Tadalafil, a drug that seems to improve blood flow in skeletal muscle during exercise by boosting nitric oxide–cGMP signalling, has shown promise in preclinical models of Duchenne muscular dystrophy (DMD). However, a new phase III trial found little evidence of benefit in the clinic. The trial included 331 individuals with DMD aged 7–14 years, who were randomly assigned to receive 0.3 mg/kg or 0.6 mg/kg tadalafil or a placebo daily for 48 weeks. Participants were assessed on the 6-minute walk distance (6MWD) and the Performance of Upper Limb (PUL) test at baseline and at 12-week intervals. Tadalafil did not prevent a decline in performance on the 6MWD; however, the lower dose of the drug was associated with some stabilization of PUL scores in boys aged >10 years. The investigators suggest that the effects of tadalafil on upper limb function warrant further exploration.