Antidepressant efficacy of tranylcypromine isomers: a controlled study.

The (+)- and (-)-isomers of the monoamine oxidase inhibitor (MAO-I) tranylcypromine (TCP) were administered separately in a double-blind controlled study to 20 depressed patients. The Hamilton Depression Rating Scale, the AMP-system and the Bf-s self-rating questionnaire were used for documentation of psychopathological state and autonomic side effects. Overall there was a statistically significant decrease in the Hamilton depression scores (p less than 0.01 for the (+)-isomer, but not for the (-)-isomer group, whereas self-rating scores did not show a significant decrease in either group. Autonomic side effects were more pronounced (p less than 0.05) in the (+)-isomer group. As platelet MAO was significantly stronger (p less than 0.001) inhibited in the (+)-TCP group as compared with the (-)-TCP group, it is suggested that MAO inhibition rather than uptake blockade is the biochemical mechanism responsible for both the antidepressant activity and the autonomic side effects due to TCP medication.