Module 2: Basic Pharmacology of Controlled Drugs and Substances

Lesson 2

Methadone – Pharmacodynamics / mechanism of action

Methadone acts as a μ-opioid receptor agonist as well as an N-Methyl-D-aspartate (NMDA) receptor agonist, altering perception and response to painful stimuli.  When being used for opioid addiction management, methadone can prevent symptoms of withdrawal, decreases cravings for opioids, and blocks the sensation of euphoria. Physical symptoms of methadone ingestion include constricted pupils, decreased mobility of the GI tract, and decreased rate of respirations (Canadian Pharmacists Association, 2014). It is available in oral (syrup or tablets) and injectable forms.


  • Canadian Pharmacists Association. (2014). E-Therapeutics. Ottawa, ON: Author.