Bitter Orange (Citrus aurantium) contains small amounts of alkaloids such as synephrine and octopamine, adrenergic agents with beta-agonist activity. These stimulate lipolysis and increase the resting metabolic rate in some people, thus increasing the removal and oxidation of fat from adipose tissue stores. This action is potentiated by methylxanthines, such as the caffeine present in Guarana (Paullinia cupana). Ginkgosides from Ginkgo biloba dilate blood vessels and improve peripheral and cerebral circulation. The ginsenosides present in Oriental Ginseng (Panax ginseng) have a tonic effect on metabolism.