Evening primrose oil is composed of linoleic acid and gamma linolenic acid and other fatty acids. Linoleic acid and gamma linolenic acid are classified as essential fatty acids.

Gamma linolenic acid (GLA) is made in the body, but It is not made enough before and after menstruation, not enough in menopause, and it increases cholesterol, disturbs physiological activity, and increase menstrual pain and breast pain. Hormone deficiency occurs before and after menstruation and menopause, where prostaglandin plays a substitute role, and gamma linolenic acid is the one that helps in the production of it.