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Fish oil comes from many types of fish. It is rich in two important omega-3 fatty acids called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

The benefits of fish oil seem to come from its omega-3 fatty acid content. Fish that are especially rich in these oils include mackerel, herring, tuna, and salmon. The body doesn't produce many of its own omega-3 fatty acids. Omega-3 fatty acids reduce pain and swelling, and also prevent the blood from clotting easily.

Some fish oil products are approved by the FDA as prescription medications to lower triglycerides levels. Fish oil is also available as a supplement. Fish oil supplements do not contain the same amount of fish oil as prescription products, so they cannot be used in place of prescription products. Fish oil supplements are sometimes used for heart health and mental health, but there is no strong evidence to support most of these uses.

Do not confuse fish oil with EPA, DHA, cod liver oil, flaxseed oil, krill oil, or shark liver oil. See the separate listings for these topics.

Natural Medicines rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.
  • Hypertriglyceridemia.  Oral prescription fish oil products reduce triglyceride levels in patients with hypertriglyceridemia, especially in severe cases. Oral fish oil supplements may reduce triglyceride levels when used in very high doses of up to 12 capsules per dose.
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  • Diabetes.  Oral fish oil does not improve glycemic control or prevent cardiovascular outcomes in patients with type 2 diabetes. However, oral fish oil may lower triglyceride levels in patients with type 2 diabetes.
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When taken by mouth: Fish oil is likely safe for most people in doses of 3 grams or less daily. Taking more than 3 grams daily might increase the chance of bleeding. Fish oil side effects include heartburn, loose stools, and nosebleeds. Taking fish oil supplements with meals or freezing them can reduce these issues.

Consuming high amounts of fish oil from DIETARY sources is possibly unsafe. Some fish are contaminated with mercury and other chemicals. Fish oil supplements typically do not contain these chemicals.

When applied to the skin: There isn't enough reliable information to know if fish oil is safe or what the side effects might be.

Special Precautions & Warnings:

Pregnancy and breast-feeding: Fish oil supplements are likely safe when taken by mouth. Taking fish oil does not seem to affect the fetus during pregnancy or the baby while breast-feeding. But shark, swordfish, king mackerel, and tilefish should be avoided during pregnancy, by those who may become pregnant, and while breast-feeding. These fish might contain high levels of mercury and may contain other toxins. Limit consumption of other fish to 12 ounces/week (about 3 to 4 servings/week). Consuming fatty fish in high amounts is possibly unsafe.

Children: Fish oil supplements are possibly safe when taken by mouth. In adolescents, fish oil has been used safely in doses of up to about 2.2 grams daily for 12 weeks. But young children should not eat more than two ounces of fish per week. Consuming fish oil from DIETARY sources in large amounts is possibly unsafe. Fatty fish contain toxins such as mercury. Eating contaminated fish frequently can cause serious adverse effects in children.

Bipolar disorder: Taking fish oil might increase some of the symptoms of this condition.

Liver disease: Fish oil might increase the risk of bleeding in people with liver scarring due to liver disease.

Diabetes: Taking high doses of fish oil might make it more difficult to control blood sugar levels.

Familial adenomatous polyposis: There is some concern that fish oil might further increase the risk of getting cancer in people with this condition.

Conditions in which the immune system response is lowered (including HIV/AIDS): Higher doses of fish oil can lower the body's immune system response. This could be a problem for people whose immune system is already weak.

An implanted device to prevent irregular heartbeat: Fish oil might increase the risk of irregular heartbeat in patients with an implanted defibrillator. Stay on the safe side and avoid fish oil supplements.

Fish or seafood allergy: Some people who are allergic to seafood such as fish might also be allergic to fish oil supplements. There is no reliable information showing how likely people with seafood allergy are to have an allergic reaction to fish oil. Until more is known, advise patients allergic to seafood to avoid or use fish oil supplements cautiously.

Birth control pills (Contraceptive drugs)

Interaction Rating=Moderate Be cautious with this combination.

Fish oils seem to help reduce some fat levels in the blood. These fats are called triglycerides. Birth control pills might decrease the effectiveness of fish oils by reducing these fat levels in the blood.Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.

Medications for high blood pressure (Antihypertensive drugs)

Interaction Rating=Moderate Be cautious with this combination.

Fish oils seem to decrease blood pressure. Taking fish oils along with medications for high blood pressure might cause your blood pressure to go too low.Some medications for high blood pressure include captopril (Capoten), enalapril (Vasotec), losartan (Cozaar), valsartan (Diovan), diltiazem (Cardizem), Amlodipine (Norvasc), hydrochlorothiazide (HydroDiuril), furosemide (Lasix), and many others.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Minor Be watchful with this combination.

Fish oils might slow blood clotting. Taking fish oils along with medications that also slow clotting might increase the chances of bruising and bleeding.Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.

Orlistat (Xenical, Alli)

Interaction Rating=Moderate Be cautious with this combination.

Orlistat (Xenical, Alli) is used for weight loss. It prevents dietary fats from being absorbed from the gut. There is some concern that orlistat (Xenical, Alli) might also decrease absorption of fish oil when they are taken together. To avoid this potential interaction take orlistat (Xenical, Alli) and fish oil at least 2 hours apart.

Herbs and supplements that might lower blood pressure: Fish oil might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.
Herbs and supplements that might slow blood clotting: Fish oil might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.
Vitamin D: Taking fish oil may increase vitamin D levels. This seems to only occur in people who have low vitamin D levels.
Vitamin E: Fish oil might reduce vitamin E levels. Researchers aren't sure if this is because fish oil keeps vitamin E from being absorbed from food or because it causes the body to use up vitamin E faster than it should.

There are no known interactions with foods.

Fish oil supplements have most often been used by adults in doses of up to 6 grams daily by mouth for up to 12 weeks. Fish oil products typically provide 180-465 mg of EPA and 120-375 mg of DHA per capsule. Fish oil is also available in prescription drugs, including Lovaza, Omtryg, and Epanova. Fish oil supplements cannot be used in place of fish oil prescription drugs. Speak with a healthcare provider to find out what product and dose might be best for a specific condition.

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