This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
Tolerance develops to all of the following actions of opioid except: 
Select and explain. 
A. Miosis, B. Analgesia, C. Euphoria, D. Nausea and vomiting
A: Miosis
Answer: A: Miosis 
Explanation: Ref: Katzung 11/e p539 Tolerance cannot develop to 3Cs *Constipation *Constriction of pupil *Convulsions