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
Phase 4 clinical trials is carried out: 
Select and explain. 
A. Before the marketing approval of a drug, B. After a drug is marketed, C. For drugs used in rare disease, D. For drugs used in pediatric patients
B: After a drug is marketed
Answer: B: After a drug is marketed 
Explanation: A new drug/ vaccine is launched in the market after phase III (RCT). Phase IV is 'Post marketing surveillance phase' Is the longest phase in a clinical trial. Should be carried out life long (minimum 10-25 years). Is done for finding 'long term side effects and rare side effects' of the drug.