FRS 1000, an extract of red onion peel, strongly inhibits phosphodiesterase 5A (PDE 5A).

As part of our ongoing search for flavonoids that are bioactive in humans, it was determined that FRS 1000, a beverage containing flavonoids extracted from onion peel, showed unexpected improvement of male sexual function. An in vitro enzyme assay clearly showed that FRS 1000 has a strong phosphodiesterase 5A (PDE 5A) inhibitory activity, which is considered to be important for treatment of erectile dysfunction. Detailed assays of each major ingredient indicated that the antioxidative flavonoid quercetin was responsible for the activity. Results also suggested that PDE 5A inhibition is not directly related to the free radical scavenging activity of flavonoids.