Evening primrose oil does not contain estrogen. It does contain a fatty acid called gamma-linolenic acid (GLA), which may be associated with hormone-related effects as GLA can be converted in the body to a type of prostaglandin (a hormone-like substance).
Some people may use evening primrose oil to alleviate symptoms associated with hormonal imbalances, including menopausal symptoms. However, there is no conclusive medical proof. If you have concerns about hormonal balance, consult a professional.