Fish oil may help relieve inflammatory symptoms of these auto-immune diseases by suppressing the immune response. More than a dozen studies have suggested that high doses of fish oil supplements taken long term and with pain medication can reduce joint swelling, ease morning stiffness, and lessen fatigue in people with rheumatoid arthritis. There is also some preliminary evidence that fish oil may help reduce the itching and redness of psoriasis, another auto-immune disease. Fish are able to convert the linolenic acid in algae and other sea plants into EPA and DHA, but humans can do so only to a limited degree. The decreased ability of your blood to clot has a negative side, notably an increased risk of hemorrhagic stroke.
Large doses can cause nausea, diarrhea, belching, and a bad taste in the mouth.
Fish oil in liquid or capsule form may contain pesticides or other contaminants. These are usually removed in the manufacturing process, but there's no guarantee. Cod liver oil is overly rich in vitamins A and D, which can be toxic in high doses. There's no reason to take it. Large doses of fish oil may suppress certain aspects of the immune system.