Evening Primrose Oil for Premenstrual Syndrome
Clinical bottom line: There is no evidence from high quality studies to show that evening primrose oil reduces the symptoms of premenstrual syndrome, including cyclical mastalgia. The included studies were small and of variable quality.
Premenstrual syndrome is associated with a mixture of emotional, somatic and behavioural symptoms. It is thought to result from disruption to the normal levels of certain fatty acids in the body. Evening primrose oil (EPO) contains the essential unsaturated fatty acids linoleic and
gamma-linoleic acid. The latter is thought to be helpful in restoring the body's natural balance of fatty acids.
Findings:
The included studies were of variable quality and were small. Women rated their symptoms over a treatment period of between 2-6 menstrual cycles.
Cyclical mastalgia:
Two randomised, cross-over studies compared EPO with liquid paraffin in women with cyclical mastalgia and noncyclical mastalgia (109 patients) over 3-4 cycles. The studies were described as double blind, but all patients received EPO at the cross-over. This removes the blinding from the second treatment phase. The dose of EPO was six capsules per day.
There was no significant, clinically relevant difference in breast tenderness, nodularity, pain, heaviness or lumpiness with EPO.
Premenstrual symptoms:
Six randomised, double blind studies compared EPO with liquid paraffin in 287 women with premenstrual symptoms over 2-6 cycles. In two studies, patient ratings showed no difference between EPO and liquid paraffin for breast pain, swelling and tenderness. Four studies (222 women) assessed mood, abdominal swelling, tiredness etc. Of these two were positive, one showed no difference between EPO and placebo, and one did not report its results.Five open, uncontrolled studies showed positive beneficial effects of EPO in 744 women with premenstrual symptoms. Response rates varied between 26-86%.
Adverse effects
The incidence of adverse effects was low and included rash, nausea, abdominal bloating, depression, dizziness. All adverse effects were also reported with placebo and included premenstrual symptoms. No further details were provided.
Comment
There is no compelling evidence of any additional beneficial effect of Evening Primrose Oil over that reported with placebo in any of the more methodologically rigorous studies. Two studies which were described as double blind were only blind for the first treatment phase. All of the studies were small and some were not controlled. The open studies are likely to be biased because of the lack of blinding. Their positive results are also likely to be invalid because of high placebo response rates in EPO trials.
