Several common medication classes can cause bowel leakage, either by loosening stool, relaxing the muscles that keep the bowel closed, or reducing your awareness of the urge to go. The most frequently implicated drugs include metformin, SSRIs, antibiotics, weight-loss medications like orlistat, laxatives, magnesium-containing antacids, and certain blood pressure drugs. In many cases, the leakage improves or resolves when the medication is adjusted or stopped.
How Medications Cause Bowel Leakage
Staying continent depends on several things working together: a functioning anal sphincter, firm enough stool, normal bowel motility, and the mental alertness to recognize when you need a bathroom. Medications can disrupt any of these. Some drugs relax the ring of muscle at the end of the rectum, making it harder to hold stool in. Others speed up the gut or pull water into the intestines, producing loose stool that’s much harder to control. A third group, including sedatives and certain psychiatric medications, can dull your awareness of rectal fullness so you don’t respond to the signal in time.
When more than one of these mechanisms overlaps, the risk climbs. Taking a blood pressure drug that relaxes the sphincter alongside an antidepressant that loosens stool, for example, can create a problem that neither drug would cause alone.
Drugs That Relax the Anal Sphincter
The anal sphincter is a muscular valve that stays contracted to prevent leakage. Several cardiovascular and other medications reduce that muscle tone as a side effect:
- Calcium channel blockers, commonly prescribed for high blood pressure and angina
- Nitrates, used for chest pain
- Beta-blockers, another mainstay of blood pressure and heart rate control
- Sildenafil and related erectile dysfunction drugs
- SSRIs (selective serotonin reuptake inhibitors), a widely prescribed class of antidepressants
These medications don’t target the anal sphincter on purpose. They work by relaxing smooth muscle throughout the body, and the sphincter gets caught in the crossfire. You may not notice a problem if your sphincter is strong to begin with, but if there’s any underlying weakness from childbirth, aging, or surgery, the added relaxation can tip the balance toward leakage.
Drugs That Cause Loose or Watery Stool
Even a perfectly healthy sphincter struggles to contain liquid stool. Several medications make stool looser, more urgent, or more frequent.
Metformin
Metformin is the most widely prescribed diabetes medication in the world, and gastrointestinal side effects occur in up to 75% of people who take it. Diarrhea, nausea, bloating, and gas are the most common complaints. In some people the diarrhea is severe enough to cause accidental leakage, especially early in treatment. Notably, these symptoms can also appear years into therapy, not just during the first few weeks.
Orlistat
Orlistat works by blocking fat absorption in the gut. The unabsorbed fat passes through the intestines, producing oily, loose stools. Increased stool frequency, urgency, and anal leakage of oily residue are well-documented effects. This is essentially the drug working as intended, since preventing fat absorption means that fat has to go somewhere.
Antibiotics
Broad-spectrum antibiotics, including penicillins, cephalosporins, and macrolides, disrupt the balance of bacteria in the gut. This can trigger diarrhea directly or, in more serious cases, allow an infection called C. difficile to take hold, which causes profuse watery diarrhea. The disruption to gut bacteria can persist for months or even up to two years after a course of antibiotics, though most antibiotic-related diarrhea resolves within a few weeks of finishing the prescription.
Magnesium-Containing Antacids
Magnesium draws water into the intestines through osmosis. Antacids that contain magnesium hydroxide can soften stool to the point of diarrhea, particularly if taken frequently or in high doses. This is the same mechanism that makes magnesium citrate effective as a laxative.
Laxatives
This one seems obvious, but overuse of laxatives, whether prescription or over-the-counter, is a common and overlooked cause of accidental bowel leakage. Stimulant laxatives in particular can produce unpredictable urgency.
Digoxin
Digoxin, used for certain heart rhythm problems and heart failure, can cause diarrhea as a side effect, particularly when blood levels run high.
SSRIs and Other Antidepressants
SSRIs deserve special mention because they appear in multiple categories. They can relax the anal sphincter, and they also increase serotonin levels in the gut. About 95% of the body’s serotonin is found in the digestive tract, where it plays a major role in regulating motility. When SSRIs block serotonin reuptake, the excess serotonin in the gut can speed up transit and increase the water content of stool.
Among individual SSRIs, sertraline and fluoxetine tend to cause more diarrhea, while paroxetine is more associated with constipation because it slows upper gastrointestinal transit. The SNRI venlafaxine and the newer antidepressant vilazodone also commonly cause diarrhea. These effects are often strongest in the first few weeks of treatment but can persist.
Sedatives and Psychiatric Medications
A different mechanism is at work with sedating drugs. Benzodiazepines, tricyclic antidepressants, and antipsychotics can all reduce alertness enough that you don’t recognize or respond to the sensation of rectal fullness in time. This is particularly relevant at night or for people who are already cognitively impaired. The bowel itself may be functioning normally, but the brain’s ability to process the signal and get to a bathroom is compromised.
GLP-1 Receptor Agonists
The newer class of weight-loss and diabetes medications, including semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound), has been linked to a range of gastrointestinal functional disorders. A large study published in the American Journal of Gastroenterology found that people taking GLP-1 receptor agonists had a 32% higher prevalence of fecal incontinence compared to those not on these drugs. They also had higher rates of functional diarrhea and various forms of irritable bowel syndrome. Given how rapidly prescriptions for these drugs have increased, this is a side effect worth knowing about.
Why Older Adults Face Higher Risk
Polypharmacy, defined as taking multiple medications simultaneously, is one of the strongest predictors of fecal incontinence in older adults regardless of gender. A cross-sectional study of elderly outpatients found that polypharmacy was a significant independent risk factor for bowel leakage in both men and women. This makes sense: the more medications you take, the more likely you are to be on at least one that loosens stool and another that relaxes the sphincter or dulls awareness. Age-related changes to the pelvic floor and sphincter muscles compound the problem, meaning a drug that causes no issues for a 40-year-old can cause significant leakage for a 75-year-old.
What You Can Do About It
If you suspect a medication is causing bowel leakage, the most important step is identifying which drug is responsible. Look at the timing: did the problem start when a new medication was added or a dose was increased? Keeping a brief diary of symptoms alongside your medication schedule can make this much clearer.
Medication-related bowel leakage is often manageable without stopping the drug entirely. Options include adjusting the dose, switching to a different medication in the same class (for example, swapping one SSRI for another with fewer GI effects), or changing when you take the medication relative to meals. For metformin, an extended-release formulation causes significantly less diarrhea than the standard version.
In some cases, over-the-counter anti-diarrheal agents like loperamide can help. Loperamide works by slowing bowel motility and firming up stool, and it also appears to increase anal sphincter muscle tone, which directly counteracts the mechanism behind several of the medications listed above. Soluble fiber supplements can also help by absorbing excess water in the intestines and giving stool more bulk and form.
For people on multiple medications, a pharmacist-led medication review can identify which combinations are most likely contributing to the problem and suggest alternatives. This is especially valuable for older adults managing several chronic conditions at once.