In a small study of teenagers and young adults at high risk of developing a psychotic disorder, those who took fish oil were over five times less likely to develop such a disorder. The study ran for a full year.

This protection is thought to come from omega−3 fatty acids present in fish. Abnormal fatty acid metabolism may play a role in the development of one psychotic disorder, schizophrenia. But what the study actually tested was fish oil, which is oil obtained from cooked, pressed fish. While high in omega−3 fatty acids, fish oil contains many other compounds.

There are at least as many reasons against prescribing antipsychotic drugs as there are for using them.

Generally, a psychotic disorder is one that involves a break with reality, usually in the form of a delusion or hallucination. More precise definitions get complicated because there is no universally accepted definition of the word psychotic. The definition of psychotic given in the glossary of American Psychiatric Association's diagnostic manual (DSM−IV) is over 150 words long.

At the moment, there is no state−of−the−art guideline on how to treat younger individuals who are deemed at high risk for psychotic illness. This is especially true for minors. Antipsychotic drugs may be helpful, but they also have serious side effects, may be stigmatizing, and trials of such medications have rarely been conducted on subjects younger than 18. Add to this the fact that only one−third of all people judged as high risk for psychotic disorders will develop a full−fledged illness in any given year and that many younger individuals do not want to commit to a treatment they may need to continue for five or ten years, and there are at least as many reasons against prescribing antipsychotic drugs as there are for using them.

Fish oil may offer a safer and more acceptable alternative that's just as effective.

The study was of 81 individuals, aged 13−25. They were judged as high−risk for psychotic illness for one of three reasons: they had displayed continuous low−level psychotic symptoms, displayed transient psychotic symptoms, or had either a schizophrenia−like personality disorder or a close relative with schizophrenia, combined with a sharp decline in their own mental function over the past year. Forty−one subjects took fish oil capsules (containing 1.2 grams of omega−3 fatty acids) for 12 weeks, while 40 took dummy capsules. The subjects were followed for 40 weeks after they ceased to take medication, making the study a full year long.

At the study's conclusion, only 2 of the subjects who had taken fish oil (5%) had developed a psychotic disorder, compared to 11 of those who took the dummy capsules (28%). People taking fish oil also showed improvements in social function.

Particularly important is that 76 of the 81 participants completed the trial. This shows that fish oil was tolerated well by the subjects, something that is not always true of conventional antidepressants.

The researchers note that if larger studies confirm these results, fish oil could potentially be used to prevent or treat chronic depression, bipolar disorder and substance abuse disorder, conditions which are much more common than psychotic illness is. The researchers themselves have a larger study in the works.

The results of the study were published in the February 2010 issue of the Archives of General Psychiatry.