OBJECTIVE: To explore vital sign changes among patient subgroups during the 6-week lead-in period of the sibutramine cardiovascular outcomes (SCOUT) trial. METHODS: SCOUT is an ongoing, double-blind, randomized, placebo-controlled outcome trial in overweight/obese patients at high risk of a cardiovascular event. During the 6-week lead-in period, 10,742 patients received sibutramine and weight management. Vital sign changes were assessed post hoc by initial blood pressure (mmHg) categorized as normal (<130/<85), high-normal (130 to <140/85 to <90) or hypertensive (>or=140/>or=90); weight change categories (weight gain/no weight change, >0 to 2.5% weight loss, >2.5 to 5% weight loss and >5% weight loss) and current antihypertensive medication class use (none, one, or two or more). To assess the impact of sibutramine on blood pressure and pulse rate, only patients (N = 10,025) who reported no change in the class of antihypertensive medication used and who did not report an increase in antihypertensive medication use were analysed. RESULTS: At entry, approximately 50% of patients were hypertensive and 26% were high-normal. In hypertensive patients, blood pressure changes (mmHg) decreased by median [5th, 95th percentile] of -6.5 systolic [-27.0, 8.0] and -2.0 diastolic [-15.0, 8.0] (p < 0.001). Hypertensive patients with no weight loss or with weight gain had median decreases of -3.5 systolic [-26.0, 10.0] and -1.5 diastolic [-16.0, 9.0] (p < 0.001). Normotensive patients had median increases of 1.5 systolic [-15.0, 19.5] and 1.0 diastolic [-10.5, 13.0] (p < 0.001) attenuated with increasing weight loss. Approximately 43% of patients initially categorized as hypertensive had a lower blood pressure category at end-point. Concomitant antihypertensive medication classes did not affect blood pressure reductions. Pulse rates were uniformly elevated (median 1-4 bpm, p < 0.001) across blood pressure and weight change categories. CONCLUSIONS: In hypertensive patients (>or=140/>or=90), blood pressure decreases were observed during 6-week treatment with sibutramine even when body weight was unchanged. In patients with normal blood pressure (<130/<85), weight loss of >5% induced decreases in systolic blood pressure; otherwise, small increases were observed. Small pulse rate increases were observed regardless of blood pressure or weight change status.