Bottom Line: Evening primrose oil has not been shown to treat or prevent cancer.
Scientists have not figured out how exactly evening primrose oil exerts its effects, but theorize that it has anti-inflammatory activity. It may be beneficial for patients with mastalgia (breast pain). It may also help those with diabetes, heart disease, cancer, premenstrual syndrome, eczema, high cholesterol conditions but there is no enough data to support such effects.
To treat cancer Evening primrose oil had no effect on tumor size or survival in patients with liver cancer. In another study, patients with breast cancer who received GLA in addition to Tamoxifen had faster response to treatment than those who received Tamoxifen alone.
To treat diabetic neuropathy Studies in animals suggest that evening primrose oil can prevent or reverse diabetic neuropathy, and one clinical trial almost 20 years ago supported this use. However, more research is needed.
To treat eczema Clinical trials show conflicting results.
To treat gastrointestinal disorders such as colitis or irritable bowel syndrome One clinical trial has studied the effects of evening primrose oil on ulcerative colitis, showing weak effects. In general, there is little support for this use.
To reduce high cholesterol One small clinical trial suggested that evening primrose oil led to a decrease in LDL ("bad") cholesterol, but these findings have not been confirmed by additional studies.
To relieve breast pain (mastalgia) A handful of clinical trials support this use, especially for mastalgia associated with the menstrual cycle.
To relieve menopausal symptoms One clinical trial found that evening primrose oil was no better than placebo at relieving menopausal hot flashes. No other scientific evidence supports this use.
To prevent premenstrual syndrome (PMS) Results of clinical trials are inconsistent.
To reduce inflammation of rheumatoid arthritis Two clinical trials have shown an improvement in subjective symptoms of rheumatoid arthritis, but no changes in the actual disease process.
Rheumatoid arthritis: Fifty-six patients with rheumatoid arthritis took part in a clinical trial of gamma linolenic acid (GLA), the active component of evening primrose oil. Half of the patients took GLA capsules for six months, while the other half took a sunflower seed oil placebo during this time. The patients taking GLA had a significant improvement in symptoms, so the researchers switched all of the patients to GLA for an additional six months without telling them. In this time, patients reported additional improvements in symptoms.
Premenstrual syndrome (PMS): A meta-analysis compiled and analyzed the results of seven clinical trials that used evening primrose oil to prevent premenstrual syndrome. Overall, evening primrose oil had no consistent effect on premenstrual syndrome. However, most of the clinical trials were small, so it may be the case that no effect was seen simply because there were too few patients. Nonetheless, on current evidence, evening primrose oil is of little value in the management of premenstrual syndrome.
Diabetic neuropathy: In a randomized, controlled trial studying the effects of evening primrose oil on diabetic neuropathy, 111 patients were given either 6 grams of evening primrose oil or a placbeo pill per day and were followed for 12 months. The group taking evening primrose oil showed statistically significant improvements in symptoms, and treatment appeared to be more effective in patients whose diabetes was more well-controlled.
Mastalgia (breast pain): The results of several clinical trials and volunteer studies conducted in the United Kingdom were compiled to measure the effect of evening primrose oil on mastalgia (breast pain). Overall, evening primrose oil was found to have a similar level of effectiveness as bromocriptine (a drug used to treat mastalgia), having beneficial effects in 44% of women treated. However, this was less effective than treatment with danazol, another medication. Treatment with evening primrose oil was more effective in women with cyclical mastalgia (coming and going with the menstrual cycle) than in women with non-cyclical pain. Another study found evening primrose oil is no more effective than wheat-germ oil in the treatment of breast pain.
Breast Cancer: Thirty-eight breast cancer patients participated in a study testing the effectiveness of GLA in conjunction with the chemotherapy drug, Tamoxifen. Each patient received GLA along with Tamoxifen for six months. Results were compared with a seperate group of forty-seven patients who had received Tamoxifen alone. Results showed that the patients taking GLA in addition to Tamoxifen had a significantly faster response to the treatment than those on the chemotherapy agent alone. This change in response was noticed as early as six weeks into the course of treatment.
