What Is Losartan?
Losartan, often sold under the brand name Cozaar, is an angiotensin II receptor blocker (ARB) used primarily to treat high blood pressure (hypertension). By blocking the action of angiotensin II, a hormone that narrows blood vessels, losartan helps to relax and widen them. This allows blood to flow more smoothly and reduces the workload on the heart.
Losartan is also prescribed for other conditions, such as reducing the risk of stroke in patients with hypertension and left ventricular hypertrophy and managing kidney disease in those with type 2 diabetes. It is a very common and generally well-tolerated medication, but like all drugs, it can have side effects.
The Connection to Sprue-Like Enteropathy
The question "Does losartan cause malabsorption?" is rooted in a discovery made several years ago involving another ARB, olmesartan (Benicar). Researchers at the Mayo Clinic identified a link between olmesartan and a severe gastrointestinal condition known as sprue-like enteropathy (SLE). This condition is characterized by intestinal malabsorption, chronic diarrhea, and significant weight loss, often accompanied by changes in the intestinal lining that closely resemble celiac disease.
Is Malabsorption a Losartan-Specific Risk or a Class Effect?
While olmesartan was the first ARB definitively linked to SLE, subsequent case reports and observational studies have suggested that this severe side effect may be a "class effect," meaning it could potentially be caused by any drug in the ARB family. Reports have emerged detailing cases of enteropathy associated with other ARBs, including losartan, valsartan, and irbesartan.
For example, a case report in 2017 highlighted the first known instance of losartan-induced enteropathy, where a patient with chronic diarrhea and weight loss saw complete resolution of symptoms and reconstruction of intestinal villi after stopping the medication. Another case detailed losartan-associated sprue-like enteropathy presenting uniquely as anemia without typical GI symptoms, which also resolved upon drug cessation. These findings suggest that while the incidence of ARB-induced enteropathy is relatively low across the class, losartan is not exempt from this potential risk.
Symptoms and Diagnosis of ARB-Induced Malabsorption
Diagnosing ARB-induced enteropathy can be challenging because its symptoms and histological features often mimic celiac disease. Common symptoms include:
- Severe, chronic diarrhea
- Significant, unexplained weight loss
- Abdominal pain or discomfort
- Nausea and vomiting
- Fatigue
- Anemia, which can sometimes occur even without overt gastrointestinal symptoms
Key diagnostic clues for ARB-induced enteropathy include the fact that blood tests for celiac disease (such as anti-tissue transglutaminase antibodies) are typically negative, and unlike celiac disease, the condition does not respond to a gluten-free diet. Endoscopic findings usually show villous atrophy in the small intestine, a key sign of malabsorption. Critically, a patient's symptoms and intestinal damage resolve after they stop taking the ARB.
Losartan's Other Gastrointestinal Side Effects
It is important to differentiate this rare but severe sprue-like enteropathy from the more common and milder gastrointestinal side effects associated with losartan. While malabsorption is exceptionally rare, losartan can cause other GI issues that are generally more manageable. These include:
- Mild diarrhea
- Stomach pain or abdominal discomfort
- Nausea
- Indigestion or heartburn
- Constipation
What to Do if You Suspect Malabsorption
If you are taking losartan and experience persistent and severe gastrointestinal issues such as chronic diarrhea and unexplained weight loss, it is crucial to speak with your healthcare provider immediately. Do not stop taking your medication on your own, as this can have serious consequences for your blood pressure. Your doctor will evaluate your symptoms and history, potentially order diagnostic tests, and may consider switching you to an alternative medication if an ARB-induced enteropathy is suspected.
Comparison of ARB Gastrointestinal Side Effects
| Feature | Losartan | Olmesartan | Other ARBs (Valsartan, Irbesartan, etc.) |
|---|---|---|---|
| Associated Malabsorption | Yes (rare case reports) | Yes (initially documented, more prevalent reports) | Yes (rare case reports) |
| Sprue-like Enteropathy Risk | Very low, considered a class effect | Documented association, known risk | Very low, considered a class effect |
| Common GI Side Effects | Nausea, mild diarrhea, abdominal pain | Nausea, mild diarrhea, abdominal pain | Nausea, mild diarrhea, abdominal pain |
| Typical Onset of Enteropathy | Can be delayed, months to years after starting | Can be delayed, months to years after starting | Can be delayed, months to years after starting |
| Resolution | Symptoms resolve upon discontinuation | Symptoms resolve upon discontinuation | Symptoms resolve upon discontinuation |
The Impact on Nutrient Absorption (Beyond Malabsorption)
Beyond the rare risk of severe enteropathy, some studies have noted more specific effects on nutrient metabolism. For instance, research from 2005 indicated that losartan treatment can cause an increase in urinary zinc excretion, potentially leading to zinc deficiency in hypertensive patients. This is a distinct metabolic effect and not directly caused by intestinal malabsorption. Patients taking a combination of losartan and hydrochlorothiazide showed an additive effect on urinary zinc losses. However, the same study found no significant impact on magnesium or nitric oxide metabolism.(https://www.sciencedirect.com/science/article/abs/pii/S0895706104010568)
Conclusion: Losartan and Malabsorption Risk
While it is extremely rare, the answer to the question "Does losartan cause malabsorption?" is yes, it can, as part of a recognized adverse effect called sprue-like enteropathy. This condition is not common but can cause severe symptoms like chronic diarrhea, weight loss, and intestinal damage. It is a class-wide risk for ARBs, though it was initially and most prominently associated with olmesartan. The key takeaway for patients is that if they develop persistent and severe gastrointestinal symptoms while on losartan, they should consult their doctor. The good news is that if ARB-induced enteropathy is the cause, the symptoms and intestinal damage are typically reversible upon discontinuing the medication.
This highlights the critical importance of a thorough medical history for patients on ARBs who present with unexplained gastrointestinal issues, allowing healthcare providers to consider drug-induced enteropathy as a potential cause and prevent unnecessary testing for other conditions like celiac disease.
