A study arm refers to a group of participants in a clinical trial who receive a specific treatment or intervention (including placebo or no intervention) according to the schedule defined in the protocol. Randomized controlled trials have at least two arms: an investigational arm (receiving the new drug) and a control arm (receiving a placebo or standard treatment). More complex designs may include multiple treatment arms with different doses or drug combinations.
A clear definition of the study arms is a fundamental aspect of study design and is described in detail in the protocol. Patients are typically assigned to the different arms through a randomization process to avoid selection bias. For CROs, managing study arms is critical for logistics (e.g., drug supply via IWRS systems) and for statistical analysis, in which outcomes are compared between arms to assess the efficacy and safety of the investigational medicinal product.