Background: Naltrexone (NTX) is an opioid antagonist indicated for the treatment of alcoholism, which is not universally effective. Thus, identifying individual predictors of NTX’s behavioral effects is critical to optimizing its therapeutic use. Moreover, given the high rate of relapse during treatment for alcoholism, understanding NTX’s behavioral effects when combined with moderate ethanol intake is important. Our previous study of abstinent alcoholics and control subjects showed that a more internal Locus of Control score predicted increased impulsive choice on NTX (Mitchell et al., 2007, Neuropsychopharmacology 32:439–449). Here, we tested whether this predictive relationship remains in the context of moderate alcohol intake.
Methods: In this study, we tested the effect of acute NTX (50 mg) on impulsive choice, motor inhibition, and attentional bias after ingestion of moderate ethanol (∼0.3 g/kg, n = 30 subjects). Subjects included those recruited from a pool of ∼1,200 UC Berkeley undergraduates on the basis of scores on the Barratt Impulsiveness Scale (BIS).
Results: Impulsive choice was positively correlated with breath alcohol concentration in placebo sessions. Locus of Control was again the sole predictor of NTX’s effect on decision making among subjects with a family history of alcoholism. We also found a weak interaction between BIS scores and NTX’s effect on impulsive choice.
Conclusions: Our results reinforce the predictive relationship between Locus of Control and NTX’s effect on decision making in those with a family history of alcoholism, suggesting a possible biological basis to this relationship.