Phase II

The second stage of clinical trials that tests the biological activity or effect of a drug in a larger group of 50-300 individuals. It assesses the drug’s efficacy and continues the safety assessments from Phase I. The trials are often divided into Phase IIa (dose-finding studies) and Phase IIb (proof of concept studies). These trials can be designed as case series or randomized controlled trials. The goal is to determine whether the drug influences the disease and has a broad effect in the patient population. Historically, Phase II studies have the lowest success rate among the development phases (nearly one third).

Source: Wikipedia