Phase II clinical trials are the second step in determining if a new medication is safe and effective. The main purpose of a Phase II clinical trial is to begin to assess whether a drug is effective while exposing as few people as possible to any unwanted side effects. Thus, the safe dosage levels that were estimated by the Phase I trial are used on a larger group of people, typically with study populations that range from about 100 to 300 people. All study participants will have been diagnosed with the condition that the new medication has been designed to treat. Phase II trials are used to see if a Phase III trial, a larger trial designed to prove effectiveness, is warranted. Phase II trials serve the purpose of screening out ineffective drugs with a minimum of expense and risk.