Results of quantitative MRI-based regional GM volume/density in individuals, who purportedly depended on or abused primarily a single drug, have been inconsistent. Some cross-sectional studies reported smaller regional GM volumes/densities (predominantly in the frontal and temporal lobes, but also in thalamus) in both active and abstinent users of cocaine (Fein et al., 2002; Franklin et al., 2002; Lim et al., 2008; Sim et al., 2007), cannabis (Matochik et al., 2005; Yucel et al., 2008), methamphetamine (Berman et al., 2008; Thompson et al., 2004) and heroin (Yucel et al., 2008) compared to controls. Others reported larger GM volumes/densities in cocaine dependent individuals (Hanlon et al., 2011), cannabis abusers (Cousijn et al., 2012) and methamphetamine abusers (Jernigan et al., 2005) compared to controls; and yet others found no effects of chronic cannabis misuse on brain morphology (Block et al., 2000; Medina et al., 2009; Tzilos et al., 2005). On the other hand, while previous reports on the effects of PSUD on brain GM volumes are sparse, they are at least consistent: GM volumes were reduced compared to age-matched drug-free controls in prefrontal