This product is regulated by the FDA as a dietary supplement. Unlike approved drugs, supplements are not required to be manufactured under specific standardized conditions. This product may not contain the labeled amount or may be contaminated. In addition, it may not have been tested for safety or effectiveness.
You are taking anticoagulants or antiplatelet agents - 'blood thinners'
You are taking phenothiazines such as fluphenazine (Evening primrose oil may lower the seizure threshold and increase the risk of seizures in patients taking phenothiazines).
Derived from the plant Oenothera biennis, evening primrose oil (EPO) is used for rheumatoid arthritis, premenstrual syndrome, eczema, fatigue, diabetic neuropathy and mastalgia. EPO contains gamma-linolenic acid (GLA), a primary fixed oil that is converted to dihomo-gamma-linolenic-acid, a prostaglandin precursor (2)(3). In vitro studies indicate that EPO may inhibit platelet aggregation (6)(7). Clinical efficacy data are inconsistent, although one study showed GLA to be an effective adjunctive therapy for breast cancer (4). Conclusions from a meta analysis indicate that EPO is ineffective in treating mastalgia (1). GLA may prevent weight regain in individuals who recently experienced major weight loss (5). Adverse reactions include headache and GI disturbances. EPO should not be taken during pregnancy (8). One study reported a reduced seizure threshold when EPO was combined with phenothiazine antipsychotics (9). Although EPO does not have intrinsic estrogenic properties, several manufacturers do combine EPO with phytoestrogens, and product labels should be carefully reviewed.
Theoretically, GLA can be converted directly to the prostaglandin, precursor dihomo-GLA. The administration of the oil might be beneficial to individuals unable to metabolize cis-linolenic acid to GLA and to produce subsequent intermediates of considerable metabolic significance, including prostaglandins. (2)(3)
Repeated oral administration of evening primrose oil (480 mg/day gamma-linoleic acid/day) to health volunteers resulted in mean Cmax of approximately 20.7-22.6 mcg/ml. Gamma-linoleic acid levels were approximately 4.5 times greater from baseline in all patients, but serum levels of other fatty acids did not change significantly from baseline. Gastric absorption and Tmax for morning doses was longer than Tmax for identical doses given in the evening. (11)
Reported: Headache, GI upset, nausea, and increased risk of pregnancy complications Petechiae and ecchymoses were observed in a neonate whose mother used raspberry leaf tea and evening primrose oil (vaginally and orally) 1 week before childbirth. (12)
Anticoagulants / Antiplatelets: May have additive effects and increase risk of bleeding. Phenothiazines (e.g. fluphenazine): Evening primrose oil may lower the seizure threshold and precipitate seizures in patients taking phenothiazines. (9)
Budeiri D, et al. Is evening primrose oil of value in the treatment of premenstrual syndrome? Control Clin Trials 1996;17:60-8. A systematic literature search of clinical trials of evening primrose oil for the treatment of PMS was carried out with a view to performing a meta-analysis. Seven placebo-controlled trials were found, but in only five trials was randomization clearly indicated. The two well-controlled studies failed to show any beneficial effects for EPO, although modest effects cannot be excluded given that the trials were relatively small. Nonetheless, on current evidence, EPO is of little value in the management of premenstrual syndrome.
Srivastava A, et al. Evidence-based management of Mastalgia: a meta-analysis of randomised trials. Breast. Oct 2007;16(5):503-512. In a meta-analysis of commonly used treatments for mastalgia, including Evening primrose oil (EPO), Bromocriptine, Danazol, and Tamoxifen, previously reported randomized, placebo-controlled trials were analyzed. Three randomized, controlled trials of EPO were included along with 1 trial of gamma-linolenic acid. Although Bromocriptine, Danazol, and Tamoxifen improved mastalgia, EPO was ineffective and therefore should not be used for mastalgia relief.
