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
Wof is true regarding tolerance occurring in regular opium abusers 
Select and explain. 
A. Tolerance develops to all actions of morphine, B. No tolerance occurs to euphoric and sedative actions of morphine, C. No tolerance occurs to constipating and miotic actions of morphine, D. Lethal dose of morphine is not significantly increased
C: No tolerance occurs to constipating and miotic actions of morphine
Answer: C: No tolerance occurs to constipating and miotic actions of morphine 
Explanation: Tolerance and dependence :- High degree of tolerance can be developed to morphine and related opioids if the drug is used repeatedly. It is paly pharmacokinetic (enhanced rate of metabolism), but mainly pharmacodynamic (cellular tolerance). Tolerance is exhibited to most actions, but not to constipating and miotic actions. Addicts tolerate morphine in grams: lethal dose is markedly increased. Ref:- kd tripathi; pg num:-473