Evening Primrose Oil (EPO) is an extract of the Evening Primrose flower. Evening Primrose Oil (EPO) contains Gamma Linolenic acid (GLA), an essential fatty acid that gets converted into a hormone-like substance called prostaglandin E1. Evening Primrose Oil is a tiny, short-lived, bright yellow wildflower native to North America. After discovering this New World plant, the Europeans took it back to the Old World where its healing properties for ....