Although preceding its association with substance use, early uses of the term ‘addiction’ signified intense attachment or ‘devotion’ to an activity or pursuit, indicating compromised autonomy, a necessary ‘culling’ of conflicting obligations, such as family and other concerns, and a potentially dangerous surrender (Lemon 2018). Recent advances in biomedical and neuroscientific understandings of addiction, as a relapsing neurological disorder, have sharpened notions of substance use as being outside of conscious control. Yet framing addiction in terms of individual, neurobiological predispositions towards addictive behaviour, continues to impact how we view agency, responsibility, and autonomy, even as substances are ascribed their own powerful agencies. Based on long-term ethnographic fieldwork with individuals and third sector services in south-east Scotland, this article attends to ambiguous notions of agency attributed to and by people who use substances, and to substances themselves. It asks how responsibility for recovery becomes divested onto individuals, and how a moral ‘devotion’ to one’s recovery is mandated by medical and judicial institutions. The article further highlights how dyadic and intimate relationships with heroin are emplaced within wider webs of relations, and how heroin itself is suffused with agency and intentionality: becoming at once a force for destruction and source of life-giving surrender.