Can Low-Dose Aspirin Cause Stomach Problems?

Low-dose aspirin, typically taken at 75 to 100 milligrams daily, can and does cause stomach problems in a meaningful number of users. The side effects range from everyday discomfort like heartburn and nausea to serious complications including stomach ulcers and gastrointestinal bleeding. The estimated excess risk of developing a troublesome or complicated ulcer is roughly five extra cases per thousand aspirin users per year, which may sound small until you consider the tens of millions of people taking a daily aspirin worldwide.

How Common Are Stomach Problems on Low-Dose Aspirin?

About one in four people taking daily low-dose aspirin reports some kind of gastrointestinal symptom, according to survey data from a large Dutch population study. That includes heartburn, stomach pain, bloating, and nausea.

More serious outcomes are less frequent but far from rare. A systematic review of observational studies found that gastrointestinal bleeding occurred at a rate of roughly 0.5 to 3.6 cases per thousand person-years among low-dose aspirin users, and the overall risk of GI bleeding was about 40 percent higher than in non-users.¹ For upper GI bleeding specifically, the risk roughly doubled. These figures translate to thousands of additional hospitalizations each year across large populations.

People starting aspirin for the first time face a particularly elevated risk. Two large cohort studies found that new users of low-dose aspirin had roughly 1.7 to 2.8 times the risk of developing stomach ulcers and 1.7 to 3.9 times the risk of duodenal ulcers compared with non-users.² The risk appears highest in the early months of use and then settles somewhat, though it never disappears entirely.

Why Even a Small Dose Damages the Stomach

Aspirin works by blocking an enzyme called cyclooxygenase (COX), which is the same mechanism that makes it useful for preventing blood clots. The problem is that COX also drives the production of prostaglandins in the stomach lining. These prostaglandins are not incidental; they maintain the protective mucus barrier, stimulate bicarbonate secretion that neutralizes acid, and keep blood flowing to the tissue so it can repair itself. When aspirin suppresses COX, the stomach loses its main line of defense against its own acid.

What surprises many people is how sensitive this system is to even tiny amounts of aspirin. In a study testing aspirin doses as low as 10 milligrams, every dose cut gastric prostaglandin levels to about 40 percent of baseline.³ That is a dose far below even a baby aspirin. The prostaglandin suppression is essentially maxed out at the doses most people take for heart protection, meaning there is no meaningful dose threshold below which the stomach stays fully protected.

Animal research has helped clarify what happens at the tissue level once prostaglandins drop. Mucus production falls, the mucus that remains changes in quality, and the surface of the stomach lining becomes less water-repellent, making it easier for acid to penetrate and start eroding tissue.⁴ This is a systemic effect, not just a local one from the pill sitting in your stomach. Even if aspirin is absorbed elsewhere in the body, the stomach still suffers because the prostaglandin suppression happens through the bloodstream.

Beyond the Stomach

Most people think of aspirin-related GI problems as a stomach issue, and that is where the worst of the damage tends to occur. But the injury does not stop there. Ulcers are the most common cause of hospitalization for upper GI bleeding, and aspirin is one of the primary drugs implicated.⁵ The spectrum runs from stomach ulcers to duodenal ulcers to erosions lower in the small intestine.

The small bowel is an underappreciated site of aspirin damage. A study using capsule endoscopy in patients with obscure GI bleeding found that erosive lesions were common among chronic low-dose aspirin users, appearing throughout the jejunum and ileum. When aspirin was combined with another antiplatelet drug like clopidogrel, the proportion of outright ulcers increased.⁶ These small-bowel injuries can be hard to detect because standard upper endoscopy does not reach that far, which means some aspirin-related GI damage goes undiagnosed for a long time.

Animal research has started to reveal the mechanism behind this small intestinal damage. Aspirin appears to disrupt the intestinal barrier, increase gut permeability, and trigger oxidative stress that damages the lining at a cellular level. This is separate from the prostaglandin-related damage in the stomach, which helps explain why some protective strategies that work well for the stomach do not help as much further down the tract.

Who Faces the Highest Risk

Not everyone on low-dose aspirin develops problems. Several factors substantially increase the odds, and understanding them can make a real difference in whether aspirin therapy stays safe or becomes dangerous.

Age: Older adults are more vulnerable. The ASPREE trial, a major randomized study of aspirin in healthy people aged 70 and older, found that major hemorrhage occurred at a rate of about 8.6 events per thousand person-years in the aspirin group versus 6.2 in the placebo group.⁷ That 38 percent increase in major bleeding is why guidelines have shifted against starting aspirin for primary prevention in people over 60.
Helicobacter pylori infection: This common stomach bacterium and aspirin together do more damage than either alone. A meta-analysis found that H. pylori infection raised the risk of aspirin-associated ulcers by almost 70 percent overall, and nearly doubled it among people not already taking acid-suppressing medication.⁸ H. pylori independently weakens the stomach’s mucosal defenses, so when aspirin knocks down prostaglandins on top of that, the lining is attacked from two directions.
Blood thinners and other antiplatelet drugs: Adding aspirin to warfarin, for instance, sharply raises bleeding risk. In one study of patients with coronary stents on both warfarin and aspirin, upper GI bleeding occurred in 20 percent of patients, compared with zero percent of those on warfarin alone.⁹ A larger study confirmed the pattern: combination warfarin-plus-aspirin therapy produced significantly more bleeding events, more emergency department visits, and more hospital admissions related to bleeding than warfarin alone.¹⁰
History of ulcers or GI bleeding: If you have had a stomach ulcer or GI bleed before, aspirin is much more likely to cause a recurrence. This is one of the strongest individual predictors and one that guidelines consistently flag.
Concurrent NSAID use: Taking ibuprofen, naproxen, or other anti-inflammatory drugs alongside aspirin compounds the COX-inhibiting effect and dramatically raises ulcer risk.

