Subjects will attend the clinical research unit on days 1, 2, 3, 4 and 5 to monitor safety and tolerability for both drugs. Subjects will attend the clinical unit on days 4 and 5 for a two day assessment, using a series of pharmacodynamic measurements known to be sensitive to the effects of GSK1521498 and/or NTX: Functional brain response to alcohol and food cues; plasma cortisol; hedonic and consummatory eating behaviors; subjective response to an ethanol challenge; experimental pain threshold; and cognitive tests of attention bias towards alcohol and food cues.