Energy efficiency is a key component of energy policies worldwide. Corresponding measures tend to be considered in isolation and assessed by quantifying obtained energy savings. In contrast, so-called energy efficiency programmes can involve wider activity portfolios across sectors and usages, which present both operational complexities and synergies that are understudied. Accordingly, there is a lack of comprehensive tools for the monitoring and scaling of such programmes. This gap is addressed through participatory research within a regional, utility-led energy efficiency programme. Programme activities (e.g. subsidies) and effects (e.g. cost-effectiveness improvement) were inventoried from a round of workshops with programme staff, co-constructed with programme managers. They were then articulated into a system dynamics model, following a causality-mapping plenary workshop. This approach allows to assess and compare short- and long-term effects of otherwise incommensurable activities, as well as synergistic effects. Simulation results of this generic model suggest a significant long-term impact for learning and collaboration structures as well as networking activities, fostering actor engagement. Importantly, these activities have marginal, if at all quantifiable, short-term effects. Lastly, relevant activity component types (e.g. online subsidy application platform) were identified along the activity lifecycle. These components can be shared across activities to unlock synergistic potential. Key development principles are further suggested to achieve and enhance such synergies.