What Causes Bleeding Ulcers? Infections, Drugs & More

Bleeding ulcers are caused, in most cases, by one of two things: infection with the bacterium Helicobacter pylori or regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin. Together these account for the vast majority of peptic ulcers that go on to bleed. But the full picture is broader than those two headline causes, involving drug combinations that multiply risk, lifestyle habits, rare acid-overproduction syndromes, and even the emerging science of non-H. pylori stomach bacteria.

How an Ulcer Starts to Bleed

A peptic ulcer is an open sore in the lining of the stomach or the first part of the small intestine (the duodenum). Most ulcers cause pain, nausea, or no symptoms at all. Bleeding happens when the ulcer burrows deep enough to erode into a blood vessel. The bigger the artery that gets breached, the more severe the bleed. Erosion into a medium or large artery is what causes the dramatic, life-threatening hemorrhages that send people to the emergency room.¹

The damaged artery at the base of a bleeding ulcer is rarely normal tissue that simply got nicked. Surgical specimens show that the artery wall itself is often diseased: inflammation of the artery (arteritis) was found in about 83% of eroded arteries in one study, and roughly half of bleeding points showed abnormal ballooning (aneurysmal dilatation) of the vessel wall.² These structural changes help explain why some ulcers bleed repeatedly even after treatment: a weakened, inflamed artery is more likely to reopen.

Duodenal ulcers deserve special mention. The duodenum sits close to the gastroduodenal artery, a relatively large vessel. When a duodenal ulcer erodes into that artery, the resulting hemorrhage tends to be more dangerous, carrying higher rates of complications and death compared with most gastric ulcers.³

Helicobacter pylori Infection

For decades, stomach ulcers were blamed on stress and spicy food. That changed in 1982 when two Australian researchers discovered H. pylori living in the stomach lining, a finding eventually recognized with the Nobel Prize.⁴ We now know that this corkscrew-shaped bacterium colonizes the stomachs of roughly half the world’s population, though only a fraction develop ulcers.

The bacterium damages the stomach’s protective mucus layer and triggers chronic inflammation. Certain strains are more dangerous than others: bacterial proteins that help the organism stick to stomach cells, along with factors that ramp up inflammation, increase the likelihood of ulcer disease.⁵ Host genetics matter too. Whether your immune system mounts a mild or aggressive inflammatory response to the infection influences your personal risk.

The good news is that eliminating H. pylori with a course of antibiotics dramatically cuts the chance that a bleeding ulcer will come back. One meta-analysis found that rebleeding rates dropped from roughly 24% to under 5% with eradication therapy, and among patients in whom the bacterium was successfully cleared, rebleeding dropped to just 1%.⁶ That is why testing for and treating H. pylori is standard care after any bleeding ulcer.

NSAIDs and Why They Wreck the Stomach Lining

Ibuprofen, naproxen, diclofenac, and other NSAIDs are the second most common cause of peptic ulcers. These drugs relieve pain and inflammation by blocking enzymes called cyclooxygenases. The problem is that the same enzymes also produce prostaglandins, signaling molecules that protect the stomach lining by maintaining its mucus coat, promoting blood flow to the tissue, and regulating acid secretion. When prostaglandin levels drop, the stomach loses its armor against its own acid.⁷

The damage is not just chemical. Animal research shows that prostaglandin deficiency also triggers abnormal stomach contractions, which increase the lining’s permeability, allow immune cells to infiltrate, and generate tissue-damaging free radicals. This chain of events can produce visible stomach lesions even before acid has time to do its usual corrosive work.⁸ That combination of weakened defenses and increased mechanical stress explains why even short courses of NSAIDs can occasionally cause problems, and why long-term daily use raises ulcer risk substantially.

