Evening primrose (Oenothera biennis) is a wildflower native to North America but now grown in at least 30 countries. Oil is pressed from its seeds. Evening primrose oil has been used to treat premenstrual syndrome (PMS) and many other conditions, including eczema and rheumatoid arthritis, but the results of studies of its effectiveness have been conflicting.

The oil made from its seeds is a source of gamma linolenic acid (GLA), an omega-6 fatty acid. GLA has been reported to lower the seizure threshold (which would make seizures more likely), but some studies with animals have found an antiseizure effect from fatty acids.

Evening primrose oil may interact with other medications, including a type called phenothiazines, which are used to treat psychiatric disorders. Examples of phenothiazines include Thorazine (chlorpromazine) and Mellaril (thioridazine). Seizures can result from using these substances together.

Read more about evening primrose oil in the "About Herbs" section of the Memorial Sloan-Kettering Cancer Center website. (If you have not visited the site before, the information on evening primrose oil will be preceded by a Disclaimer.)

Much of the information in this article is based on Spinella M: Herbal medicines and epilepsy: The potential for benefit and adverse effects. Epilepsy Behav 2001; 2(6):524-532. (PMID 12609386)

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed:12/15/06