Supplement analysis backed by scientific evidence · PT

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Limited evidenceWomen's health

Evening Primrose Oil

Evening primrose oil is one of the best-studied supplements that mostly does not work. A Cochrane review of 27 trials found no benefit for eczema, and the evidence for PMS, breast pain and menopause symptoms is weak or negative.

What the science says

  • Does not improve eczema Strong evidence

    A 2013 Cochrane review pooling 27 randomized trials (including 19 of evening primrose oil, n=1,596) concluded that oral evening primrose oil is no more effective than placebo for eczema symptoms, and that further trials of this indication would be hard to justify. This is a rare case of high-quality negative evidence, and it is why regulators in the UK withdrew licences for eczema products.

  • Little effect on menopausal hot flashes Limited evidence

    A randomized trial in 56 women taking 500 mg twice daily for six weeks reported a reduction in hot flash intensity but no significant change in frequency or duration versus placebo. The trial was small, short, and has not been convincingly replicated, so this counts as a weak signal at best.

  • PMS and cyclical breast pain Limited evidence

    Trials in premenstrual syndrome and cyclical mastalgia have been small and largely null once placebo response is accounted for. The mechanistic rationale — supplying gamma-linolenic acid (GLA) to correct a supposed enzyme deficiency — has not been validated in humans.

Dosage & safety

Studied doseTrials have used 500-3,000 mg/day of oil, providing roughly 40-300 mg GLA, for 6-24 weeks. There is no established effective dose, because there is no reliably established effect.
SafetyGenerally well tolerated; nausea, headache, soft stools and abdominal discomfort are the usual side effects. Case reports link it to lowered seizure threshold, so avoid it in epilepsy and with phenothiazines. Mild antiplatelet effect — use caution with warfarin, DOACs, and antiplatelet drugs, and stop two weeks before surgery. Not recommended in pregnancy; some obstetric use to ripen the cervix has been associated with prolonged rupture of membranes and is not supported.

Scientific references

Where to buy

Solgar, Evening Primrose Oil, 1,300 mg, 60 Softgels

View on iHerb

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