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We evaluate the impact on hospital admissions related to illicit drug use, caused by a policing experiment that depenalized the possession of small quantities of cannabis in the London borough of Lambeth. We exploit administrative records on individual hospital ad missions and with ICD-10 diagnosis classications. We use these records to construct a panel data set by London borough and quarter from 1997 to 2009 to estimate the short and long run impacts of the depenalization policy unilaterally introduced into Lambeth between 2001 and 2002. We nd the depenalization of cannabis had signicant longer term impacts on hospital admissions related to the use of hard drugs. Among Lambeth residents, the impacts are concentrated among men, and are proportionately larger in younger cohorts, and among those with prior histories of hospitalization related to drug or alcohol use. The magnitudes of the impacts are large, corresponding to between 33% and 64% of baseline admission rates across age cohorts. The dynamic impacts across cohorts vary in prole with some cohorts experiencing hospitalization rates remaining above pre-intervention levels six years after the depenalization of cannabis was rst introduced. We nd evidence of positive spillover effects in hospitalization rates related to hard drugs among those resident in boroughs neighboring Lambeth, and these are concentrated among cohorts without prior histories of hospitalizations related to the use of illicit drugs or alcohol. Finally, the severity of hospital admissions, as measured by the length of hospital stays, signicantly increases for admissions related to the use of hard drugs and cannabis. Overall, our results suggest policing strategies related to the cannabis market have signicant, nuanced and lasting impacts on public health.

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