OPRM1 and cocaine dependence: In cocaine addiction, higher levels of MOR availability are related to relapse and levels may reduce over time (Ghitza et al, 2010; Gorelick et al, 2008; Zubieta et al, 1996), though no changes in availability have been reported in alcoholism up to 3 months of sobriety (Heinz et al, 2005; Williams et al, 2009).