Aspirin can contribute to constipation, though it does so less dramatically than the drugs most people associate with that side effect. A community-based study found that regular aspirin users had roughly 70 percent higher odds of reporting chronic constipation compared to non-users, an effect that sits in the same range as other common pain relievers like ibuprofen. Most people know aspirin for its upper-GI reputation, the stomach upset and bleeding risk, so the constipation link tends to catch users off guard.
What the Research Actually Found
The clearest data on aspirin and constipation comes from a study of over 500 adults without irritable bowel syndrome, where about 18 percent reported chronic constipation. Among the factors examined, aspirin use was significantly linked to constipation, with an odds ratio of 1.7. That means aspirin users were roughly 1.7 times as likely to have chronic constipation as non-users. For context, acetaminophen users who took seven or more tablets per week had even higher odds, at 2.7, while other non-steroidal anti-inflammatory drugs (NSAIDs) came in at 1.8.1PubMed. Risk factors for chronic constipation and a possible role of analgesics The study found no significant connection between constipation and factors like age, gender, body mass index, smoking, coffee intake, or stress. The analgesic connection stood out.
A separate community survey of NSAID users reinforced this pattern. Lower-bowel symptoms, particularly constipation and straining, were more common among people taking NSAIDs (including aspirin) than in controls. In fact, constipation was a more common reason for stopping medication than dyspepsia, which is the upper-GI discomfort that tends to dominate safety discussions about these drugs.2International Journal of Clinical Practice. Gastrointestinal Side-Effects of NSAIDs in the Community That finding is worth sitting with: people were more likely to quit their pain reliever over constipation than over stomach pain.
A large Danish population-based study also categorized aspirin and NSAIDs among medications known to induce constipation, grouping them alongside opioids, calcium channel blockers, and anticholinergic drugs.3BMJ Journals. Constipation and risk of cardiovascular diseases: a Danish population-based matched cohort study So while aspirin doesn’t carry a bold constipation warning the way opioids do, the medical literature does recognize it as a contributor.
Why Aspirin Might Slow Things Down
Aspirin works by blocking enzymes called cyclooxygenases, known as COX-1 and COX-2. These enzymes produce prostaglandins, which serve as chemical messengers throughout the body. In the gut, prostaglandins do more than just protect the stomach lining from acid. They also play a direct role in how the smooth muscle of the intestines contracts and propels food along.
Research in animal models has shown this relationship clearly. When COX-2 activity ramps up, levels of prostaglandin E2 rise, and that prostaglandin actually decreases colonic smooth muscle contractility by acting through specific receptor types called EP2 and EP4. In a healthy gut, prostaglandins working through a different pair of receptors (EP1 and EP3) help maintain normal contractions. Blocking the whole system with a COX inhibitor disrupts this balance.4PubMed Central. Prophylactic and therapeutic benefits of COX-2 inhibitor on motility dysfunction in bowel obstruction: roles of PGEâ‚‚ and EP receptors The upshot is that aspirin’s interference with prostaglandin production can alter the rhythmic muscular contractions that move material through the colon. Slowed motility means the colon absorbs more water from stool, making it harder and more difficult to pass.
This mechanism is shared with other NSAIDs like ibuprofen and naproxen, which explains why the constipation signal in research isn’t unique to aspirin. Any drug that broadly suppresses prostaglandin synthesis has the potential to slow the gut.
The Upper-GI Reputation Overshadows Lower-GI Effects
When clinicians and patients think about aspirin’s effect on the digestive system, stomach ulcers and bleeding come to mind first. That reputation is well earned. A pooled analysis of randomized trials found that the risk of upper-GI symptoms with aspirin had an odds ratio of about 1.7, while GI bleeding risks ranged between 1.5 and 2.0.5PubMed Central. The gastrointestinal toxicity of aspirin: an overview of randomised controlled trials Fatal bleeds were rare, but the upper-GI picture dominates clinical conversations.
Aspirin also affects the small intestine. Capsule endoscopy studies in healthy volunteers have shown that even short-term use of low-dose aspirin can cause mild mucosal inflammation in the small bowel, while chronic use produces a wider range of lesions, from tiny hemorrhages and erosions to frank ulcers.6PubMed. Small bowel injury in low-dose aspirin users This small-bowel injury is sometimes called aspirin enteropathy, and it can cause subtle symptoms like bloating, cramps, or changes in bowel habits that users might not immediately connect to their aspirin.
