Metandienone, also known as 17α-methyl-δ1-testosterone or as 17α-methylandrost-1,4-dien-17β-ol-3-one, is a synthetic androstane steroid and a 17α-alkylated derivative of testosterone. It is a modification of testosterone with a methyl group at the C17α position and an additional double bond between the C1 and C2 positions. The drug is also the 17α-methylated derivative of boldenone (δ1-testosterone) and the δ1 analogue of methyltestosterone (17α-methyltestosterone).