BACKGROUND The use of the decongestant pseudoephedrine has been avoided in hypertensive patients with little evidence to support this caution. The purpose of this study was to determine the effects of therapeutic doses of pseudoephedrine on blood pressure in patients with controlled hypertension. METHODS Twenty-five patients with controlled hypertension were enrolled in a randomized, placebo-controlled, double-blind crossover trial. This was a 4-week study in which all participants received placebo during the 1st and 3rd weeks. Subjects were randomly assigned to receive pseudoephedrine or placebo during the 2nd week of the study, and to receive the opposite during the 4th week of the study. Blood pressure readings were taken at the beginning and end of each week of the trial, and at a 1-week poststudy follow-up visit. RESULTS The mean systolic pressure was 133 mm Hg in patients receiving both pseudoephedrine and placebo (P = NS). The mean diastolic pressure was 82 mm Hg in patients receiving pseudoephedrine and 82.5 mm Hg in patients receiving placebo. Mean pulse rates were 76.8 and 75.2 beats per minute in patients given pseudoephedrine and those given placebo, respectively (P = NS). There were no statistically significant or clinically important differences in the mean systolic or mean diastolic blood pressures among the groups during the entire 4-week course of the study. CONCLUSIONS At standard doses, pseudoephedrine has no significant effect on systolic or diastolic blood pressure in patients with controlled hypertension.