Because the upper-GI risks are more dramatic and more studied, constipation has historically received less attention in both drug labeling and clinical conversations. The FDA adverse event reporting system’s top 30 drugs most associated with constipation are dominated by cancer drugs, immunomodulators, and a few other medication classes, and aspirin doesn’t appear among them.7PubMed Central. Exploring the top 30 drugs associated with drug-induced constipation based on the FDA adverse event reporting system That doesn’t mean aspirin doesn’t cause constipation; it means the effect is modest enough not to rank alongside heavy hitters like lenalidomide or opioids in formal adverse-event databases. For someone experiencing it, though, the frequency rankings are cold comfort.
How Aspirin Compares to Other Common Pain Relievers
If you’re deciding between analgesics and worried about constipation, the landscape looks roughly like this: opioid painkillers are in a league of their own, causing constipation in a large fraction of users through a completely different mechanism that directly paralyzes gut motility. Non-opioid analgesics all carry some constipation risk, but the magnitudes differ.
Acetaminophen, at seven or more tablets per week, showed the strongest association with chronic constipation among the non-opioid painkillers studied, with odds roughly 2.7 times higher than non-users. Aspirin and other NSAIDs fell in a similar band, around 1.7 to 1.8 times.1PubMed. Risk factors for chronic constipation and a possible role of analgesics These are all modest elevations in risk compared to opioids, but they’re not trivial for someone taking the medications daily.
One interesting wrinkle from community data: there were no meaningful differences in upper-GI symptom rates between people taking aspirin and those taking other individual NSAIDs.2International Journal of Clinical Practice. Gastrointestinal Side-Effects of NSAIDs in the Community The GI effects of these drugs track together more than drug labels would suggest. Switching from aspirin to ibuprofen for constipation relief, in other words, probably won’t help much.
Does Enteric Coating Help With Constipation?
Enteric-coated aspirin was designed to bypass the stomach entirely. The tablet is wrapped in a cellulose or silicon layer that resists dissolving in stomach acid and instead breaks down in the more alkaline environment of the upper small intestine. Buffered formulations take a different approach, using compounds like calcium carbonate or magnesium oxide to neutralize acid around the tablet.8PubMed Central. Enteric-Coated Aspirin and the Risk of Gastrointestinal Side Effects: A Systematic Review
These formulations are aimed at reducing stomach irritation and ulcer risk. They do not change the systemic prostaglandin-blocking effect that drives constipation. Once aspirin is absorbed into the bloodstream, regardless of where in the gut it dissolved, it still inhibits COX enzymes throughout the body, including in the intestinal smooth muscle. So if your constipation is related to aspirin’s effect on gut motility rather than local stomach irritation, switching to an enteric-coated version is unlikely to resolve it. The coating solves a different problem.
Buffered formulations containing magnesium, on the other hand, could theoretically have a slight offsetting effect, since magnesium itself acts as an osmotic laxative that draws water into the intestine. But the amount of magnesium in a buffered aspirin tablet is small, and relying on it as a constipation remedy would be optimistic.
Older Adults Face a Double Burden
Elderly people are the population most likely to take aspirin daily, typically as a low-dose antiplatelet therapy for cardiovascular protection, and they’re also the population most prone to constipation for other reasons. Reduced physical activity, lower fluid intake, decreased dietary fiber, and the use of multiple medications all converge in older adults. A study of elderly patients found that NSAID and low-dose aspirin users had significantly higher rates of upper-GI symptoms compared to non-users.9SpringerLink / Drugs & Aging. NSAID and aspirin use by the elderly in general practice: effect on gastrointestinal symptoms and therapies
What makes older adults particularly vulnerable to aspirin-related constipation is the stacking effect. If you’re already on a calcium channel blocker for blood pressure, a diuretic for fluid retention, and aspirin for your heart, you have three medications that can each slow the gut. Individual risk from any one drug may be modest, but the cumulative effect can be meaningful. Clinicians sometimes overlook this because each drug’s constipation risk seems low in isolation.
If you’re an older adult on daily aspirin who develops new or worsening constipation, the aspirin is worth mentioning to your doctor, but so is every other medication in the lineup. The culprit may be the combination rather than any single pill.
What About Alternatives Like Clopidogrel?
