 If phase 1 testing is successful, potential new treatments go on to larger phase 2 studies which are designed to further assess risks and also to evaluate whether there is any evidence that the treatment might be beneficial. Successful phase 2 studies are followed by phase 3 studies which involve hundreds, sometimes thousands of patients. Phase 3 studies are designed to provide a rigorous test of the efficacy of a treatment and frequently involve randomization of participants to the new treatment or a control, which might be the current treatment or a placebo. Finally, post-marketing or phase 4 studies evaluate the use of interventions in clinical practice.