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In people with diagnosed depressive disorders, EPA omega-3 fatty acids improve depression symptoms

Hallahan B, Ryan T, Hibbeln JR, et al. Efficacy of omega-3 highly unsaturated fatty acids in the treatment of depression. Br J Psychiatry. 2016;209:192-201.

Review questions

In people who have major depressive disorder or bipolar disorder, do omega-3 fatty acids improve symptoms? In people without a diagnosed depressive disorder, do omega-3 fatty acids prevent depression symptoms?


Depression is a common mood disorder that affects how you feel, think, and behave. It may be mild or more severe and persistent (major depression). Symptoms include feeling sad, losing interest in things you like to do, having trouble thinking or concentrating, or feeling anxious or restless. Bipolar disorder causes extreme mood swings from emotional highs (mania or hypomania) to lows (depression).

Depression is more than just being sad and may get worse if not treated. There are many treatments for depression including drugs, psychotherapies, and other treatments (e.g., exercise, acupuncture, supplements).

Fish oil and certain plant and nut oils provide omega-3 fatty acids through food. Fish oil contains two omega-3 fatty acids called docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

How the review was done

The researchers did a systematic review, searching for studies published up to July 2014. They found 35 randomized controlled trials with 11,038 people.

The key features of the trials were:

  • people had a diagnosis of major depressive disorder, bipolar disorder, or a depressive episode where they tried to hurt themselves; or people did not have a diagnosed depressive disorder;
  • and omega-3 fatty acids were compared with placebo.

The researchers grouped studies by DHA and EPA omega-3 fatty acids, and by people with diagnosis of a depressive disorder and those without depressive disorders.

Outcomes were depression symptoms.

What the researchers found

DHA omega-3 fatty acids did not improve depression symptoms.

EPA omega-3 fatty acids improved depression symptoms in people with diagnosed disorders.

EPA omega-3 fatty acids did not prevent depression symptoms in people who did not have a diagnosed disorder.


In people with diagnosed depressive disorders, eicosapentaenoic acid (EPA) omega-3 fatty acids improve depression symptoms more than placebo. Omega-3 fatty acids do not prevent depression in people who have not been diagnosed with a depressive disorder.

Omega-3 fatty acids vs placebo in people with or without diagnosed depressive disorders

Type of omega-3 fatty acid


Number of trials (number of people)

Effect on depression symptoms

Docosahexaenoic acid (DHA)

With or without depressive disorder

12 trials (3381 people)

No difference in effect

Eicosapentaenoic acid (EPA)

With or without depressive disorder

26 trials (6292 people)

EPA improved symptom scores more than placebo

Eicosapentaenoic acid (EPA)

Depressive disorder

19 trials (5038 people)

EPA improved symptom scores more than placebo

Eicosapentaenoic acid (EPA)

No depressive disorder

7 trials (969 people)

No difference in effect



A harmless, inactive, and simulated treatment.
Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.
Systematic review
A comprehensive evaluation of the available research evidence on a particular topic.

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