Hypertension, usually called high blood pressure, is a long-term condition in which the pressure of blood pushing against the walls of the arteries stays too high, which over years raises the risk of stroke, heart attack, heart failure, kidney disease and dementia [1,2].
This page provides general information. It does not replace advice from a doctor or another qualified healthcare professional.
Arteries carry blood from the heart around the body. The push of blood against their walls is blood pressure [8].
What the two numbers mean. A reading is written as two numbers, such as 130/80. The first and higher number, systolic pressure, is the pressure while the heart squeezes and pushes blood out. The second, diastolic pressure, is the pressure while the heart relaxes between beats [1,8]. The unit mm Hg means millimeters of mercury. Blood pressure varies through the day, so high blood pressure means it stays high even at rest [8].
The United States and Europe use different numbers, and this genuinely confuses people. United States guidance defines high blood pressure as consistently 130/80 mm Hg or higher [2,5]. European and United Kingdom guidance keeps 140/90 mm Hg or higher, treating readings in between as raised rather than as a diagnosis [1,3,7]. The gap is real: the lower cut-off labels about 46% of United States adults as hypertensive, against about 32% under the higher one [7]. Identical readings can therefore mean a diagnosis in one country and not in another [5,7].
Not the same as pulmonary hypertension. The two are constantly confused. Pulmonary hypertension is raised pressure in the arteries between the heart and lungs, a different and much rarer condition, covered in our separate guide.
An estimated 1.4 billion adults aged 30 to 79 had high blood pressure in 2024, roughly a third of that age group, up from 650 million in 1990 as populations have grown older. Two-thirds of them live in low- and middle-income countries [1].
Those figures count measured blood pressure, not diagnoses. About 600 million, some 44%, are unaware of it, and only about 320 million, some 23%, have it under control [1]. Around 5 million adults in the United Kingdom are thought to have it undiagnosed [8]. National figures are hard to compare, since surveys differ in ages and thresholds.
For most people no single cause is found. This is called primary or essential hypertension, and it builds up slowly over years [8]. Several things raise the chances of it, none of them a moral failing.
Things that raise the risk. Getting older is the strongest single factor, and having close relatives with high blood pressure raises risk too [1,3]. People of Black African, Black Caribbean or South Asian background are at higher risk in the United Kingdom [3]. Eating a lot of salt, drinking a lot of alcohol, carrying extra weight, being inactive and smoking all contribute [1,2,3,8].
Secondary hypertension, where a cause is found. In a smaller group, another condition or medicine is driving the pressure up. Known causes include kidney disease, diabetes, obstructive sleep apnea, which is repeated interruption of breathing during sleep, and some medicines including oral contraceptives and certain herbal remedies [8]. A cause is worth looking for when the pressure is very high, appears suddenly or young, or resists several medicines [8,9].
The single most important thing to know is that high blood pressure usually causes no symptoms at all. Many people have it for years without knowing, and measuring it is the only way to find out [1,2].
Headaches and nosebleeds are not reliable warning signs. That belief is one reason the condition goes undetected. High blood pressure only rarely causes symptoms, and when headaches, blurred vision or nosebleeds do occur they usually have another explanation [3,8].
Very high blood pressure, usually 180/120 mm Hg or higher, can cause severe headache, chest pain, dizziness, breathlessness, nausea, vision changes and confusion [1].
When to seek urgent help. A reading of 180/120 mm Hg or higher with any of those symptoms needs emergency care [1]. Call emergency services, 999 in the United Kingdom or 911 in the United States, for chest pain that does not go away or spreads to an arm, the neck, jaw or back, since this may be a heart attack [3]. Sudden weakness, a drooping face, slurred speech or loss of vision needs the same call, since these can be signs of a stroke [1,2]. A very high reading with no symptoms means contacting your team promptly, not an emergency department [5].
A family doctor, practice nurse or pharmacist checks it using a cuff around the upper arm [3].
One reading does not make a diagnosis. Clinic readings are often higher because people feel anxious. Hypertension is confirmed on readings taken on separate occasions, and it is usual to be asked to monitor at home for several days or to wear a portable monitor that records over 24 hours, called ambulatory monitoring [1,3,8].
White coat and masked hypertension. White coat hypertension means readings are high in the clinic and normal away from it. Masked hypertension is the reverse. Out-of-office monitoring is what separates the two, which is why home and ambulatory measurement have moved to the center of diagnosis rather than the edge of it [4,7]. Masked hypertension carries risk a clinic reading would miss, while white coat hypertension can lead to treatment that is not needed [7].
Guidance advises against relying on cuffless devices, including smartwatches, until they are shown to be more precise [5]. Blood and urine tests and a heart tracing may also be arranged [8].
Treatment lowers the risk of stroke, heart attack, heart failure and kidney damage: each 10 mm Hg fall in systolic pressure is linked to roughly a quarter lower stroke risk [1,2,6].
Everyday changes. Guidance recommends more vegetables and fruit, less salt, more dietary potassium, more movement, stopping tobacco, reducing or stopping alcohol, and reaching or keeping a weight that is healthy for the individual [1,5]. Many who make these changes still need medicine, and needing medicine is not a personal failure [1].
