In response to the HIV/AIDS and drug epidemic in China, the state-run Methadone Maintenance Treatment (MMT) program provides long-term to life-long replacement/maintenance therapy for drug users. The MMT program posits that methadone, a synthetic opioid, is a healthier alternative with fewer side effects compared to the highly addictive and destructive heroin. However, my ethnographic fieldwork conducted in the Guizhou and Yunnan provinces of Southwest China shows that users have diverse and contradictory bodily experiences and contested narratives regarding the impacts of these substances on their bodies and health. By adopting "local biologies" as the analytical framework, this study explores the sociopolitical processes through which embodied differences are created. It also reveals how drug users navigate their "unhealthy" experiences to redefine their relationships with different substances, to strive for moral legitimacy, and ultimately to concretize their often abstract and invisible lives. This study sheds light on how health is understood and experienced among a highly stigmatized and socially excluded population.