This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Phase 4 clinical trial 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 diseases, D. For drugs used in pediatric patients
B: After a drug is marketed
Answer: B: After a drug is marketed 
Explanation: Ans. is 'b' i.e., After a drug is marketed Phase 4 clinical trial is post marketing survellance.