Effects of Metformin on Blood Pressure
Objective: To evaluate the effect of metformin on blood pressure and insulin sensitivity in non-diabetic, moderately obese, hypertensive patients.
Patients and Methods: An 8-week double-blind, placebo-controlled randomised study with a 4-week placebo run-in period was performed. Euglycaemic hyperinsulinaemic clamp tests and 24-hour ambulatory blood pressure measurements were performed after the 4-week placebo run-in period and after the 8-week double-blind treatment in patients in either the metformin 1500mg a day (n = 11) or corresponding placebo (n = 10) group.
Results: Metformin administration did not decrease either 24-hour ambulatory or office blood pressure when compared with placebo. The office mean systolic/diastolic (± standard deviation) blood pressures before and after treatments were 153 (± 22)/96 (± 4)mm Hg and 155 (± 14)/94 (± 6)mmHg in the metformin group, and 153 (± 30)/97 (± 9)mm Hg and 149 (± 18)/96 (± 9)mm Hg in the placebo group, respectively. Metformin significantly decreased fasting serum glucose concentrations from 5.7 (± 0.9) to 5.2 (± 0.4) mmol/L (p = 0.04), but did not affect the insulin sensitivity of the patients.
Conclusions: Metformin does not appear to have a place in the treatment of hypertension in non-diabetic individuals, at least in those with mild hypertension.

Insulin resistance is associated with essential hypertension, independent of obesity. Commonly used antihypertensive agents like




-adrenergic antagonists and thiazide diuretics do not usually decrease insulin resistance, and may even worsen it. In contrast, vasodilating antihypertensive agents, such as ACE-inhibitors, long-acting calcium antagonists and



₁-adrenoceptor antagonists, are neutral or improve insulin sensitivity.


Clinical experience has demonstrated that metformin, either alone or in combination with sulphonylureas, safely and effectively reduces hyperglycaemia in type 2 diabetes mellitus (non-insulin-dependent diabetes mellitus). Metformin probably inhibits hepatic glucose production and increases the sensitivity of peripheral tissues to insulin.

The association between insulin resistance and hypertension has prompted several studies on the use of metformin in the treatment of arterial hypertension. The results of these studies are, however, conflicting. In an open, uncontrolled pilot study, Landin et al.[15] reported that in non-diabetic, previously untreated hypertensive patients with normal bodyweight, metformin reduced blood pressure. At the same time, peripheral glucose uptake was increased, and circulating insulin and blood lipid levels were reduced. However, these investigators have later shown in a placebo-controlled, double-blind study that metformin treatment, despite some favourable metabolic effects, affected neither blood pressure nor glucose disposal rate in non-obese men. Giugliano et al. have reported that metformin may decrease blood pressure and increase insulin sensitivity in obese, non-diabetic, hypertensive women. The study by Snorgaard et al. concluded that metformin had only a minor and clinically insignificant effect on blood pressure in nondiabetic, hypertensive patients.

To clarify this conflicting situation, we performed an 8-week double-blind, placebo-controlled randomised study on the effect of metformin on blood pressure and insulin sensitivity in non-diabetic, moderately obese hypertensive patients.