FOSB and drug dependence: Levels of FosB mRNA expression in PBLs may represent a peripheral marker for molecular changes in substance use disorders and could be useful to follow the after effects of drug dependence treatment, especially those that potentially modify synaptic plasticity such as non-invasive brain stimulation (Cirillo et al., 2017), which has shown to decrease craving and relapses to the drug use (Klauss et al., 2014; Batista et al., 2015).