On the psychotropic effects of carbon dioxide.

It has been well established that the inhalation of Carbon Dioxide (CO2) can induce in humans an emotion closely replicating spontaneous panic attacks, as defined by current psychiatry nosology. The purpose of this review is to provide a critical summary of the data regarding CO2's psychopharmacological properties and underlying mechanisms. The authors review the literature on the human and animal response for the exposure of exogenous CO2 focusing on five points of interest: 1) the early history of the use of CO2 as an anesthetic and therapeutic agent, 2) the subjective effects of breathing CO2 at different concentrations in humans, 3) the use of CO2 in experimental psychiatric research as an experimental model of panic, 4) the pharmacological modulation of CO2-induced responses, and 5) the putative neurobiological mechanisms underlying the affective state induced by CO2. The authors conclude with an evolutionary-inspired notion that CO2 might act as an agent of a primal emotion serving a homeostatic function, in the control of respiration and acid-base balance.