The vulnerability to develop addiction to alcohol has been well established in familial and genetic studies. Similar familial and genetic studies have supported a vulnerability to drug addiction. The co-occurrence of alcohol and drug addiction in the same individuals is highly prevalent in clinical populations. Common putative neurochemical mechanisms underlie addiction to both alcohol and drugs, namely, in the mesolimbic pathway and the locus ceruleus in the brain. Treatment strategies are directed at both alcohol and multiple drug addictions in patient populations. The formulation of a generalized vulnerability that extends to both alcohol and drug addiction is not only possible but necessary to explain the substantial numbers of individuals who develop both alcohol and drug addictions. Future research that is pertinent and relevant may depend on the understanding of a generalized vulnerability to develop alcohol and drug addiction and its application in diagnostic strategies and treatment models.