Brain hemorrhages happen when a blood vessel in or around the brain ruptures, allowing blood to leak into surrounding tissue. The most common cause is chronic high blood pressure, but head injuries, blood vessel abnormalities, blood-thinning medications, and drug use can all trigger a bleed. Understanding these causes helps clarify who’s most at risk and why.
High Blood Pressure Is the Leading Cause
Uncontrolled high blood pressure is responsible for more brain hemorrhages than any other single factor. Over time, elevated pressure damages the walls of small arteries deep inside the brain, a process called hypertensive arteriopathy. These tiny penetrating arteries supply structures like the thalamus, basal ganglia, and brainstem. Years of excessive force against their walls weakens the lining, and eventually one of those vessels gives way.
The damage isn’t only from a consistently high reading. Surges and wide fluctuations in blood pressure also play a role in triggering a rupture. This is why someone whose pressure swings dramatically, even if it’s sometimes in a normal range, still faces elevated risk. Research tracking over 1,100 people who had already survived a brain hemorrhage found that inadequate blood pressure control roughly tripled or quadrupled the odds of a second bleed, depending on where in the brain it occurred. For every 10-point rise in systolic pressure (the top number), the risk of recurrence climbed by 33% to 54%. Current guidelines recommend keeping blood pressure at or below 130/80 for people at risk.
Head Injuries and Trauma
A hard blow to the head from a fall, car accident, or sports collision can tear blood vessels and cause bleeding in several distinct locations around the brain. The type of bleed depends on which vessels are damaged.
- Epidural bleeding typically follows a skull fracture at the temple, which tears an artery running along the inside of the skull. Blood collects between the skull and the brain’s outer covering, building pressure quickly.
- Subdural bleeding results from tearing of small veins that bridge the space between the brain and its protective membranes. This is more common in older adults and people on blood thinners, because their bridging veins are more fragile or their blood doesn’t clot as readily.
- Subarachnoid bleeding can occur when trauma damages vessels beneath the thin membrane that closely covers the brain’s surface.
Traumatic brain bleeds can range from slow, low-grade leaks that develop symptoms over days or weeks to rapid, life-threatening emergencies that require surgery within hours.
Aneurysms and Vascular Malformations
Some people have structural weaknesses in their brain’s blood vessels that can rupture without any trauma at all.
Brain Aneurysms
An aneurysm is a balloon-like bulge in a blood vessel wall. Many people live with small, unruptured aneurysms and never know it. Size matters: aneurysms smaller than 3 millimeters carry a low risk of bursting, while those larger than 3 millimeters pose a progressively higher risk. When an aneurysm does rupture, blood spills into the space surrounding the brain, causing a subarachnoid hemorrhage. This is a medical emergency with a high fatality rate.
Arteriovenous Malformations
An AVM is a tangle of blood vessels where arteries connect directly to veins, bypassing the normal network of tiny capillaries that slow blood flow and reduce pressure. Without that buffer, high-pressure arterial blood rushes straight into thin-walled veins that aren’t built to handle it. Over time, this stress can cause the malformation to rupture. The risk of an AVM bleeding in any given year is around 2% to 3%, which sounds small but accumulates significantly over a lifetime, especially since most AVMs are present from birth.
Blood-Thinning Medications
Medications that reduce clotting save lives by preventing heart attacks and strokes caused by blood clots, but they also make it harder for the body to stop bleeding when a vessel is damaged. This trade-off means all blood thinners carry some risk of brain hemorrhage.
A large Danish study covering over 16,000 cases of brain hemorrhage found that nearly 45% of patients were taking some form of blood-thinning or antiplatelet medication at the time of their bleed. Older-generation blood thinners like warfarin carried the strongest association, roughly 2.8 times the odds of a brain bleed compared to non-users. Newer blood thinners (sometimes called DOACs) had a lower but still meaningful association at about 1.8 times the odds. Even common antiplatelet drugs like low-dose aspirin increased the odds by about 50%.
This doesn’t mean you should stop taking a prescribed blood thinner. For most people on these medications, the risk of a clot-related stroke without the drug is higher than the risk of a brain bleed with it. But it does explain why doctors carefully weigh the benefits and risks before prescribing them, especially for older patients.
Stimulant Drugs: Cocaine and Methamphetamine
Cocaine and methamphetamine are potent triggers for brain hemorrhage, particularly in younger adults who might otherwise seem at low risk. These drugs cause a sudden, dramatic spike in blood pressure that can overwhelm blood vessel walls. Methamphetamine also causes blood vessels in the brain to constrict forcefully, and it breaks down the protective barrier between the bloodstream and brain tissue within hours of use.
With repeated use, the damage compounds. Chronic methamphetamine use accelerates the development of high blood pressure, promotes the formation of aneurysms, and weakens vessel walls over time. Someone who uses stimulants regularly may develop the kind of vascular damage that usually takes decades of untreated hypertension to produce, but in a fraction of that time.
Other Contributing Causes
Several less common conditions also lead to brain hemorrhages. A buildup of a specific protein in the walls of brain arteries, a condition more common in older adults, makes those vessels brittle and prone to leaking. Brain tumors can erode into nearby blood vessels or form their own fragile blood supply that bleeds easily. Atherosclerosis, the same fatty plaque buildup that causes heart disease, can also weaken arteries in the brain.
Pregnancy and childbirth carry their own set of risks. Conditions like eclampsia involve dangerous spikes in blood pressure that can trigger a brain bleed, and changes to blood vessel walls after delivery (postpartum vasculopathy) occasionally cause hemorrhage as well. Bleeding disorders, whether inherited or acquired, reduce the body’s ability to clot and raise the risk of any type of hemorrhage, including in the brain. Smoking also contributes by accelerating damage to blood vessel walls throughout the body.
Why Multiple Risk Factors Matter
Brain hemorrhages rarely have a single, isolated cause. More often, several risk factors overlap. Someone with moderately high blood pressure who also takes a blood thinner and smokes faces a compounding risk that’s greater than any one factor alone. The vessel wall weakened by years of elevated pressure is more likely to rupture if the blood can’t clot properly to seal a small leak.
The most modifiable of these risks is blood pressure. Keeping it controlled addresses the single biggest contributor to brain hemorrhage and reduces the danger posed by many of the other risk factors on this list. Avoiding stimulant drugs, managing medications carefully with your prescriber, and addressing smoking all further lower the odds.