Module 2: Basic Pharmacology of Controlled Drugs and Substances

Lesson 1

Barbiturates – Pharmacodynamics / mechanism of action

Similar to benzodiazepines, barbiturates’ main mechanism of action is their effect on the GABA receptor/chloride channel complex, and, specifically, the binding site of the receptor. Barbiturates have a greater effect on the chloride channel than benzodiazepines. Like benzodiazepines, however, they can cause tolerance as well as physical and psychological dependence, and their use has become limited to anesthetic and anti-epileptic indications. The pharmacodynamic effects of this class of drugs is dose dependent; small doses relieve tension whereas large doses produce drowsiness, staggering, blurred vision, impaired thinking, slurred speech, impaired perception of time and space, slowed reflexes and breathing, and reduced sensitivity to pain. Overdoses can cause unconsciousness, coma, and death. (Canadian Pharmacists Association, 2014).


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