One of the key motives behind recent reforms of the EU's legislative process has been to increase efficiency. This study examines whether the Amsterdam, Nice and Lisbon treaties have successfully increased the speed with which the EU creates new laws. An interrupted time series approach is utilized to detect the total effects of treaty change on the decision‐making process. This study thus complements existing research on the effects of decision‐making rules, by employing a design more robust to the challenge of endogeneity. The findings suggest that the Amsterdam treaty was very successful at increasing legislative efficiency. In contrast, the Nice treaty does not appear to have had a notable impact, and, more interestingly, neither does the Lisbon treaty.