Absinthin's (1) complex structure is classified as a sesquiterpene lactone, meaning it belongs to a large category of natural products chemically derived from 5-carbon "building blocks" (3) derived from isoprene (4). The complete structure consists of two identical monomers (2) that are attached via a suspected naturally occurring Diels Alder reaction occurring at the alkenes on the 5-membered ring of the guaianolide.