Drug addiction has been associated with structural brain changes, but do they precede addiction or are they the consequence of it? Here, the authors showed that compared with unrelated healthy controls, stimulant-dependent individuals and their biological siblings have impaired inhibitory control, reduced white matter integrity in the prefrontal lobe and altered grey matter volume. These findings suggest that structural brain abnormalities may predispose individuals to reduced self-control, which, in the absence of resilience factors, may lead to stimulant addiction.