Glutamate and opioid systems play important roles in alcohol drinking behaviors. We examined if combined treatment with the NMDA antagonist memantine and the opioid antagonist naltrexone, when compared with naltrexone alone, would have a greater influence on alcohol drinking behaviors. Fifty-six, non-treatment-seeking heavy drinkers, with alcohol dependence and a positive family history (FHP) of alcoholism, participated in a randomized, double-blind, crossover trial, including two 6-8 days treatment periods, separated by a 6-day washout, and 3 alcohol drinking paradigm (ADP) sessions. After the first baseline (BAS) ADP1 session, participants were randomized to receive either naltrexone (NTX; 50 mg/day) + placebo memantine, or NTX (50 mg/day) + memantine (MEM; 20 mg/day), during the first treatment period, following which they completed ADP2. After a 6-day washout, participants were crossed over to the treatment they did not receive during the first treatment period, following which they completed ADP3. During each ADP, participants received a priming drink of alcohol followed by 3 1-hour, self-administration periods during which they had ad-lib access to 12 drinks. Individually, both NTX and NTX + MEM, when compared to BAS ADP1, significantly reduced the number of drinks consumed (p's < 0.001) and craving (p's < 0.001). When comparing NTX + MEM vs. NTX on number of drinks consumed, there was a significant treatment* sequence interaction (p = 0.004). Specifically, when NTX + MEM followed NTX alone, NTX + MEM resulted in a further reduction in drinking (mean: -1.94; 95% CI: -2.6, -0.8, p = 0.0005). However, when NTX alone followed NTX + MEM, NTX alone did not lead to further reduction in drinking (mean: 0.59; 95% CI: -0.67, 1.43, p = 0.47). Similar patterns were observed for alcohol craving; specifically, a significant reduction in craving was observed when NTX + MEM followed NTX alone (p = 0.009), but craving reduction was maintained when NTX + MEM was followed by NTX alone. Neither treatment condition significantly influenced alcohol-induced stimulation or sedation. Memantine (at a dose of 20 mg/day) enhances the efficacy of naltrexone (50 mg/day) in reducing alcohol drinking and craving among FHP drinkers with beneficial effects that appear to carryover after discontinuation of memantine treatment.