The main medicines, described by what they do [1,6]:
Most people need more than one medicine, and that is expected. United States guidance prefers starting with two of different classes combined in a single pill, since one tablet is easier to keep taking than two [5]. Staying on treatment is the biggest practical problem in hypertension care: medicines work only while they are taken, and fewer than half of people prescribed spironolactone are still taking it a year later [10]. Anyone struggling is better off saying so than stopping quietly.
Resistant hypertension. When pressure stays above target despite three medicines of different classes at proper doses, including a diuretic, it is called resistant hypertension. Confirming it means checking the medicines are being taken and excluding the white coat effect [9]. Spironolactone, which blocks the hormone aldosterone, is the usual fourth medicine to add [10]. Renal denervation, threading a thin tube to the kidney arteries to quiet the nerves in their walls, is an option where medicines are not enough. Radiofrequency and ultrasound systems were approved in the United States in November 2023, and European societies accept it for true resistant hypertension [10].
Most care happens in general practice, with annual review once it is controlled and more frequent checks when a medicine or dose changes [8]. Keeping a record of home readings helps a clinician see patterns [8].
Blood pressure in pregnancy. Around 1 in 10 women in the United Kingdom develop high blood pressure during pregnancy [8], and hypertensive disorders affect 5% to 10% of pregnancies in the United States [12]. Pre-eclampsia is raised blood pressure of 140/90 mm Hg or higher together with protein in the urine after 20 weeks, and it affects 3% to 8% of women who give birth worldwide [11]. Symptoms can include a persistent headache, changes in vision, upper stomach pain, nausea and swelling of the face or hands, though some women have none [11,12]. Untreated it can progress to eclampsia, which involves seizures and is a medical emergency [11]. Antenatal blood pressure and urine checks are how it is caught early, magnesium sulfate more than halves the risk of eclampsia, and low-dose aspirin lowers the risk for women at higher risk [11]. Anyone planning a pregnancy should ask which of their medicines are safe to continue [12].
Clinical trials test whether a treatment works and is safe. Blood pressure research is active, particularly for people whose readings stay high despite several medicines. Deciding whether to look into a study is personal, and it helps to take it in steps.
Worth being clear on what a study involves:
Every trial has rules about who can take part, called eligibility criteria. For a high blood pressure study they might include a confirmed diagnosis, an average systolic reading inside a set range such as 140 to 170 mm Hg, a set number of medicines already taken at their highest tolerated doses, kidney function and blood potassium inside set limits, and not being pregnant or planning a pregnancy.
trialport’s medifit helps people consider information related to possible medical suitability. It does not diagnose a condition, confirm eligibility or replace formal screening by the study team.
Explore high blood pressure clinical trials through trialport
A study can look right on paper and still be hard in practice:
trialport’s readifit helps people reflect on their understanding, motivation, time, routines, support, emotions and practical arrangements.
Useful questions to put to a research team:
Taking part is voluntary. A person can ask questions, speak with people they trust and choose not to participate.
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Study status checked: 3 August 2026. Research moves quickly, so this list will date. For current information, search at app.trialport.com.
Coverage varies. Many countries have a general heart charity rather than a blood pressure organization, and the treating clinic is then the best route.
Joe Montana, the American football quarterback who won four Super Bowls with the San Francisco 49ers, described his own high blood pressure in 2006. He found out at a routine appointment after turning 40, feeling perfectly well. “That’s the scary part,” he said. “High blood pressure usually doesn’t have symptoms, so I wouldn’t have known if I hadn’t gone in that day.” He also described his surprise when his first medicine did not work, and learning that most people need more than one [17].
Can I tell when my blood pressure is high?
No. It usually causes no symptoms, and feeling stressed or relaxed says nothing about the numbers [1,2].
Is high blood pressure 130/80 or 140/90?
Both, depending on where you are. United States guidance uses 130/80 mm Hg or higher; European and United Kingdom guidance uses 140/90 and treats readings in between as raised [2,3,7].
Why does my reading differ at home and at the doctor?
Clinic readings are often higher, which is why United Kingdom home thresholds are lower, at 135/85 mm Hg [3,8].
Will I have to take tablets for the rest of my life?
Usually yes, though the mix can change. There is no cure, and medicines work only while they are taken. Anyone wanting to reduce or stop should discuss it first [1,10].
Do headaches or nosebleeds mean my blood pressure is high?
They are not reliable signs. Severe headache alongside a reading of 180/120 mm Hg or higher does need urgent attention [1,3].
Is high blood pressure the same as pulmonary hypertension?
No. Pulmonary hypertension affects the arteries between the heart and the lungs, and it is a different, much rarer condition. See our pulmonary hypertension guide.
Can a smartwatch measure my blood pressure?
Not reliably yet. Guidance advises against relying on cuffless devices until they are shown to be more precise [5].
Written by: trialport editorial team
Reviewed by: Keith Berelowitz, Founder and CEO, trialport
Reviewed on: 3 August 2026
Next review due: 3 August 2027
References last checked: 3 August 2026