A double dose of phenylpropanolamine causes transient hypertension

Phenylpropanolamine is widely used and freely available without a doctor's prescription in drug and grocery stores; it is the active ingredient in most diet aids and many cold preparations. Several cases of multiple cerebral hemorrhages associated with transient hypertension have recently been attributed to phenylpropanolamine in dosages equal to or less than that contained in two diet aids (i.e., 150 mg). Some evidence also exists on the additive effects of the co-ingestion of phenylpropanolamine and caffeine. We therefore undertook a study to demonstrate that a significant health risk can be caused by a double dose of a typical over-the-counter (OTC) diet aid (i.e., 150 mg phenylpropanolamine) and also when 75 mg phenylpropanolamine is taken with caffeine.

Five men and one woman, ranging in age from 20 to 30, participated in this study. The drug preparations were administered to each subject on different study days in a double-blind, randomized-crossover design. Identical capsules contained 75 mg sustained-release phenylpropanolamine, 400 mg of sustained-release caffeine, or placebo. Subjects ingested three capsules at the beginning of each study day. For 150 mg, two phenylpropanolamine-containing capsules and one placebo were taken; for 75 mg, one phenylpropanolamine capsule and two placebos; and for phenylpropanolamine plus caffeine, one 75 mg phenylpropanolamine capsule, one 400 mg caffeine capsule, and one placebo. Blood pressure and heart rate were monitored throughout the study.

Although 75 mg of phenylpropanolamine did not cause clinically relevant hypertension in our subjects, 150 mg of phenylpropanolamine and 75 mg of phenylpropanolamine plus 400 mg caffeine did result in significant blood pressure increases into the hypertensive range.

We believe that consumers often assume that double the recommended dosage of an OTC drug is safe and more effective. We suggest that requiring a physician's prescription or an additional, stronger warning label on phenylpropanolamine-containing products may prevent substantial mortality and morbidity.