Enhancement of exposure therapy in participants with specific phobia: A randomized controlled trial comparing yohimbine, propranolol and placebo

Background: Recent research indicates that pharmacological agents may enhance psychotherapeutic outcome. Yet, empirical results have not been conclusive with respect to two pharmacological agents, yohimbine hydrochloride (YOH) and propranolol. YOH is suggested to enhance emotional memory by elevating nor epinephrine, whereas the beta-adrenergic receptor antagonist propranolol might help better cope with feared situations by reducing accompanying bodily sensations. Methods: In this controlled trial, fifty-six participants with specific phobia were randomly assigned to either 1) virtual reality exposure therapy (VRET) plus YOH, 2) VRET plus Propranolol, or 3) VRET plus placebo. Participants in all conditions received three sessions of VRET over a period of two weeks. Results: We conducted 2 x 3 repeated measures MANOVA's. Results showed a significant effect for time, with partial eta squared ranging from eta p2 = 0.647 to eta p2 = 0.692, for specific phobia, yet no significant interaction effects were found. Conclusion: No significant differences were found when VRET with YOH or a beta-blocker was compared to VRET with a non-active placebo. Implications for clinical practice and future research are discussed.