The authors treated 19 depressive inpatients double-blind with a mean
dose of 78 mg/day of phenelzine for 3 weeks to determine the possible
relationship between monoamine oxidase (MAO) inhibition and the
effectiveness of phenelzine. Clinical ratings made on the Hamilton
Depression Rating Scale, the Beck Depression Inventory, and the SCL-90
indicated a minimum of 60% MAO inhibition had to be achieved for the drug
to be consistently beneficial.