This paper investigates the extent of polydrug use and recent polydrug trends among police detainees. Forty-one percent of detainees reported having used more than one illicit drug in the 30 days before detention. Fifty-nine percent of these used two drugs. The most common combination of polydrug use was cannabis and methamphetamine, and the proportion of detainees reporting this combination has more than doubled since 2009. Urinalysis data suggested that detainees under-reported polydrug use. The results indicate that more detainees may be at risk of the harms associated with polydrug use than survey data suggest.