Diuretics are the most commonly prescribed anti hypertensive agents.Thiazide diuretics which was introduced many decades ago , lost popularity in recent years , again got a second life after the publication of ALLHAT trial recently. Now diuretics has become the the drug of first choice in almost any hypertension unless any specific contraindication.
The most commonly used thaizide is hydrochlorthiazide ,and chlorthalidone.The blood pressure reducing effect is so consistent and smooth , all the currently popular molecules like ACE inhibitors and ARBs come with a combination with thiazide. While every one is clear diuretics are effective anti hypertensive agent How it does is not clear.
How does a diuretic reduce blood pressure?
A. The exact mechanism is not clear. May not be uniformly effective in all patients with HT.
B . Salt sensitive HT respond well to diuretics.
C. Volume correction /free water clearance might be a factor
D. Direct effect on vascular smoth muscle documented.The sodium transporter is blocked and hence calcium : sodium exchange is prevented .This depletes intracellular calcium in vascular smooth muscle cells .Less calcium for actin myosin interaction and hence vasodilatation
E. Thiazides combine well with all other antihypertensive drugs (ACEI, ARB, Beata blockers, calcium blockers)
F. Loop diuretics like frusemide can never be a good antihypertensive agent.
Dr.S.Venkatesan MD 
