Can Aspirin Lower Blood Pressure? What the Science Says

The best available evidence says aspirin does not meaningfully lower blood pressure on its own. A 2024 meta-analysis pooling data from more than 20,000 people with hypertension found no significant drop in either systolic or diastolic blood pressure among those taking aspirin compared to controls. That finding runs counter to a persistent idea, fueled by smaller studies and plausible biology, that aspirin could double as a blood-pressure drug. The reality is more layered than a flat “no,” though, because timing, dose, individual physiology, and the specific clinical context all shift what aspirin appears to do.

What the Largest Pooled Studies Show

The most direct test of aspirin’s blood-pressure effect comes from a systematic review and meta-analysis published in BMC Cardiovascular Disorders in 2024. Researchers combined five studies covering more than 20,000 people with hypertension and found that aspirin did not significantly reduce systolic blood pressure (the pooled difference was less than 1 mmHg) or diastolic blood pressure. Only one of the five individual studies reported a statistically significant drop; the rest showed no difference between aspirin and placebo or no-treatment controls.¹ For context, blood-pressure medications typically lower systolic pressure by at least 5 to 15 mmHg, so even if aspirin nudged pressure down by a fraction of a point, the clinical relevance would be negligible.

Among NSAIDs as a class, aspirin actually looks comparatively benign when it comes to blood pressure. A separate meta-analysis in the Annals of Internal Medicine found that while some NSAIDs can raise blood pressure substantially, aspirin and sulindac had the least hypertensive effect of the drugs studied.² So aspirin does not lower pressure in any clinically important way, but at least it does not tend to raise it the way ibuprofen or piroxicam can.

Why People Thought It Might Work

Aspirin blocks an enzyme called cyclooxygenase, which is involved in making hormone-like chemicals called prostaglandins. Some prostaglandins constrict blood vessels and promote clotting, while others relax vessel walls and discourage clots. The balance between these opposing signals is what gave researchers reason to think aspirin might influence blood pressure. At low doses, aspirin mainly shuts down the clot-promoting side in platelets. At higher doses, it also blocks the vessel-relaxing side in the blood vessel lining, which can actually work against any pressure-lowering benefit.³ This dose-dependent tug of war helps explain why aspirin has never produced a clean, consistent drop in pressure across studies.

Higher aspirin doses have also been linked to reduced kidney blood flow, which would actually push pressure upward. A review in Revista Portuguesa de Cardiologia noted that larger aspirin doses can impair the kidney’s ability to excrete sodium and water, potentially raising blood pressure rather than lowering it.⁴ So the relationship between dose and effect is not linear; more aspirin does not mean more blood-pressure lowering. If anything, it can tip the scales in the wrong direction.

Aspirin and Nitric Oxide

Separate from its prostaglandin effects, aspirin appears to boost nitric oxide production in blood vessel walls. Nitric oxide is one of the body’s main signals to relax blood vessels, so this pathway caught researchers’ attention as a potential blood-pressure mechanism. Lab studies showed that aspirin at low concentrations increased nitric oxide output from endothelial cells by around 40 to 80 percent in cell-culture experiments.⁵ Further work showed this effect was independent of the cyclooxygenase pathway: aspirin directly modifies the enzyme that produces nitric oxide, making it more active.⁶

In inflammatory conditions, aspirin also seems to protect nitric oxide production from being shut down by inflammatory signals. When inflammatory molecules attack endothelial cells, they suppress nitric oxide output; aspirin can partially reverse that suppression.⁷ These findings are biologically interesting, but they come from cell and animal work, and the nitric oxide boost clearly does not translate into a measurable blood-pressure reduction in the large human trials described earlier. Biology that works in a petri dish does not always move the needle in a living person with all the body’s competing regulatory systems in play.

The Bedtime Dosing Debate

One of the more provocative claims about aspirin and blood pressure involves timing. A small body of research has suggested that taking aspirin at bedtime lowers blood pressure more than taking it in the morning. A 2024 systematic review and meta-analysis pooling several trials reported that bedtime aspirin lowered systolic pressure by roughly 3.6 mmHg and diastolic pressure by about 1.9 mmHg compared to morning dosing.⁸ That sounds meaningful, since even a few points of sustained blood-pressure reduction is associated with lower cardiovascular risk over time.

