Cod liver oil can be obtained from eating fresh cod liver or by taking supplements.

Cod liver oil is the oil extracted from the livers of Atlantic cod. It is commonly taken as a dietary supplement and is packed full of nutrients.
It is one of the best sources of omega 3 fatty acids (EPA and DHA), and it contains relatively high amounts of vitamin A and vitamin D.

The exact concentration of nutrients in cod liver oil depends on the species of cod, or Gadus, the oil comes from.

Uses

Cod liver oil is used as a source of vitamin A and vitamin D, and to treat high cholesterol and high triglyceride levels, kidney disease in people with diabetes, high blood pressure, heart disease, osteoarthritis, rheumatoid arthritis, depression, an autoimmune disease called systemic lupus erythematosus (SLE), glaucoma, and middle ear infections (otitis media). It is also used to prevent respiratory infections, and an age-related eye condition called macular degeneration.

Some people put cod liver oil on their skin to speed healing of wounds, burns, and rashes.

Cod liver oil contains certain "fatty acids" that prevent the blood from clotting easily. These fatty acids also reduce pain and swelling.

Safety concerns

Cod liver oil is LIKELY SAFE for most adults and children when taken by mouth. It can cause side effects including belching, bad breath, heartburn, loose stools, and nausea. Taking cod liver oil with meals can often decrease these side effects.

High doses of cod liver oil are POSSIBLY UNSAFE. They might keep blood from clotting and can increase the chance of bleeding. Vitamin A and vitamin D levels might also become too high with high doses of cod liver oil.
The safety of cod liver oil when used on the skin is unknown.

Special precautions & warnings:

Pregnancy and breast-feeding: Cod liver oil is POSSIBLY SAFE when used in amounts that provide no more than the recommended daily intakes of vitamin A and vitamin D. Cod liver oil is POSSIBLY UNSAFE when taken in larger amounts. Women who are pregnant or breast-feeding should not take cod liver oil that provides more than about 3000 mcg of vitamin A and 100 mcg of vitamin D.

Diabetes: There has been some concern that cod liver oil or other fish oils might increase blood sugar in people with diabetes. But there is no strong research that supports this concern. High blood pressure: Cod liver oil can lower blood pressure and might cause blood pressure to go too low if used along with medications for high blood pressure. Be careful when using cod liver oil if you are taking high blood pressure drugs.

Drug interactions

Be cautious with this combination.

Medications for high blood pressure (Antihypertensive drugs)

Cod liver oil seems to decrease blood pressure. Taking cod liver oil along with medications for high blood pressure might cause your blood pressure to go too low.

Herbs and supplements that lower blood pressure (Hypotensive herbs and supplements)

Cod liver oil might lower blood pressure. It has the potential to add to blood pressure lowering effects of other herbs and supplements that also lower blood pressure.

Herbs and supplements that might slow blood clotting

Cod liver oil might slow blood clotting.

Using cod liver oil with herbs and supplements that also slow blood clotting might increase the chance of bruising and bleeding in some people. These herbs include angelica, borage seed oil, clove, danshen, garlic, ginger, ginkgo, red clover, turmeric, willow, and others.