Aspirin and Other Antiplatelet Drugs

Aspirin deserves its own mention because millions of people take low-dose aspirin daily for heart protection. Aspirin is technically an NSAID, so it shares the prostaglandin-suppressing effect described above. But it adds a second problem: it irreversibly blocks platelets, the blood cells responsible for forming clots. That means if an ulcer does start bleeding, the body’s ability to plug the leak is impaired. Gastrointestinal bleeding is a well-documented side effect of long-term antiplatelet therapy, and the choice of antiplatelet drug matters when balancing heart protection against bleeding risk.⁹

For people who have already had a bleeding ulcer and still need aspirin, the picture gets complicated. A trial published in the New England Journal of Medicine compared two strategies: eradicating H. pylori alone versus taking a proton pump inhibitor (PPI) daily. Among aspirin users, both approaches kept rebleeding rates very low, under 2%. But among people taking other NSAIDs like naproxen, relying on H. pylori eradication alone was not enough: nearly 19% rebled within six months, compared with about 4% on daily PPI therapy.¹⁰ The takeaway is that if you need ongoing NSAID therapy, H. pylori treatment alone may not be sufficient protection.

Dangerous Drug Combinations

Some medications that seem harmless on their own sharply increase bleeding risk when combined. The best-documented example involves SSRIs, the widely prescribed class of antidepressants that includes fluoxetine, sertraline, and citalopram. SSRIs reduce serotonin uptake in platelets, which impairs the platelets’ ability to form clots. Take an SSRI alongside an NSAID, and you are compromising the stomach’s protective lining while simultaneously handicapping the clotting response.

A systematic review of eleven studies found that people taking both an SSRI and an NSAID had roughly double the odds of a gastrointestinal bleed compared with those taking an SSRI alone.¹¹ A population-based cohort study put the risk increase in starker terms: combining an SSRI with an NSAID raised the risk of upper GI bleeding by more than twelve-fold, and combining an SSRI with low-dose aspirin raised it about five-fold.¹² If you are on an antidepressant and reach for ibuprofen regularly, this is worth discussing with your doctor.

Other Medications That Can Cause Ulcers

NSAIDs get most of the attention, but several other drug classes can irritate or ulcerate the upper gastrointestinal tract.

• Bisphosphonates: Drugs like alendronate, used to treat osteoporosis, can directly irritate the esophageal and stomach lining. Part of the mechanism appears to involve reduced nitric oxide production, which normally helps protect the mucosa. Taking these pills with a full glass of water and staying upright afterward is not just a suggestion on the label; it is a real injury-prevention measure.¹³
• Potassium supplements: Oral potassium chloride tablets can cause localized ulceration, especially in the esophagus, by creating a concentrated pocket of the mineral against the tissue. The injury is not from acidity; it is a direct chemical burn from the high local concentration of potassium.¹⁴
• Corticosteroids: Prednisone and related drugs, when used alongside NSAIDs, significantly raise ulcer risk. On their own, the evidence is less clear, but combined therapy is a well-recognized danger.

Alcohol and Smoking

Neither alcohol nor smoking will create an ulcer from scratch the way H. pylori or NSAIDs can, but both substantially raise the risk of an existing ulcer bleeding. A population-based cohort study found that heavy drinking, defined as more than 42 drinks per week, quadrupled the risk of a bleeding ulcer compared with near-abstinence.¹⁵ The same study identified smoking as an independent risk factor for both bleeding and perforated ulcers.

Alcohol injures the stomach lining through several routes: it strips away the surface cells, triggers free-radical damage, reduces protective prostaglandin production, and constricts tiny blood vessels in the mucosa, all of which weaken the tissue’s ability to heal.¹⁶ Smoking, for its part, slows ulcer healing, increases acid secretion, and reduces blood flow to the stomach wall. If you already have an ulcer or take NSAIDs, alcohol and cigarettes are making a bad situation worse.

Stress Ulcers in Critically Ill Patients

The idea that everyday psychological stress causes ulcers is largely a myth. But physiological stress, the kind your body undergoes during a severe burn, major surgery, head trauma, or sepsis, is a real and well-documented cause of stomach ulcers. These “stress ulcers” are common enough in intensive care units that preventive treatment is routine.¹⁷

The mechanism involves reduced blood flow to the stomach lining during critical illness, combined with breakdown of the normal mucus barrier. Patients on mechanical ventilation or those with clotting disorders are at particularly high risk. Suppressing acid production with medication is the standard preventive strategy in ICU settings, because keeping acid levels low gives the stressed mucosa a better chance of surviving intact.¹⁸

Zollinger-Ellison Syndrome and Acid Overproduction

In rare cases, bleeding ulcers result from wildly excessive acid production rather than infection or drugs. Zollinger-Ellison syndrome is caused by gastrin-secreting tumors called gastrinomas, usually found in the pancreas or duodenum. The excess gastrin drives the stomach to pump out acid at many times the normal rate, overwhelming the lining’s defenses and producing severe, often multiple ulcers that are resistant to standard treatment.¹⁹ If someone has recurrent ulcers that do not respond to the usual therapies and no H. pylori infection, gastrinoma should be on the list of suspects.