But the evidence is far from settled. A randomized cross-over trial published in Hypertension found no blood-pressure difference at all between bedtime and morning aspirin in patients with cardiovascular disease, with systolic and diastolic differences of essentially zero.⁹ This study did find that bedtime aspirin reduced platelet reactivity during morning hours more effectively, which matters for clot prevention even if it does nothing for pressure. The discrepancy between studies may come down to the populations tested, the monitoring methods used, and how blood pressure was measured across the 24-hour cycle.

Non-Dippers and Nighttime Blood Pressure

Most people’s blood pressure dips by about 10 to 20 percent during sleep. Those whose pressure stays elevated throughout the night are sometimes called “non-dippers,” and they face higher cardiovascular risk than people whose pressure follows the normal nocturnal decline. Bedtime aspirin appears to have its strongest blood-pressure effect in this particular group. A prospective trial found that non-dippers who took aspirin at bedtime experienced a nocturnal blood-pressure drop roughly double that of dippers taking the same dose, with reductions around 11/7 mmHg in non-dippers versus 5.5/3.3 mmHg in dippers.¹⁰

That is a genuinely substantial drop for a drug not typically classified as blood-pressure medication. Researchers have explored whether bedtime aspirin might even convert non-dippers into dippers, restoring the healthy nighttime pattern.¹¹ The idea is appealing, but the evidence base remains thin. Most of the positive findings come from a small number of research groups, and larger independent replications have not consistently confirmed them. Until bigger, more diverse trials weigh in, treating aspirin as a nighttime blood-pressure tool for non-dippers remains more hypothesis than guideline.

Dose Matters More Than You Might Think

Animal research has underscored a striking dose-dependent split in how aspirin affects the cardiovascular system. In a study using hypertension-prone rats, a high dose of aspirin improved blood vessel function and reduced heart enlargement, but simultaneously triggered immune activation in the kidneys, promoted kidney scarring, and actually raised blood pressure. A lower dose preserved the heart-protective benefits without triggering the harmful immune and blood-pressure effects.¹² This is animal data and does not translate directly to human dosing, but it illustrates a principle that runs through the human evidence too: aspirin’s cardiovascular effects are not simply “more drug, more benefit.” The dose window matters, and getting it wrong can flip the effect.

Aspirin and Blood-Pressure Medications

If you take an ACE inhibitor or a similar blood-pressure drug, you may have heard that aspirin can interfere with it. The concern rests on a real mechanism: ACE inhibitors work partly by increasing a molecule called bradykinin, which in turn promotes vasodilating prostaglandins. Because aspirin blocks prostaglandin production, it could theoretically undermine the ACE inhibitor’s effect.¹³

In practice, the interaction appears to be dose-dependent and clinically modest. A study in patients with heart failure found that aspirin doses of 300 mg or more dulled the hemodynamic effects of the ACE inhibitor enalapril in the short term, but low-dose aspirin (around 236 mg or less) had no effect on blood pressure.¹⁴ Another trial in people with essential hypertension tested aspirin at 81 to 325 mg per day alongside either enalapril or losartan (an angiotensin receptor blocker) and found no significant change in blood pressure from adding aspirin.¹⁵ So at the low doses most people take for heart protection, aspirin is unlikely to meaningfully blunt your blood-pressure medication.

Aspirin and Arterial Stiffness

Blood pressure is not the only measure of vascular health. Arterial stiffness, which reflects how rigid or flexible your blood vessels are, independently predicts cardiovascular events. One randomized trial in people with hypertension found that two weeks of aspirin significantly reduced aortic stiffness, as measured by pulse wave velocity, compared to placebo.¹⁶ A pilot study in exercising adults found similar improvements in arterial stiffness with aspirin use during high-intensity training.¹⁷

These findings suggest aspirin may benefit vascular health through a pathway separate from straight blood-pressure reduction. However, the picture is not uniform. A study comparing aspirin’s vascular effects in people with type 2 diabetes versus matched controls without diabetes found no difference in pulse wave velocity between groups.¹⁸ As with blood pressure itself, aspirin’s vascular effects seem to depend heavily on who is taking it and what underlying condition they have.

