Phase IV of Clinical trial is done:

Ans. (d) Post marketing surveillanceRef.: K. Park 23rd ed. / 84-85Clinical TrialsPhaseSubjectsPurpose* Phase 1Healthy human volunteerSafety and non-toxicity* Phase 2Patients (20-200)Effectiveness* Phase 3PatientsComparison with existing drug* Phase 4PatientLong term side effects Post marketing surveillance* Most important phase of clinical trial: Phase 3* A new drug is launched in market after phase 3PHASE 4* Post marketing surveillance* Longest phase: 10-25 years* To study the long term side effects of a drug* Doesn't require ethical clearance.