Enteric Coating Is Not the Answer

Many people assume that enteric-coated aspirin protects the stomach because the pill dissolves further down in the digestive tract rather than in the stomach itself. The evidence does not support this. A systematic review of the research concluded that enteric-coated aspirin was not an effective strategy for GI protection.¹¹

An epidemiological study comparing plain and enteric-coated aspirin found that the risk of upper GI bleeding and perforation was essentially the same for both formulations. The relative risk was 2.3 for enteric-coated aspirin versus 1.9 for plain aspirin, a difference that was not statistically meaningful.¹² A survey of thousands of aspirin users similarly found no difference in GI symptoms between the two formulations.¹³

The reason enteric coating fails goes back to mechanism. Because aspirin’s stomach damage is primarily systemic rather than from direct contact between the pill and the stomach wall, routing the pill past the stomach does not address the core problem. The aspirin still enters the bloodstream, still suppresses COX systemically, and still depletes prostaglandins in the stomach lining. Worse, some research suggests enteric-coated aspirin shifts damage to the small intestine, where it is harder to detect and treat.

What Actually Protects the Stomach

Proton pump inhibitors (PPIs) are the most effective strategy for preventing aspirin-related stomach damage, and the evidence is convincing. A meta-analysis found that PPIs reduced the odds of developing aspirin-associated upper GI ulcers by roughly 84 percent and cut the odds of GI bleeding by about 73 percent compared with no protection.¹⁴ These drugs work by suppressing acid production, which reduces the damage that acid can do once aspirin has weakened the protective barrier.

PPIs also outperform the older class of acid-suppressing drugs known as H2-receptor antagonists. A separate meta-analysis directly comparing the two found that PPIs were substantially better at preventing both ulcers and bleeding in aspirin users.¹⁵ In clinical trials, adding a PPI like esomeprazole brought the rate of endoscopic ulcers in aspirin users down from over 5 percent to under 2 percent over six months, and also reduced heartburn and erosive esophagitis.¹⁶

For people with a history of ulcer bleeding who need antiplatelet therapy, the combination of aspirin plus a PPI has proven far superior to switching to clopidogrel (a different antiplatelet drug). In a head-to-head trial, recurrent ulcer bleeding occurred in about 8.6 percent of patients switched to clopidogrel versus just 0.7 percent of those kept on aspirin with a PPI added.¹⁷ This finding reshaped clinical thinking: rather than abandoning aspirin, the better strategy is to protect the stomach while continuing it.

Testing and treating for H. pylori infection is another protective measure. Various clinical consensus groups recommend screening aspirin users who have a history of peptic ulcers or GI bleeding for H. pylori and eradicating it if found.¹⁸ Eliminating the infection removes one of the amplifying factors for aspirin-related damage, though it does not eliminate the risk entirely.

The Shifting Landscape of Daily Aspirin

For decades, a daily low-dose aspirin was practically a default recommendation for anyone worried about heart attacks and strokes. That era is ending. In 2022, the U.S. Preventive Services Task Force issued updated guidance recommending against starting aspirin for primary cardiovascular prevention in adults 60 and older, citing the increasing risk of bleeding complications that comes with age. For adults 40 to 59 with elevated cardiovascular risk, the decision is now framed as an individual one to be made with a doctor, not a blanket recommendation.¹⁹

The shift was driven by several large trials showing that for people who have never had a heart attack or stroke, the reduction in cardiovascular events from daily aspirin was largely offset by the increase in bleeding events.²⁰ The balance tips more favorably for people who already have heart disease (secondary prevention), where the cardiovascular benefit is larger and clearer. But for healthy people taking aspirin “just in case,” the stomach and bleeding risks now weigh more heavily in the calculus than they used to.

The practical upshot: if your doctor prescribed aspirin after a heart attack or for a known cardiovascular condition, the benefit almost certainly outweighs the GI risk, especially if you are also taking a PPI. But if you started taking a daily aspirin on your own as a general health measure, the current evidence suggests that conversation with a doctor is worth having. The GI side effects are real, cumulative over years of use, and potentially serious.²¹

Symptoms Worth Watching For

Not all aspirin-related stomach damage announces itself with obvious symptoms. Some ulcers bleed slowly and silently, showing up only as unexplained anemia or dark, tarry stools. Overt signs include persistent stomach pain, burning in the upper abdomen, nausea, and vomiting. Any blood in the stool or vomit, whether bright red or dark and coffee-ground-like, warrants immediate medical attention.

The GI side effects of aspirin remain a clinical concern in both symptomatic and asymptomatic patients, which means that feeling fine does not guarantee your stomach lining is fine.⁵ People who have been on aspirin for years without problems can still develop ulcers or bleeding, because the prostaglandin suppression is ongoing and cumulative wear on the mucosal barrier can eventually cross a threshold. If you are on long-term aspirin and develop new digestive symptoms, even ones that seem minor, mentioning them to your doctor lets them decide whether investigation or a protective co-prescription is warranted.