NOW's Black Currant Oil 500 mg is commonly used to reduce inflammation. boost the immune system and promote detox. Oil from black currant seeds contains gamma-linolenic acid (GLA). a chemical that helps the immune system fight disease. The black current formulation produced by NOW contains 14 percent GLA. nearly double the content of that chemical found in Evening Primrose Oil. Black currant oil is used to help with arthritis. coughs. colds and more.