Yes, lisinopril can cause diarrhea, but it is one of the least common gastrointestinal side effects of the drug, reported in roughly 2% to 3% of patients in clinical trials compared with about 10% to 20% for cough. The diarrhea is usually mild, watery, and dose-related, appearing within the first two weeks of therapy or after a dose increase. However, any new diarrhea on lisinopril deserves a careful look, because a small number of cases reflect serious problems, including intestinal angioedema, that require stopping the drug immediately.
How an ACE inhibitor reaches your gut
Lisinopril blocks the angiotensin-converting enzyme, or ACE. That enzyme does two jobs: it converts angiotensin I into angiotensin II, a powerful vessel-constricting hormone, and it breaks down bradykinin, a peptide that promotes inflammation and fluid leakage. Blocking ACE lowers blood pressure, which is the therapeutic goal. It also lets bradykinin accumulate, which is the source of most lisinopril side effects.
Bradykinin does not stay in the bloodstream. It acts locally on tissue, and the intestinal wall has plenty of ACE and bradykinin receptors. When bradykinin rises in the gut lining, it increases blood flow to the intestine and makes the mucosal capillaries leakier. That shifts fluid into the bowel lumen and speeds transit. In plain terms: the same chemical buildup that causes the classic dry cough can irritate the intestine and loosen stool.
A second mechanism involves prostaglandins. ACE inhibition raises local prostaglandin production, and prostaglandins stimulate intestinal secretion and motility. A third, less certain pathway involves changes in gut bacteria and bile acid handling, which some researchers suspect but have not confirmed in controlled studies. The bradykinin pathway is the best established, and it explains why diarrhea tends to track with dose and with a person's individual sensitivity to ACE inhibitors.
How common is it, really?
The placebo-controlled trials behind lisinopril's approval put diarrhea among the reported adverse events at roughly 2% to 3% of treated patients. That figure is close to placebo in most of those trials, which means many cases attributed to the drug are coincidental. The number matters because it reframes the question: lisinopril is a plausible but uncommon cause of diarrhea, not a leading one.
| Side effect | Approximate incidence on lisinopril | Typical timing | Mechanism |
|---|---|---|---|
| Dry cough | 10% to 20% | 1 to 6 weeks | Bradykinin buildup in airways |
| Diarrhea | 2% to 3% | 1 to 14 days, or after dose rise | Bradykinin and prostaglandins in gut |
| Dizziness | 3% to 5% | First week | Blood pressure drop |
| High potassium | 1% to 3% | Weeks to months | Reduced aldosterone |
| Angioedema | 0.1% to 0.7% | Hours to years | Bradykinin-driven swelling |
Lisinopril is one of the most prescribed blood pressure drugs in the United States, with tens of millions of prescriptions written each year, so even a 2% rate translates into a large absolute number of people who will notice loose stools after starting it. That arithmetic is why the symptom shows up often in forums even though it is statistically uncommon.
The timeline: when diarrhea appears and when it stops
Most lisinopril-related diarrhea clusters in the first two weeks. A smaller group develops it after a dose increase, and a rare group develops it months or years into therapy, usually in the context of intestinal angioedema.
| Time after starting or changing dose | What tends to happen | What it suggests |
|---|---|---|
| Day 1 to 3 | Mild loose stools, often with dizziness | Blood pressure effect, possibly dose too high |
| Day 4 to 14 | Watery diarrhea, cramping | Most likely bradykinin-related drug effect |
| Week 2 to 6 | Diarrhea persists or resolves | If it persists, discuss alternatives |
| 1 to 3 months | New diarrhea after a stable period | Consider other causes first |
| Months to years | Recurrent cramping and diarrhea | Possible intestinal angioedema, rare |
| Within 48 hours of stopping | Symptoms ease | Supports drug as the cause |
The practical takeaway from the timeline: if diarrhea starts within the first two weeks and improves within two days of stopping the drug, the link to lisinopril is strong. If it starts after a year of stable use, the drug is far less likely to be responsible.
Variations and edge cases that change the picture
Dose matters. Higher lisinopril doses, typically 20 mg to 40 mg daily, produce more bradykinin accumulation than the 5 mg to 10 mg starting range. Patients who develop diarrhea at 40 mg sometimes tolerate 10 mg without symptoms.
Genetic variation matters too. People of African ancestry have a higher rate of ACE inhibitor cough, roughly two to four times the rate seen in people of European ancestry, and the same bradykinin sensitivity is thought to raise the risk of gut symptoms. A 2023 review of ACE inhibitor intolerance noted that this population difference is one of the most consistent findings in the field.
Combination therapy matters. Lisinopril is often paired with a thiazide diuretic such as hydrochlorothiazide. Thiazides themselves can cause diarrhea, and the combination can produce symptoms that neither drug causes alone. If diarrhea starts after switching from lisinopril alone to lisinopril plus a diuretic, the diuretic is a reasonable suspect.
