This article evaluates the effect of a police crackdown on cannabis vendors operating in cryptomarkets. The police seized >100 cannabis parcels in transit and arrested one runner during this crackdown. An automated web crawler was used to download, and structure content found on 30 cryptomarkets between 1 January 2015 and 26 June 2017. Data were then aggregated on a weekly basis. The synthetic difference-and-difference (SDiD) approach and its extension for event-study analysis were used to estimate the effect of the police crackdown on the number of cannabis transactions and vendors. Estimates from the SDiD models suggest that the crackdown was associated with a significant decline in cannabis transactions. The event-study analysis indicates that the effect was delayed and for a short time. Estimates from the SDiD show that the overall effect of the crackdown on vendors was not significant. The event-study analysis shows that a significant effect was observed for several time units; the effect can be characterized as abrupt and lasted for several weeks after the intervention. Results suggest that police crackdowns can effectively disrupt for cryptomarkets. Seizing parcels negatively affected vendors' reputation and compromised the trust system on which cryptomarkets are built.