JTT-654 is an orally active, potent and selective11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) inhibitor. The IC₅₀ of JTT-654 for 11β-HSD1 is 4.65, 0.97, and 0.74 nM in human, rat, and mouse recombinant enzymes, respectively. JTT-654 showed competitive inhibition against human recombinant enzyme. The IC₅₀ value for human 11β-HSD2 is > 30 μM (human 11β-HSD2 is responsible for the reverse reaction against human 11β-HSD1). JTT-654 ameliorates insulin resistance and non-obese type 2 diabetes by inhibiting adipose tissue and liver 11β-HSD1^[1][2].