The trade in, and consumption of, illicit drugs is perhaps the archetypal ‘wicked problem’ of our time – complex, globalized, and seemingly intractable – and presents us with one of the very hardest legal and policy challenges of the twenty‐first century. The central concept of a ‘drug’ remains under‐theorized and largely neglected by critical socio‐legal and criminological scholars. Drawing on a range of primary archival material and secondary sources, this article sets out a genealogy of the concept, assembled a little over a century ago out of diverse lines of development. It is argued that the drug label is an invented legal‐regulatory construct closely bound up with the global drug prohibition system. Many contemporary features of the ‘war on drugs’ bear traces of this genealogy, notably how drug law enforcement often contributes to racial and social injustice. To move beyond prohibition, radical law and policy reform may require us to abandon the drug concept entirely.