Caryophyllene is a natural bicyclic sesquiterpene that is a constituent of many essential oils, especially clove oil, the oil from the stems and flowers of Syzygium aromaticum (cloves), the essential oil of hemp Cannabis sativa, rosemary Rosmarinus oficinalis, and hops. It is usually found as a mixture with isocaryophyllene (the cis double bond isomer) and α-humulene (obsolete name: α-caryophyllene), a ring-opened isomer. Caryophyllene is notable for having a cyclobutane ring, a rarity in nature. Caryophyllene is one of the chemical compounds that contributes to the spiciness of black pepper. In a study conducted by Jürg Gertsch et al. from the Swiss Federal Institute of Technology (ETH Zurich), beta-caryophyllene was shown to be selective agonist of cannabinoid receptor type-2 (CB2) and to exert significant cannabimimetic antiinflammatory effects in mice.