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 opioids except? 
Select and explain. 
A. Miosis, B. Analgesia, C. Euphoria, D. Nausea and vomiting
A: Miosis
Answer: A: Miosis 
Explanation: Repeated administration of morphine results in the development of tolerance to some of its effects including respiratory depression,analgesia, sedation and euphoriant effects and other CNS depressant effects. Constipation and miosis shows no tolerance Ref: KD Tripathi 8th ed.