Despite the well established efficacy of naltrexone, there are significant variations in individual responses to naltrexone. A critical question remains: under what circumstances and for which patients will naltrexone (NTX) be most beneficial? Recent work at our center provides evidence that the mu-opioid receptor (OPRM1) gene polymorphism A118G (Asn40Asp) imparts a significant change in treatment response. We have shown that patients with 1-2 copies of the Asp40 variant have significantly better treatment responses than patients with Asn40 variant (absence of heavy drinking -73.9% v/s 49% response). To further consolidate our knowledge, we wish to test the relationship between A118G polymorphism and the response to treatment with naltrexone. This work is focused on subjects of European or Asian descent as the A118G polymorphism occurs in less than 1% of those of African descent.