This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Pharmacology
A patient presented with pain in the right lower quadrant of abdomen. He has history of renal stones in right kidney. He was prescribed an opioid which is agonist at kappa receptors and antagonist at mu receptors. The likely drug given was: 
Select and explain. 
A. Pentazocine, B. Buprenorphine, C. Tramadol, D. Fentanyl
A: Pentazocine
Answer: A: Pentazocine 
Explanation: Kappa agonist and mu antagonist are:Pentazocine, nalbuphine, butarphanol.They are responsible for causing dysphoria as a side effect.Buprenorphine is paial mu agonist and kappa antagonist.Tramadol and fentanyl are synthetic opioids.