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Safety of evening primrose oil for breast cancer patients

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Ellen Sweeney, RD
Last Modified: July 14, 2002

Dear OncoLink "Ask The Experts,"
I had stage I breast cancer last year. I am presently on tamoxifen, and of course I began hot flashes and night sweats. I am premenopausal. My surgeon recommended I take evening primrose oil for the hot flashes, which works great. However, I'm getting conflicted reports lately that primrose oil has estrogen in it. Knowing the tamoxifen blocks estrogen, I shouldn't' be taking something that is estrogen. Can you tell me whether I should be taking primrose oil?  

Ellen Sweeney, RD, Clinical Nutrition Specialist Abramson Cancer Center of the University of Pennsylvania, responds:

Most herbals and supplements commonly used for relief of menopausal symptoms, or those symptoms commonly associated with tamoxifen use have been shown to have estrogen like properties (Dong Quai, Black Cohosh and soy). Evening primrose oil, however, has not been shown to have estrogen like effects. Its main compound that provides possible anti-inflammatory effect is gamma linolenic acids. Studies have shown evening primrose oil to be possibly effective in reducing mastalgia and PMS symptoms but effectiveness with relieving hot flashes has not been clearly shown. So, from an estrogen standpoint, it seems safe to take with Tamoxifen. Known drug interactions with evening primrose oil are anticoagulants, general anesthetics, and phenothiazines.