The oil obtained from the evening primrose (Oenothera biennis) plant is usually taken orally in a gel cap form. This herbal supplement is most commonly used for the treatment of mastalgia and atopic dermatitis. While recommending this supplement to patients for many years for the treatment of mastalgia, this author was interested in researching the plant and the evidence supporting its use for this complaint and its other potential uses. The oil is rich in omega-6 fatty acids, which are essential for many bodily functions; however, a lack of strong scientific evidence exists to support its use for the relief of mastalgia or atopic dermatitis.