A single-nucleotide polymorphism in ADRA2A, rs553668A — which leads to overexpression of the α2A-adrenergic receptor (α2AAR) — has been associated with defective β cell function and increased risk of type 2 diabetes. Here, results of a randomized clinical study, in which 50 patients with type 2 diabetes were treated with the α2AAR antagonist yohimbine, are reported. The study met its primary end point, with yohimbine markedly increasing insulin secretion in risk allele carriers at 30 minutes during an oral-glucose tolerance test, to a level similar to that in non-risk allele carriers.