Stigmatizing attitudes toward people with a drug addiction have detrimental effects on the lives of these people. However, the factors that influence stigma toward people with a drug addiction have not yet been thoroughly investigated, compared with the stigma of other mental illnesses. Based on attribution theory, our experiment examined to what extent individual and contextual characteristics of people with a drug addiction influence stigmatizing attitudes toward people with a drug addiction. Moreover, we explored whether respondent characteristics indicative of familiarity with addiction decrease stigma toward people with a drug addiction.We conducted a full factorial survey of 2,857 respondents from a German online access panel who were from all walks of life. We experimentally varied vignettes (29-design) that featured a fictional person with an addiction. Stigmatizing beliefs, such as blame or fear, were assessed using the Attribution Questionnaire (AQ-9).Different attributes of people with a drug addiction and of the characteristics of their addiction modulated stigma in ways that are mostly consistent with attribution theory and related research. For example, female gender and younger age of people with a drug addiction diminished several stigmatizing attitudes; greater duration of addiction and social influence to use drugs increased them. Furthermore, characteristics of respondents modulated stigma: women, younger respondents, and those with higher education expressed less-stigmatizing responses than others.The stigmatization of people with a drug addiction is influenced by several factors, including characteristics of the stigmatized person, the addiction, and the person holding stigmatizing attitudes. A better understanding of the underlying mechanisms of these effects is needed to develop evidence-based antistigma measures.