Fish oil supplements, generally derived from the fatty tissues of cold-water fish, contain a complex of omega-3 fatty acids. These nutritionally essential compounds provide numerous nutritional benefits and might help to improve the health of the cardiovascular, ocular and central nervous systems. Although moderate doses of fish oil are safe and likely beneficial, excessive doses potentially cause several side effects impacting the health of the nervous system.
Stroke Risk
Very high doses of fish oil might increase the risk of hemorrhagic stroke -- bleeding in the brain -- which causes permanent or fatal damage to the brain and central nervous system. A study published in the January 2001 issue of the "Journal of the American Medical Association" determined that high doses of fish oil decrease the risk of thrombotic stroke, caused by clogged arteries, but have no impact on the risk of hemorrhagic stroke. The University of Maryland Medical Center recommends avoiding fish oil doses higher than 3 grams per day to minimize the risk of hemorrhagic stroke.
Mental Health
Fish oil might have an impact on mental health. According to MedlinePlus, fish oil could either improve or worsen some symptoms of bipolar disorder, schizophrenia and clinical depression. More studies are needed to weigh the relative benefits and risks of fish oil for people with mental health disorders. Consult your health care provider before taking fish oil if you have a mental illness.
Attention and Hyperactivity
Fish oil is one of many potential naturopathic treatments for attention deficit hyperactivity disorder (ADHD). Large doses might help to reduce the neurobehavioral symptoms associated with the condition, especially in children. However, the UMMC notes that evidence of its efficacy is mixed, and that some studies have found little or no benefit. More well-designed clinical trials are necessary to determine how and if fish oil affects the neurological function of people with ADHD.
Contamination Risk
In theory, contaminants in fish oil could cause heavy metal poisoning, damaging the central nervous system. The University of Maryland Medical Center acknowledges that potentially high levels of mercury exist in some species of fish -- most notably mackerel, tuna, swordfish and tilefish. These contaminants are generally present in the flesh, not the oil, of the fish.
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