Known botanically as Oenothera biennis, oil of evening primrose (OEP or EPO) is used by women to help relieve breast pain and symptoms of the premenstrual syndrome. OEP is also believed by some to decrease the risk of other conditions, such as cardiovascular disease and rheumatoid arthritis.
The oil of Evening Primrose has been sought after due to its content of gamma-linolenic acid (GLA). Evening Primrose Oil contains 8-10% GLA (Omega 6), 50-70% cis-linoleic acid (Omega 6), and small amounts of oleic, palmitic, and stearic acid. As a source of both GLA and other the Omega 6 essential fatty acid, EPO is often taken as a daily supplement by many.
EPO can be found in soft-gel capsules containing 500-1300mg. While the oil is not listed, both flower and root preparations of Oenothera biennis are listed as "Approved" for respiratory inflammations by the German Commission E.
Most studies evaluating the use of OEP have used products containing 72% cis-linoleic acid and 9% GLA. Patients should use a brand of OEP that contain these amounts of fatty acids, and they should follow the manufacturer's guidelines for dosing.
The effects of OEP are attributed to its high concentrations of the fatty acids cis-linoleic acid and cis-y-linolenic acid (GLA). Both are produced in the body in limited amounts. Women with breast pain have reduced levels of GLA (most likely secondary to decreased conversion of cis-linoleic acid to GLA).
Supplementation of 2.4-3.2gm/day of OEP (in divided doses) has been shown to decrease pain in 44% of women with cyclical breast pain and 27% of those with non-cyclical breast pain. OEP must be taken for at least four months before its effects will be felt, because its onset is delayed.
Women with PMS are also believed to have decreased conversion of cis-linoleic acid to GLA. The resulting reduction in GLA levels leads to deficient synthesis of prostaglandin E1, which is thought to aggravate PMS symptoms. In one study, administration of 4 capsules of OEP (each containing 72% linoleic acid and 9% GLA) twice daily during the last 14 days of the menstrual cycle relieved PMS symptoms. However, conclusive results concerning the effectiveness of OEP for PMS are lacking, because other studies have shown no effect.
OEP is relatively free of side-effects, although mild gastrointestinal irritation has been reported. OEP has no known drug interactions.
In a preliminary trial, supplementing with evening primrose oil (approximately 1,600mg per day) led to a 10% increase in exercise tolerance in people with intermittent claudication. [Christie SB, Conway N, Pearson HE. Observations on the performance of a standard exercise test by claudicants taking gamma-linolenic acid. J Atheroscler Res 1968;8: pp.83-90]