EPO is a rich source of the long-chain fatty acid gamma-linolenic acid (GLA). The health benefits of EPO are attributed to GLA. GLA is an unusual constituent of living matter and is found in very few plants. These include, in addition to evening primrose, black currant, borage and hemp. GLA content in EPO ranges from approximately 7 to 14%. Typical EPO supplements contain about 9% and 10% GLA.