (PCBs), are found in some species of fish and may be harmful in pregnant or nursing women. Methylmercury accumulates in fish meat more than in fish oil, and fish oil supplements appear to contain almost no mercury. Therefore, these safety concerns apply to eating fish but likely not to ingesting fish oil supplements. However, unrefined fish oil preparations may contain pesticides.
It is not known if omega-3 fatty acid supplementation of women during pregnancy or breastfeeding is beneficial to infants. It has been suggested that high intake of omega-3 fatty acids during pregnancy, particularly DHA, may increase birthweight and gestational length. However, higher doses may not be advisable due to the potential risk of bleeding. Fatty acids are added to some infant formulas.
The U.S. Environmental Protection Agency (EPA) recommends that fish intake be limited in pregnant and nursing women to a single six-ounce meal per week, and in young children to less than two ounces per week.
Women who might become pregnant are advised to eat seven ounces of fish with higher levels of methylmercury or less per week, or up to 14 ounces per week of fish types with about 0.5 parts per million (such as marlin, orange roughy, red snapper, or fresh tuna).