The oil of the Evening Primrose seed is a rich source of cis-g-linolenic acid (GLA). GLA is a precursor of a hormone-like substance called PGE1 which has a wide range of Sona Evening Primrose Oil 500mg capsules are made with the highest quality, cold pressed oil, with a Guaranteed 10% GLA (Gamma Linolenic Acid, an omega 6 fatty acid) as well as linoleic acid and oleic acid. Each capsule also contains natural vitamin E which is an essential vitamin and anti-oxidant to protect cells against oxidative stress/damage.