Thiazide diuretics and related compounds are used in mild or moderate heart failure and hypertension (high blood pressure). They have a potent action, and work by inhibiting sodium reabsorption in the kidneys having an anti-hypertensive effect and reducing oedema (excess body water).
Diuretics have a diuresis effect (increased urine output) which can act within 1-2 hours (last for over 12 hours), therefore these medicines are best taken in the morning to prevent interference with sleep.
They have been extensively studied and shown to reduce the risk of both stroke and heart attack in people with high blood pressure.
They are usually started in low dosages which are often very effective.