By design , three levels of BP reductions were achieved , adjusted mean BP reductions of 3.5 / 1.7 mm Hg ( P < 0.001 ) by aliskiren , 6.8 / 3.3 mm Hg ( P < 0.001 ) by hydrochlorothiazide or amlodipine , and 10.3 / 5.0 mm Hg ( P < 0.001 ) by double therapy compared with placebo .