Why Acid Suppression Helps Stop Bleeding

Once an ulcer starts bleeding, the stomach’s own acid works against healing. Gastric acid breaks down blood clots, prevents platelets from clumping together, and activates pepsin, a digestive enzyme that dissolves the fragile clot trying to seal the wound.²⁰ That is why emergency treatment for a bleeding ulcer almost always includes high-dose acid suppression, typically with an intravenous proton pump inhibitor. The goal is to push the stomach’s pH above 6, which is the threshold where clots become stable and platelets can do their job.²¹

Preventing Ulcers When You Cannot Stop the Culprit Drug

Many people cannot simply stop taking NSAIDs or aspirin; the drugs are keeping arthritis manageable or preventing a second heart attack. For these patients, “gastroprotection” means adding a second medication to shield the stomach while the offending drug continues.

A Cochrane review comparing the main options found that proton pump inhibitors (omeprazole, lansoprazole, pantoprazole, and similar drugs) and higher-dose histamine-2 receptor blockers both reduced the risk of NSAID-related ulcers effectively and were generally well tolerated. Misoprostol, a synthetic prostaglandin, was also effective, and it was the only agent shown to reduce actual ulcer complications (not just endoscopic ulcers), but diarrhea and cramping limited how many patients could stick with it.²²

Head-to-head, omeprazole performed at least as well as misoprostol at healing NSAID-related ulcers and was better at keeping them from coming back: about 61% of patients stayed in remission on omeprazole versus 48% on misoprostol.²³ PPIs have become the default gastroprotective drug for this reason, though the choice depends on individual tolerability and risk factors.²⁴

The Emerging Role of Non-H. pylori Stomach Bacteria

For a long time, H. pylori was considered essentially the only bacterium capable of surviving the stomach’s acid bath and causing disease. Newer sequencing technology has upended that assumption. The stomach harbors a diverse microbial community, and when H. pylori is absent, other species fill the niche. In patients with peptic ulcer disease who test negative for H. pylori, researchers have found an enrichment of bacteria typically associated with the mouth, including Neisseria, Porphyromonas, and Alloprevotella, species linked to inflammatory processes that could damage the stomach lining on their own.²⁵

A broader review of the gastric microbiome found that as stomach disease progresses from mild inflammation through precancerous changes, H. pylori often recedes and is replaced by genera like Streptococcus, Prevotella, Lactobacillus, and others. Cases of gastritis with no H. pylori at all showed enrichment of Dialister, Haemophilus, and Treponema, raising the possibility that H. pylori is not the only bacterial player in stomach disease.²⁶ This is early-stage research, and nobody is ready to rewrite treatment guidelines. But it offers a tantalizing explanation for the stubborn minority of ulcers that appear without any obvious cause.

Separately, a study linking specific microbial patterns to gastric cancer risk found that a group enriched with Fusobacterium and Neisseria activated cancer-promoting pathways in stomach cells and drove inflammation in animal models.²⁷ While cancer risk is a separate concern from bleeding ulcers, the finding reinforces the idea that the stomach’s microbial ecology matters in ways we are only beginning to map.

Blood Type, Sex, and Other Host Factors

You will occasionally see claims that blood type O raises your ulcer risk. A cross-sectional study from Ethiopia found that blood group O was more common among ulcer patients than controls, and H. pylori infection rates were highest in the O group, but the association between blood type and ulcer disease did not reach statistical significance.²⁸ The same study did find strong, statistically significant associations with sex (men had about four times the risk), NSAID use, and smoking. So while blood type remains an interesting avenue, the evidence is not strong enough to call it a meaningful risk factor. Being male, using NSAIDs, and smoking are far more robust predictors.