Mespirenone (INN) (developmental code name ZK-94679), also known as Δ¹-15β,16β-methylenespironolactone, is a steroidal antimineralocorticoid of the spirolactone group related to spironolactone that was never marketed. Animal research found that it was 3.3-fold more potent as an antimineralocorticoid relative to spironolactone. In addition to its antimineralocorticoid properties, mespirenone is also a progestogen, antigonadotropin, and antiandrogen. It is 2- to 3-fold as potent as spironolactone as a progestogen and antigonadotropin but its antiandrogenic activity is markedly reduced and weak (though still of significance) in comparison. Mespirenone is also a potent and specific enzyme inhibitor of 18-hydroxylase and thus of mineralocorticoid biosynthesis. The drug was under development by Schering (now Bayer Schering Pharma) and reached phase II clinical trials but was discontinued in 1989.