Evening primrose oil. Molecular model of gamma- linoleic acid (GLA). Molecules are represented as spheres and are colour-coded: carbon (purple), hydrogen (white) and oxygen (blue). This omega-6 essential fatty acid is found in the evening primrose plant and so is also known as evening primrose oil. It has many uses in herbal medicine, including relieving premenstrual tension, breast tenderness, eczema and controlling alcoholism. It has also been found to act on the same receptor in breast cancers as the drug herceptin. Supplementing with GLA may reduce cancer growth, kill tumour cells and enhance the efficacy of other breast cancer treatments. However, it has not been shown to provide any protection against the disease.