We undertook a single centre, randomized, controlled, double-blinded, crossover trial to determine the effect of North American ginseng (NAG) on 24-hour BP and renal function. After a 4-week placebo run-in, we randomly assigned participants to NAG or placebo treatment for 12-weeks at a dose of 3g/day. This was followed by an 8-week washout, and a subsequent 12-week period in which the opposite treatment was consumed. At run-in, and at weeks 0 and 12 of each treatment period, participants were fitted with an ambulatory BP monitor to assess 24-hour BP and serum cystatin C was measured.