T he incidence of diabetes mellitus and hypertension continues to rise worldwide. The proportion of patients with hypertension at risk for developing diabetes mellitus is also growing secondary to aging and increased obesity rates. 1 Several guidelines recommend thiazide diuretics as either first-line or add-on antihypertensive therapy to achieve blood pressure goals. 2 Concern over negative metabolic effects associated with thiazide diuretics, however, dates back Ͼ3 decades. 3 A substantial fraction of patients with hypertension have additional cardiovascular risk factors, and many have elevated fasting glucose and are at risk for developing diabetes mellitus. 4 Impaired fasting glucose itself increases the risk for cardiovascular events. 5 Any medication that worsens insulin sensitivity, ie, thiazide diuretics or most -blockers will hasten the development of diabetes mellitus in those with impaired fasting glucose. 6 Large observational studies demonstrate that thiazide diuretics and most -blockers increase the incidence of new-onset diabetes mellitus compared with renin-angiotensin system (RAS) blockers or calcium channel blockers. 7 To further support this observation, a network-based meta-analysis of hypertensive agents showed that RAS blockers were the agents least likely to be associated with the development of diabetes mellitus, whereas thiazides had a higher incidence of diabetes mellitus compared with placebo. 7 The mechanism traditionally associated with this increased risk of diuretic-associated diabetes mellitus is a reduction in serum potassium. A meta-analysis of 59 studies involving 83 thiazide diuretic treatment arms found a significant correlation between the degree of diureticinduced hypokalemia and an increase in plasma glucose. 8 Moreover, there is evidence that prevention of hypokalemia with K ϩ supplementation or potassium-sparing agents lessens the degree to which plasma glucose is increased consequent to diuretic therapy. 8 The mechanism of this glucose increase by diuretics may relate to insulin secretion. Mechanisms related to insulin release were reviewed recently, and it was noted that hyperkalemia stimulates insulin secretion and induces cellular uptake of potassium. 9 This suggests that low plasma potassium could impair insulin secretion and thereby increase plasma glucose. Ironically, the significant hypokalemia associated with hyperaldosteronism is not associated with hyperglycemia. The presence of insulin resistance and an impaired glucose response to an oral glucose load, however, are reported in hyperaldosteronism. 9 Thus, the exact relationship between hypokalemia and worsening of insulin resistance is unclear but appears most pronounced in those with preexisting impaired glucose tolerance and not all people.Given this background, combining an agent that reduces potassium loss, ie, an RAS blocker with a thiazide diuretic, should reduce the risk of new-onset diabetes mellitus. Unfortunately, the Study of Trandolapril/Verapamil SR and Insulin Resistance failed to support this...