Minoxidil-d10 contains 10 deuterium atoms on the piperidine ring. It is intended for use as an internal standard for the quantification of minoxidil by GC- or LC-mass spectrometry. Minoxidil is a pyrimidine derivative that was originally developed as an anti-hypertensive agent and unexpectedly found to stimulate hair growth. Minoxidil directly affects arteriolar smooth muscle to decrease vascular resistance in part by opening ATP-sensitive potassium channels. It can activate cyclooxygenase 1 (AC50 = 80 μM), which is expressed in the dermal papilla of hair follicles, increasing prostaglandin E2 production in BALB/c 3T3 fibroblasts and human dermal papilla fibroblasts.