A controlled clinical trial of the cardiovascular and psychological effects of phenylpropanolamine and caffeine.

Two hundred eighty-eight healthy normotensive volunteers with various degrees of obesity participated in a double-blind, placebo-controlled evaluation of the acute effects of phenylpropanolamine hydrochloride (PPA) and caffeine on blood pressure, pulse, and subjective effects. Dosage forms studied were PPA 75 mg sustained-release (SR), PPA SR 75 mg with caffeine 200 mg, caffeine 200 mg, and placebo. Data analysis indicated no significant cardiovascular or subjective effects due to PPA. Caffeine, however, was associated with statistically reliable though clinically insignificant changes from baseline diastolic blood pressure in both supine and standing positions. The rank order of the change indicated larger increases for the subjects who received caffeine, either alone or in combination with PPA, as compared with those who received PPA alone or placebo. No statistically significant differences between PPA and placebo were observed. Subjects in the heavier weight categories had higher blood pressure levels throughout the session as compared with those of normal weight. There was no difference among the study groups in subjective effects. These results provide evidence supporting the safety of currently recommended doses of sustained-release PPA, either alone or in combination with small doses of caffeine in healthy individuals.