Module 2: Basic Pharmacology of Controlled Drugs and Substances

Lesson 1

Opioids – Pharmacodynamics/mechanism of action

Opioids act primarily on receptors in the central nervous system (CNS) and intestines, and this is responsible for their analgesic effect. There are many subtypes of opioid receptors, but the three most commonly studied are mu (µ), delta (????) and kappa (К). Pure or full agonists include morphine, codeine, hydrocodone, oxycodone, hydromorphone, and fentanyl. These act mainly at the µ and К receptors (Canadian Pharmacists Association, 2014; Poole Arcangelo & Petersen, 2013).

The body has an endogenous opioid system in the brain where the natural-occurring opioid, β-endorphin, stimulates the µ receptors and produces a sensation of well-being and general anesthesia. Opioid medications are active at these same µ receptors leading to pain relief, relaxation, drowsiness, and euphoria. Desired and adverse effects are dose dependent and can include nausea, pupillary constriction, decreased urination, constipation, diaphoresis, itching, dry mouth, a suppressed cough reflex, respiratory depression, and even death (Canadian Pharmacists Association, 2014; Edmunds & Mayhew, 2014; Poole Arcangelo & Petersen, 2013).