However, evidence that it might not be as effective as customers believe in treating a wide range of ills has not affected sales. The market was pounds 36m in 1993, compared with pounds 17m in 1991. Typically, a pot of 60 capsules, each 500mg, costs pounds 5.90.
One study last year in the Lancet questioned its efficacy in treating eczema and another from Sweden found it no better than a placebo for treating symptoms of pre-menstrual syndrome.
The new study, published today in the British Medical Journal by the Academic Department of Obstetrics and Gynaecology at Keele University in Staffordshire, monitored 35 menopausal women. It found the placebo - liquid paraffin capsules - appeared to help more with hot flushes over seven months.
The researchers recruited 56 menopausal women, all experiencing hot flushes at least three times a day. Half took evening primrose oil and half liquid paraffin capsules.
The women were asked to complete diary cards daily on their symptoms. Only 17 in one group and 18 in the other completed the six-month course, in all cases those giving up did so because their symptoms were not being relieved.
Evening primrose oil is a rich source of gamma-linoleic acid or gamolenic acid (GLA) and is being used increasingly by women as an alternative to hormone
replacement therapy for the menopause.
The researchers conclude: 'Based on the data from this small pilot study and on the lack of a hypothetical rationale for using gamolenic acid, we cannot support the use of evening primrose oil in the treatment of menopausal hot flushes.'
Evening primrose oil has another problem. The plant borage, borage officinalis, has been found to contain 15 per cent more GLA and consequently can be sold more cheaply.Reuse content