Hypertension, also referred to as high blood pressure, HTN or HPN, is a medical condition in which the blood pressure is chronically elevated. In current usage, the word "hypertension" without a qualifier normally refers to arterial hypertension.

Hypertension can be classified either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient's condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e., secondary to) another condition, such as kidney disease or tumours (pheochromocytoma and paraganglioma). Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurysm, and is a leading cause of chronic renal failure. Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, defined as mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.

In individuals older than 50 years, hypertension is considered to be present when a person's systolic blood pressure is consistently 140 mm Hg or greater. Beginning at a systolic pressure of 115 and diastolic pressure of 75 (commonly written as 115/75 mm Hg), cardiovascular disease (CVD) risk doubles for each increment of 20/10 mmHg. Prehypertension is defined as blood pressure from 120/80 mm Hg to 139/89 mm Hg. Prehypertension is not a disease category; rather, it is a designation chosen to identify individuals at high risk of developing hypertension. The Mayo Clinic specifies blood pressure is "normal if it's below 120/80". Patients with blood pressures over 130/80 mm Hg along with Type 1 or Type 2 diabetes, or kidney disease require further treatment.

Resistant hypertension is defined as the failure to reduce BP to the appropriate level after taking a three-drug regimen. The American Heart Association released guidelines for treating resistant hypertension.

Signs and symptoms

Hypertension is usually found incidentally by healthcare professionals measuring blood pressure during a routine checkup. In isolation, it usually produces no symptoms although some people report headaches, fatigue, dizziness, blurred vision, facial flushing, transient insomnia or difficulty sleeping due to feeling hot or flushed, and tinnitus during beginning onset or before hypertension diagnosis.

Hypertension is often confused with mental tension, stress and anxiety. While chronic anxiety and/or irritability is associated with poor outcomes in people with hypertension, it alone does not cause it. Accelerated hypertension is associated with somnolence, confusion, visual disturbances, and nausea and vomiting (hypertensive encephalopathy).