This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: RCT, Trials, Subject name: Social & Preventive Medicine
Efficacy of new drug A is compared with an existing drug B in: 
Select and explain. 
A. Clinical trial phase I, B. Clinical trial phase II, C. Clinical trial phase III, D. Clinical trial phase IV
C: Clinical trial phase III
Answer: C: Clinical trial phase III 
Explanation: Phase Unit of study Purpose PRECLINICAL PHASE Lab experiments Animals Pretesting CLINICAL PHASE Typical No. of patients Phase 0 Healthy human volunteers Micro - dosing Phase I Healthy human volunteers Safety and non - toxicity profile 10 to 30 usually healthy volunteers Phase II Patients Effectiveness Fewer than 100 Phase III Patients Comparison with existing drugs Hundreds or thousands Phase IV Patients Long term side effects Many thousands