Preeclampsia Prevention

The one clinical setting where aspirin’s blood-pressure-related benefits are most widely accepted is pregnancy. Preeclampsia, a dangerous condition involving new-onset high blood pressure and organ damage, affects a significant percentage of pregnancies and can be life-threatening. Low-dose aspirin started in the second trimester has been shown to reduce the risk of preeclampsia, and the U.S. Preventive Services Task Force recommends it for women at high risk. A systematic evidence review found that aspirin reduced preeclampsia risk by about 24 percent, with absolute risk reductions of 2 to 5 percent depending on baseline risk.¹⁹

Even here, though, the evidence is uneven across populations. A large trial reported in the New England Journal of Medicine found no significant difference in preeclampsia incidence between aspirin and placebo groups among high-risk women across several categories, including those with chronic hypertension and previous preeclampsia.²⁰ A more recent systematic review noted that aspirin’s effectiveness varied by ethnicity and was influenced by factors like aspirin resistance and the biomarkers used to identify risk, with significant benefit in some subgroups but not others.²¹ The mechanism likely involves aspirin’s effects on placental blood flow rather than a general blood-pressure reduction, which is why this benefit does not extend to blood-pressure management in non-pregnant people.

Aspirin Resistance in Hypertensive Patients

Not everyone responds to aspirin the same way, and this variability is not limited to blood pressure. A study of hypertensive patients found that roughly one in five showed laboratory evidence of “aspirin resistance,” meaning their platelets were not adequately suppressed despite taking the drug. The frequency was somewhat higher among those with poorly controlled blood pressure (about 26 percent) compared to those whose pressure was well controlled (about 18 percent), though this difference was not statistically significant. Women and people with higher creatinine levels (a marker of kidney function) were at greater risk of being aspirin-resistant.²² If aspirin’s antiplatelet effect is blunted in a given individual, its secondary vascular effects are probably blunted too, which adds one more variable to the already inconsistent picture of aspirin and blood pressure.

Cardiovascular Benefits Without Pressure Reduction

The landmark Hypertension Optimal Treatment (HOT) trial, which enrolled nearly 19,000 people with hypertension, showed that low-dose aspirin reduced major cardiovascular events by 15 percent and heart attacks by 36 percent compared to placebo. Yet aspirin had no effect on stroke, and the benefit was attributed to its antiplatelet action rather than any blood-pressure change.²³ This distinction matters. Aspirin can protect hypertensive patients from heart attacks without touching their blood pressure, which means its cardiovascular value in this population is real even though it works through an entirely different mechanism than pressure reduction.

The same trial flagged a trade-off: non-fatal major bleeds were significantly more common in the aspirin group, roughly doubling compared to placebo, even though fatal bleeds were similar between groups.²³ That bleeding risk is why current guidelines have pulled back from recommending aspirin for primary prevention in many low-to-moderate-risk adults. If you already have well-controlled blood pressure and no history of cardiovascular events, the bleeding hazard may outweigh the clot-prevention benefit. That calculation changes if you have established heart disease, but it is a conversation for your doctor rather than a decision to make based on aspirin’s theoretical effect on a blood-pressure reading.

How Aspirin Went From Fever Remedy to Cardiovascular Staple

Aspirin’s journey is one of the more unusual stories in pharmacology. For most of its early life, it was used for pain and fever. Its antiplatelet properties were not recognized until the mid-twentieth century, and the idea that it could influence blood pressure came even later, riding the wave of prostaglandin research in the 1970s and 1980s.²⁴ Each new mechanism that researchers discovered, from thromboxane inhibition to nitric oxide enhancement, generated fresh hypotheses about what else aspirin might do. The blood-pressure hypothesis was one of those hopeful offshoots. It had enough biological plausibility to sustain decades of investigation, but the clinical evidence never cohered into a strong enough signal to change practice. Aspirin remains a cornerstone of cardiovascular prevention, but for its antiplatelet effects and not because it moves the blood-pressure needle in any reliable way.