Age and kidney function matter. Older adults and people with reduced kidney function clear lisinopril more slowly, which can amplify bradykinin effects. Kidney function also determines the starting dose, and a dose that is appropriate for normal kidneys can be too high when the estimated glomerular filtration rate falls below 30.
The non-obvious risk: intestinal angioedema
The most important caveat is not the common diarrhea. It is a rare condition called intestinal angioedema, in which bradykinin causes deep swelling in the wall of the intestine. It affects an estimated 0.1% to 0.3% of ACE inhibitor users, appears more often in women, and can strike months or years after the drug was started, long after the patient and clinician have stopped thinking about it.
Intestinal angioedema presents as severe abdominal pain, vomiting, and watery diarrhea, sometimes with facial or lip swelling. Imaging may show bowel wall thickening. Because it mimics gastroenteritis, appendicitis, or inflammatory bowel disease, patients are sometimes admitted and even operated on before the drug link is recognized. The treatment is to stop the ACE inhibitor; symptoms usually resolve within 24 to 72 hours. The key clinical rule is that anyone on an ACE inhibitor who develops severe abdominal pain with vomiting or diarrhea should have the drug stopped while other causes are investigated.
Common misconceptions, corrected
The first misconception is that lisinopril is a common cause of diarrhea. It is not. The 2% to 3% trial rate is close to placebo, and most diarrhea in people taking lisinopril has an ordinary cause such as a viral infection, a new food, or another medication.
The second misconception is that the diarrhea means an allergy. True allergy to lisinopril is rare and presents as hives, facial swelling, or breathing difficulty, not isolated loose stools. Diarrhea on lisinopril is a pharmacological side effect, not an immune reaction.
The third misconception is that stopping the drug is the only option. Many patients do well on a lower dose, and some tolerate a different ACE inhibitor such as enalapril at an equivalent dose. Others are switched to an angiotensin receptor blocker, or ARB, which does not raise bradykinin and therefore very rarely causes cough or diarrhea. ARBs include losartan, valsartan, and olmesartan. ARBs are not a perfect substitute in every case, and the choice depends on why lisinopril was prescribed, but they are the standard alternative when ACE inhibitor intolerance is the problem.
The fourth misconception is that the diarrhea is harmless and can be ignored. Usually it is harmless. But dehydration, electrolyte loss, and kidney strain from prolonged diarrhea are real risks, especially in older adults and in people already taking a diuretic.
What to actually do
If you are taking lisinopril and develop diarrhea, the following steps are the practical ones.
- Track the timing. Note the date diarrhea started relative to your last dose change. A start within two weeks of beginning lisinopril or a dose increase is meaningful evidence.
- Check for red flags and seek care promptly if any appear: severe abdominal pain, vomiting that prevents fluids, blood in stool, fever above 101 F, facial or lip swelling, or lightheadedness on standing.
- Do not stop the drug on your own without a plan. Call your prescriber. In most cases the drug can be paused for a few days and symptoms reassessed.
- Rehydrate with an oral rehydration solution rather than plain water, and avoid high-sugar drinks that can worsen diarrhea.
- Review other medications with your pharmacist. Diuretics, metformin, and some antibiotics can cause diarrhea, and the timing may point to one of them instead.
When you speak with your clinician, bring the specific numbers: when diarrhea started, how many episodes per day, whether it is watery or bloody, and whether it improves when the drug is paused. That information determines whether the next step is a dose reduction, a switch to an ARB, or a workup for another cause.
Limitations of the evidence
Most of what is known about lisinopril and diarrhea comes from pre-approval trials and post-marketing reports, not from dedicated studies. The pre-approval trials were designed to detect blood pressure effects and major adverse events, not to characterize diarrhea, and their 2% to 3% figures have wide confidence intervals. Post-marketing reports are voluntary and biased toward unusual or severe cases, so they overstate the rare risks.
There has never been a large randomized trial comparing diarrhea rates between lisinopril and placebo over long periods. The mechanism linking bradykinin to intestinal symptoms is well supported by physiology and by the parallel with ACE inhibitor cough, but the direct evidence in the gut is thinner than the evidence in the airway. That means the honest answer is that lisinopril can cause diarrhea through a plausible, partly confirmed mechanism, but the exact frequency in everyday use is uncertain and likely lower than online reports suggest.
For anyone weighing whether to stay on lisinopril, the decision should rest on the balance of benefits and side effects with a clinician who knows your blood pressure, kidney function, and other medications. The drug remains a first-line treatment for high blood pressure and heart failure, and mild diarrhea that resolves on its own is not a reason to abandon it. Persistent, severe, or red-flag diarrhea is a reason to call promptly and consider an alternative.