The challenges of operating within the planet's carrying capacity call for an urgent transition towards sustainable consumption and production (Sustainable Development Goal 12). Despite the growing literature on sustainability transitions policies, the role of regulatory instruments has received limited attention. We conduct a qualitative content analysis and combine theoretical approaches on intervention points and the roles of law to study how regulatory instruments affect the transitions. The combined approach is applied to the European Union's Ecodesign Directive and two product groups regulated under this framework, washing machines and lighting. The results shed light on two transition processes: the evolution of product design towards energy efficiency and then towards circularity. Ecodesign has so far steered and accelerated the transition towards energy efficiency with harmonised minimum requirements and bans as the regulatory spearhead. The requirements have stimulated and accelerated niches and destabilised the unsustainable incumbent regime in product design. Yet, the requirements' long processes, narrowing assumptions on future developments and difficulties in managing the broader effects have also held the transition back. The recent introduction of circularity-related requirements aims at destabilising the prevailing linear regime, even at shifting the broader landscape of production and consumption. However, the transition towards the circular economy is decelerated by the ensuing, complicated trade-offs and broader repercussions that are difficult to anticipate. The paper thus shows how the role of regulatory instruments in transitions is considerably more complicated than is generally realised. We conclude that the combined analytical approach is useful for better understanding the nuances and intricacies in sustainability transitions. The study highlights how the governance of sustainability transitions towards a more circular economy with regulatory instruments must be comprehensive yet granular: the policymakers need to carefully and systematically consider the steering, accelerating as well as braking roles for all points of intervention.