For people who need antiplatelet therapy but find aspirin’s GI effects intolerable, clopidogrel is the most common alternative. Data from the large CAPRIE trial showed that clopidogrel had significantly fewer gastrointestinal adverse events than aspirin overall, with rates of about 27 percent versus 30 percent. The difference included less constipation specifically, along with less abdominal pain, dyspepsia, and ulceration.10PubMed. Comparative safety and tolerability of clopidogrel and aspirin: results from CAPRIE
Clopidogrel works through an entirely different mechanism. Instead of blocking COX enzymes and prostaglandins, it inhibits a receptor on platelets that’s involved in clot formation. Because it doesn’t suppress prostaglandin production in the gut, it sidesteps the motility issue that aspirin creates. That said, the decision to switch from aspirin to clopidogrel involves weighing cardiovascular efficacy, bleeding risk, cost, and side-effect profile, and it’s not a decision to make on your own just to ease constipation. But it’s useful to know that less constipating antiplatelet options exist.
Aspirin Changes the Gut Microbiome
An area of active research is how aspirin affects the community of bacteria living in the intestines. A randomized trial comparing daily aspirin at 325 milligrams to placebo found measurable shifts in microbial composition over the study period. Four bacterial groups differed significantly between the aspirin and placebo arms, and among bacteria previously linked to colorectal cancer or aspirin intake, aspirin appeared to increase the relative abundance of certain groups like Akkermansia and Prevotella while decreasing others like Bacteroides and Parabacteroides.11PubMed Central. Randomised clinical study: oral aspirin 325 mg daily vs placebo alters gut microbial composition and bacterial taxa associated with colorectal cancer risk
Whether these microbiome shifts contribute to constipation, or protect against it, or do something else entirely, is still an open question. The study was designed to investigate aspirin’s well-known association with reduced colorectal cancer risk, not bowel habits. But the gut microbiome is deeply involved in stool consistency and transit time, so the finding raises intriguing questions. Some of the bacteria that increased with aspirin, like Akkermansia, are generally considered beneficial for gut health. Others, like the shifts in Prevotella, have more ambiguous implications depending on the person’s overall microbial landscape.
This research is early-stage and shouldn’t change anyone’s decision about taking aspirin. But it adds a layer to understanding why aspirin’s effects on the gut go well beyond the simple “stomach irritation” story.
Practical Steps If You Suspect Aspirin Is the Cause
Before attributing constipation to aspirin, it helps to rule out more common causes. Inadequate fluid intake, low fiber, sedentary habits, and other medications are responsible for the vast majority of constipation cases. If you’ve recently started aspirin or increased your dose and noticed a change in bowel habits, the timing matters. Drug-related constipation typically begins within days to a few weeks of starting or dose-adjusting the medication.
If aspirin is a likely contributor and you’re taking it for pain relief rather than heart protection, the simplest approach is to try a different analgesic class, though as the evidence shows, switching to acetaminophen may actually make things worse. If you’re taking daily low-dose aspirin for cardiovascular prevention, do not stop it without talking to your doctor. The cardiovascular stakes of stopping antiplatelet therapy abruptly can be serious.
Standard constipation management applies here as much as anywhere: increasing fiber gradually, staying well-hydrated, and adding physical activity can all help counteract the motility-slowing effects of aspirin. Osmotic laxatives like polyethylene glycol are generally safe to take alongside aspirin if dietary changes aren’t enough. Stimulant laxatives work too but aren’t ideal for long-term daily use. Your pharmacist can help you pick something that won’t interact with your other medications.
The Combination Product Trap
Many over-the-counter products combine aspirin with other ingredients, and some of those additions carry their own constipation risk. Aspirin-caffeine combinations are common in headache remedies, and while caffeine itself tends to stimulate the gut, the net effect varies. More relevant is the pairing of aspirin with codeine or other opioids in prescription combination analgesics. If you’re taking a product that includes both aspirin and an opioid, the opioid component is almost certainly driving any constipation far more than the aspirin is.
Antacids co-formulated with aspirin can also be relevant. Aluminum-containing antacids are known to cause constipation, while magnesium-based ones tend toward the opposite. Reading the inactive ingredients on the label is worth the thirty seconds it takes if constipation has become a recurring problem.
People often think of “aspirin” as a single, uniform substance, but what you actually swallow can vary quite a bit depending on the brand and formulation. When troubleshooting constipation, the full ingredient list matters more than the product name on the box.