Background: Epidemiologic analysis of family data on blood pressure (BP) is often compromised by the effects of antihypertensive medications. A review of numerous clinical trials that investigated the effects of BP-lowering medications is summarized here. Methods: Published clinical trials, including 137 clinical trials with monodrug therapies and 28 clinical trials of combination drug therapies with a total of 11,739 participants, were reviewed from PubMed. Six major classes/groups of antihypertensive medications were categorized by ethnicity, including angiotensin-converting enzyme (ACE) inhibitors, α1-blockers, cardioselective β-blockers (β1-blockers), calcium channel blockers, thiazide and thiazide-like diuretics, and loop diuretics. Results: Using sitting or supine BP, for ethnic groups combined, monodrug therapy with ACE inhibitors showed a weighted average effect of lowering the systolic and diastolic BP by 12.5/9.5 mm Hg; α1-blockers by 15.5/11.7 mm Hg; β1- blockers by 14.8/12.2 mm Hg; calcium channel blockers by 15.3/10.5 mm Hg; thiazide diuretics by 15.3/9.8 mm Hg; and loop diuretics by 15.8/8.2 mm Hg. However, ACE inhibitors, α1-blockers, and β1- blockers were less effective in African Americans than in non-African Americans, whereas calcium channel blockers, thiazide diuretics, and loop diuretics were more effective in African Americans than in non-African Americans. For two-drug combination therapy with ethnic groups combined, the BP-lowering effect of the second medication, when compared to its effect as monodrug therapy, was 84% and 65% for systolic and diastolic BP, respectively. Conclusions: The BP-lowering effects reported here may be used to impute the pretreatment BP levels, which can improve the information content and hence the power of epidemiologic analysis in studies where use of antihypertensive medications is a confounding factor in the BP measurements. © 2005 American Journal of Hypertension, Ltd.