Anxiogenic properties of yohimbine. II. Influence of experimental set and setting.

To study the pharmacological induction of stress along with psychological stress and their possible interaction, 20 mg yohimbine and placebo orally were administered to 8 panic patients on placebo treatment, 7 panic patients on alprazolam treatment and 12 controls in a double-blind crossover design. Two structured situations which can be considered as 'neutral' stressors were included: a mental arithmetic task and a continuous performance task. Mental arithmetic induced robust increases in ratings of panicky, anxiety, nervousness, heart rate and electrodermal activity, while the continuous performance task induced increases exclusively in skin conductance reaction. Patients responded to these tasks less than controls with regard to subjective ratings and electrodermal activity. Yohimbine did not potentiate the response to the tasks in the patients. In controls, heart rate during the mental arithmetic task, but not during rest, was increased after yohimbine. In contrast to other yohimbine challenge studies no panic attacks were observed. It is hypothesized that the experimental design together with an instructional set that reduces expectancy factors and the inclusion of structured and time-limited tasks in a challenge paradigm is able to reduce the anxiogenic effects of yohimbine.