One study has proven the effectiveness of evening primrose oil for menopause, reports WebMD. The study results showed a particular product with the ingredients evening primrose oil, ginseng, damiana and royal jelly reduced hot flashes and night sweats. However, most research indicates that the oil does not reduce menopause symptoms.
As of 2015, the evidence shows that taking a daily dose of evening primrose oil orally for three to six months, either with other supplements or by itself, does not reduce menopause-related night sweats or hot flashes, according to WebMD. It is likely safe for most people to use evening primrose oil for up to one year. Nausea, diarrhea and headaches are mild side effects that occur occasionally.