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Oct. 21, 2002 -- It may sound fishy, but researchers say taking a daily fish-oil supplement may boost the effectiveness -- or even replace -- antidepressants for treating depression in some people.

In a new study, people who added a daily dose of omega-3 fatty acids to their regular antidepressant treatment had significant improvement in symptoms, including anxiety, sleeping problems, sadness, decreased sexual desire, and suicidal tendencies.

Although there are many effective treatments for depression, most only work in a limited number of patients or have significant side effects that prompt users to stop taking them. That's inspired researchers to look for new ways to treat the mental illness or increase the effectiveness of existing treatments.

Previous studies have suggested that depressed people have lower-than-normal levels of a fatty acid known as EPA (eicosapentaenoic acid), which plays an important role in maintaining normal brain function.

In this study, the researchers examined the effectiveness of adding various dosages of EPA supplement to normal drug therapy in 70 people with persistent depression that was not responding to standard antidepressants. The results appear in the October issue of the Archives of General Psychiatry.

Researcher Malcolm Peet, MD, of Swallownest Court Hospital in Sheffield, England, and colleagues found that patients who took the lowest, 1-gram daily, fish-oil dose showed significant improvements on all major measures of depression compared with those who took a placebo. In particular, 69% of the patients who took the 1-gram dose had a 50% reduction in their symptoms, compared with only 25% of those who took a placebo.

A 2-gram dose showed little effect, but those taking the highest, 4-gram, dose showed a trend toward improvement in symptoms. The researchers say larger studies are needed to confirm these effects.

The omega-3 fatty acid may work to ease depression by improving the effectiveness and absorption of existing medications, the researchers say. But they note that a limited number of their patients who are not on antidepressant therapy have seen improvements similar to those seen in this study through treatment with fish-oil supplements alone.

In addition, they say treatment with omega-3 fatty acid may be especially beneficial for depressed patients who are at risk for heart disease, in light of recent research about fish oil's heart-healthy effects.