On a mental level, it fights stress and fatigue and increases energy, which is reflected in increased sexual drive and libido. This is another herb which is great for enhancing nitric oxide levels and also increases testosterone. The herb works just like Viagra to increase nitric oxide release in the blood vessels and inhibit PDE-5.Cnidium also helps promote better blood circulation throughout the whole body and is also a blood tonic. Avoid consuming any food or drinks that contain grapefruit before or while using Levitra or Viagra.