Study Comparing the Effects of Sibutramine and Phentermine on Psychomotor Performance

Abstract

Pharmacotherapy plays an important role in the management of obesity. At

present two drugs which act centrally are registered in Thailand; namely, sibutramine

and phentermine. In this study, the objective was to compare the effects of sibutramine

15 mg with phentermine 15 mg and placebo on psychomotor performance in Thai

healthy volunteers. A double blind, crossover studies with one week wash out interval

was performed in 20 Thai healthy volunteers aged between 18-65 years. During each

treatment psychomotor speed tests of warned and unwarned simple reaction time

(SRT) of visual, auditory and tactile types were measured. Phentermine shortened both

warned and unwarned simple reaction time (visual and auditory but not tactile simple

reaction time) significantly than sibutramine and placebo. Phentermine also

significantly increased diastolic blood pressure and pulse rate. These effects were also

related to the peak plasma concentration of orally extended release phentermine and

sibutramine. Adverse reactions including palpitation and insomnia were reported by

75% of subjects in phentermine-treated group and 40% in sibutramine-treated group.

This study indicated that phentermine acts as a CNS stimulant and may result in the

increase in blood pressure and pulse rate, while sibutramine produced much less

stimulating effects on the CNS and cardiovascular systems than phentermine.