People who take fish oil tablets in the hope it will ease anxiety or depression are wasting their time, say Norwich researchers, who have found they have little or no effect.
And University of East Anglia scientists say, given environmental concerns over industrial fishing and the impact on fish stocks, people might want to stop swallowing the tablets.
Increased consumption of omega-3 fats is widely promoted globally because of a common belief that it will protect against, or even reverse, conditions such as anxiety and depression.
Omega-3 is a type of fat. Small amounts are essential for good health and can be found in the food such as nuts, seeds and fatty fish, such as salmon.
Omega-3 fats are also available as over-the-counter supplements, but a systematic review published in the British Journal of Psychiatry, finds they offer no benefit.
The research team looked at 31 trials of adults with and without depression or anxiety.
More than 41,470 participants were randomised to consume more long-chain omega-3 fats (fish oils), or maintain their usual intake, for at least six months.
They found the supplements had little or no effect in preventing depression or anxiety symptoms.
Lead author Dr Lee Hooper, from UEA's Norwich Medical School, said: "Our previous research has shown that long-chain omega-3 supplements, including fish oils, do not protect against conditions such as heart disease, stroke, diabetes or death.
"This large systematic review included information from many thousands of people over long periods. Despite all this information, we don't see protective effects.
"The most trustworthy studies consistently showed little or no effect of long-chain omega-3 fats on depression or anxiety, and they should not be encouraged as a treatment."
Dr Katherine Deane, from UEA's School of Health Sciences, said oily fish can be a very nutritious food as part of a balanced diet, but added: "Considering the environmental concerns about industrial fishing and the impact it is having on fish stocks and plastic pollution in the oceans, it seems unhelpful to continue to swallow fish oil tablets that give no benefit."
The research was funded by the World Health Organisation.
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