Secondary hypertension is high blood pressure caused by an identifiable medical condition or substance, rather than developing on its own over time. It accounts for up to 10% of all hypertension cases in adults. The distinction matters because treating the underlying cause can sometimes bring blood pressure back to normal, something that isn’t possible with the more common form of high blood pressure, which has no single identifiable trigger.
Most people with high blood pressure have what’s called essential (or primary) hypertension, meaning no specific cause can be pinpointed. Secondary hypertension is the opposite: something concrete is driving the numbers up, whether that’s a kidney problem, a hormone imbalance, a structural heart defect, or even a medication you’re taking regularly.
How It Differs From Primary Hypertension
Primary hypertension typically develops gradually over years, influenced by genetics, diet, activity level, and aging. Secondary hypertension can appear more suddenly, sometimes at an unusual age, and it often doesn’t respond well to standard blood pressure medications. These are the patterns that prompt further investigation.
Current European cardiology guidelines recommend screening for secondary causes in anyone diagnosed with hypertension before age 40, with the exception of obese younger adults, who should first be evaluated for sleep apnea. Other red flags include blood pressure that spikes severely despite multiple medications, or readings that were previously well controlled and suddenly worsen without explanation.
Kidney and Blood Vessel Causes
The kidneys play a central role in regulating blood pressure, so kidney-related problems are among the most common causes of secondary hypertension. Chronic kidney disease, polycystic kidney disease, and narrowing of the arteries that supply the kidneys (called renal artery stenosis) can all push blood pressure up.
When blood flow to the kidneys drops, they interpret this as low blood pressure throughout the body and respond by releasing a hormone called renin. Renin kicks off a chain reaction that ultimately produces a powerful blood vessel constrictor and triggers the adrenal glands to retain sodium and water. The result is higher blood volume and tighter blood vessels, both of which raise blood pressure. This mechanism was first demonstrated in the 1930s and remains one of the best-understood pathways in cardiovascular medicine. Over time, the process also causes thickening of blood vessel walls and heart muscle, compounding the damage.
Hormonal and Adrenal Causes
Several hormone-producing glands can drive secondary hypertension when they malfunction. The adrenal glands, which sit on top of the kidneys, are frequent culprits.
In a condition called primary aldosteronism, one or both adrenal glands produce too much aldosterone, a hormone that tells the kidneys to hold on to sodium and water. The excess fluid raises blood pressure. Screening involves a blood test comparing aldosterone levels to renin levels. A ratio at or above a certain threshold, combined with elevated aldosterone, signals a positive screen that warrants further testing. Primary aldosteronism is more common than previously thought and is now considered a leading endocrine cause of secondary hypertension.
A rarer but more dramatic adrenal problem is pheochromocytoma, a tumor that produces surges of adrenaline-like hormones. The classic presentation involves episodes of severe headaches, rapid heartbeat, and heavy sweating, often accompanied by sharp spikes in blood pressure that come and go. Diagnosis relies on measuring breakdown products of these hormones in blood or urine samples.
Thyroid disorders (both overactive and underactive) and Cushing’s syndrome, where the body produces too much cortisol, can also contribute to elevated blood pressure.
Sleep Apnea and Blood Pressure
Obstructive sleep apnea is one of the most frequently overlooked causes of secondary hypertension. During sleep, the upper airway repeatedly collapses and blocks airflow, sometimes hundreds of times per night. Each episode drops oxygen levels and raises carbon dioxide, which jolts the nervous system into a fight-or-flight response.
This repeated activation of the sympathetic nervous system increases levels of stress hormones that constrict blood vessels. It also stimulates the same renin pathway involved in kidney-related hypertension. What makes sleep apnea particularly insidious is that these effects don’t stay confined to nighttime. Elevated stress hormone levels and nervous system overactivity carry over into daytime hours, producing sustained high blood pressure even while you’re awake and breathing normally. If your blood pressure is difficult to control and you snore heavily, feel unrested in the morning, or have been told you stop breathing during sleep, sleep apnea may be a contributing factor.
Medications and Substances
Sometimes secondary hypertension isn’t caused by a disease at all but by something you’re putting in your body. Common pain relievers like ibuprofen and naproxen (nonsteroidal anti-inflammatory drugs, or NSAIDs) are among the most frequent offenders, particularly in people already taking blood pressure medication. These drugs promote sodium retention and can interfere with how well blood pressure medications work. One clinical trial found that certain COX-2 inhibitors caused significant increases in blood pressure in diabetic patients whose hypertension had previously been controlled.
Other substances that can raise blood pressure include alcohol, oral contraceptives, decongestants, certain antidepressants, and stimulants like cocaine and amphetamines. A clue that medication is the culprit: previously stable blood pressure that suddenly becomes difficult to manage, or new hypertension that coincides with starting a new drug or supplement.
Structural Heart Defects
Coarctation of the aorta is a congenital narrowing of the body’s main artery. It’s typically identified in childhood or adolescence but can occasionally go undetected into adulthood. The narrowing forces the heart to pump harder to push blood past the obstruction, raising blood pressure in the upper body while leaving it low in the legs. A telltale sign is a significant difference in blood pressure readings between the arms and legs, along with weak or delayed pulses in the lower extremities. This is one of the reasons blood pressure checks during a physical exam sometimes include measurements at both the arm and ankle.
Diagnosis and What to Expect
Diagnosing secondary hypertension starts with recognizing that something unusual is going on. Your doctor may suspect it based on your age at diagnosis, how severe your blood pressure is, how many medications it takes to control it, or specific symptoms like episodes of flushing, sweating, or muscle weakness. From there, testing is targeted to the suspected cause: blood and urine tests for hormonal conditions, imaging of the kidneys or adrenal glands, sleep studies for apnea, or an echocardiogram for structural problems.
The process can take time because there’s no single test that checks for every possible cause. Often, the most common conditions are ruled out first before moving to rarer possibilities.
Treatment and Outlook
The defining advantage of secondary hypertension over primary hypertension is that it can sometimes be resolved entirely. Treating the root cause, whether that means surgically correcting a narrowed artery, removing an adrenal tumor, managing sleep apnea with a breathing device, or stopping a blood-pressure-raising medication, can bring readings back to normal.
That said, blood pressure doesn’t always normalize completely. Long-standing hypertension can cause lasting changes to blood vessels and the heart, and some underlying conditions can be managed but not fully cured. In those cases, you may still need blood pressure medication to stay in a healthy range. The outlook is generally positive, though, because even partial treatment of the underlying cause often makes blood pressure much easier to control than it was before the diagnosis.