This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CLINICAL TRIALS, DRUG LABEL, Subject name: Pharmacology
Efficacy of new drug is confirmed in which phase? 
Select and explain. 
A. Phase -1, B. Phase-2, C. Phase-3, D. Phase-4
C: Phase-3
Answer: C: Phase-3 
Explanation: Clinical trials are divided into 4 phases: Phase I Done in healthy people - To know:- Max. tolerable dose (MTD) > Dosing >PK >Safety Phase II Done in 20-200 patients- To determine efficacy (first time) and safety Phase III Done in large no of patient upto 5000 (Multi centric)- to confirm efficacy and safety Phase IV Post marketing study - Rare/Long term side effects