High blood pressure (hypertension) affects roughly one in three adults worldwide and is the single largest risk factor for heart disease and stroke. While lifestyle changes — reducing sodium intake, exercising regularly, maintaining a healthy weight — form the foundation of treatment, most patients eventually need medication to reach their target blood pressure.

Modern antihypertensive therapy relies on five well-established drug classes, each acting through a different mechanism. Understanding these mechanisms helps explain why certain drugs are preferred for certain patients.

Angiotensin-converting enzyme (ACE) inhibitors block the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. By reducing angiotensin II levels, blood vessels relax and blood volume decreases. ACE inhibitors are first-line therapy for patients with diabetes, heart failure, or chronic kidney disease. The most common side effect is a persistent dry cough, occurring in 5–20% of patients. A rarer but serious risk is angioedema — sudden swelling of the face, lips, or throat.

ARBs block the AT1 receptor where angiotensin II acts, achieving a similar effect to ACE inhibitors without interfering with bradykinin metabolism. This means ARBs rarely cause cough, making them an excellent alternative for patients who cannot tolerate ACE inhibitors. They share the same renal and cardiac benefits.

Beta-blockers reduce heart rate and cardiac output by blocking beta-1 adrenergic receptors in the heart. They are particularly useful in patients with a history of heart attack, heart failure, or certain arrhythmias. Common side effects include fatigue, cold extremities, and — in some patients — worsening of asthma symptoms. Newer, cardioselective beta-blockers (bisoprolol, nebivolol) have fewer respiratory effects.

These drugs prevent calcium from entering smooth muscle cells in blood vessel walls, causing vasodilation and reducing peripheral resistance. Dihydropyridines like amlodipine primarily affect blood vessels, while non-dihydropyridines (diltiazem, verapamil) also slow heart rate. Ankle swelling and flushing are the most common side effects of dihydropyridines.

Thiazide diuretics reduce blood volume by increasing sodium and water excretion in the kidneys. They are among the oldest and best-studied antihypertensives, and remain a cornerstone of combination therapy. Monitoring potassium levels is important, as thiazides can cause hypokalemia. They may also increase blood glucose and uric acid levels.

Current guidelines recommend starting with two drugs at lower doses rather than one drug at full dose. Common combinations include ACE inhibitor + calcium channel blocker, or ARB + diuretic. Fixed-dose combination pills improve adherence by reducing the number of tablets a patient must take daily.

If you experience persistent headaches, chest pain, visual disturbances, or blood pressure readings above 180/120 mmHg, seek immediate medical attention. Never stop or change your blood pressure medication without consulting your healthcare provider — abrupt discontinuation of beta-blockers, in particular, can cause rebound hypertension.