Can losartan raise ALT levels? Separating fact from rare risk

October 10, 2025 •

4 min read

Losartan is a widely prescribed angiotensin II receptor blocker for hypertension, with a reported incidence of minor liver enzyme elevations of less than 2% during clinical trials. While generally considered safe, the potential for drug-induced hepatotoxicity is a rare but documented risk, leading many to ask: Can losartan raise ALT levels?

Quick Summary

Losartan can cause rare, transient elevations in ALT and other liver enzymes. While severe liver injury is extremely uncommon, patients should be aware of this idiosyncratic risk, especially during early treatment. Monitoring is key, and discontinuing the drug typically resolves the issue. In contrast, it may improve liver function in chronic liver conditions like NAFLD.

Key Points

Rare Side Effect: Losartan is rarely associated with elevated ALT levels, with clinical trial data showing the incidence is often no higher than with a placebo.
Idiosyncratic Reaction: Severe liver injury from losartan is an unpredictable, idiosyncratic reaction, not a dose-dependent effect.
Positive Liver Effects: In some patients with conditions like NAFLD, losartan has demonstrated a beneficial, anti-fibrotic effect and can help lower ALT levels.
Timing of Injury: When DILI does occur, it typically manifests within 1 to 8 weeks after starting losartan therapy.
Discontinuation is Key: If losartan is identified as the cause of liver injury, discontinuing the medication is the first step and usually leads to recovery of liver function.
Re-challenge Risk: Re-exposure to losartan after experiencing liver injury can lead to a more severe reaction and should be avoided.
Vigilant Monitoring: Patients with pre-existing liver conditions or who are otherwise high-risk should receive regular monitoring of liver enzymes.

Understanding Losartan and Liver Function

Losartan is a widely used medication belonging to a class of drugs known as angiotensin II receptor blockers (ARBs). It works by blocking the action of angiotensin II, a chemical that narrows blood vessels, thereby helping to lower blood pressure. Losartan is generally well-tolerated, but like all medications, it carries a risk of side effects, including potential effects on the liver. The liver plays a crucial role in drug metabolism, so its function can be affected by many different medications, though often rarely.

Alanine aminotransferase (ALT) is an enzyme primarily found in liver cells. When the liver is damaged, it releases ALT into the bloodstream, causing elevated blood levels. For this reason, monitoring ALT levels is a standard part of assessing liver health.

The Link Between Losartan and Elevated ALT

While Losartan is not a common cause of liver problems, it has been associated with rare instances of drug-induced liver injury (DILI). The overall incidence of elevated serum aminotransferase (including ALT) levels is reported to be very low, often less than 2% in controlled trials. In these cases, the elevation is frequently transient and mild, resolving on its own without needing a change in medication.

However, there have been case reports of more severe liver injury attributed to losartan. The onset of this hepatotoxicity is often unpredictable and idiosyncratic, meaning it is not dose-dependent and resembles a hypersensitivity reaction. The mechanism of injury is not fully understood but may involve genetic factors affecting the drug's metabolism. For patients with underlying liver disease, or those with other risk factors, vigilance is especially important.

Clinical Presentation of Losartan-Induced Liver Injury

In reported cases of DILI due to losartan, the onset typically occurs within 1 to 8 weeks of starting the medication. Symptoms can include:

Jaundice (yellowing of the skin or eyes)
Unexplained fatigue and weakness
Nausea or vomiting
Abdominal pain, particularly in the upper right quadrant
Dark urine or pale stools

Different patterns of liver injury can be observed, including hepatocellular (most common), cholestatic, or a mix of both. The type of injury influences the pattern of elevated liver enzyme levels, but in all cases, the primary course of action is discontinuing the drug if it is deemed the cause.

Potential Protective Effects on the Liver

Counterintuitively, some research suggests that losartan may offer protective benefits for certain liver conditions. This is particularly noted in patients with non-alcoholic fatty liver disease (NAFLD) and chronic hepatitis C (HCV). The underlying mechanism involves the drug's ability to inhibit hepatic stellate cells, which are key drivers of liver fibrosis.

Studies have shown that losartan can have an antifibrotic effect, potentially leading to regression of liver fibrosis and improved liver function. For example, a meta-analysis found that losartan could significantly lower ALT levels in patients with NAFLD. This dual potential — rare adverse effect versus potential therapeutic benefit in specific contexts — underscores the importance of careful patient evaluation and monitoring.

Management and Monitoring of Liver Enzymes

Given the rare but possible risk of liver injury, monitoring is crucial, particularly when initiating therapy or for patients with pre-existing liver conditions. Monitoring involves a combination of patient vigilance and regular laboratory tests.

Regular Lab Work: Routine liver function tests, including ALT, AST, and bilirubin, are recommended, especially for high-risk patients.
Symptom Awareness: Patients should be educated on the symptoms of hepatotoxicity and report them to their doctor immediately.
Prompt Action: If liver injury is suspected, the first step is to discontinue losartan. In many cases, liver enzymes return to normal within a few weeks to months.
Re-challenge Caution: Re-exposure to losartan after a DILI episode is discouraged, as it can lead to a more severe and dangerous reaction.

Losartan vs. Other Angiotensin Receptor Blockers

Not all ARBs carry the same profile regarding liver effects. While rare cases of DILI have been reported across the class, the incidence and specific risks can differ. The following table provides a comparison based on available information:


Feature	Losartan	Valsartan	Irbesartan	Olmesartan
Liver Injury Risk	Rare, but documented DILI cases	Rare DILI cases reported	Rare DILI cases reported	Possibly lower risk, no specific cases yet but theoretically possible
Hepatocellular Injury	Reported, often acute hepatitis-like	Reported	Reported	Not specifically linked to cases
Cholestatic/Mixed Injury	Reported	Reported	Reported	Reported
Onset Time	Typically within 1-8 weeks	Can vary widely	Typically within 1-8 weeks	Can vary, linked to enteropathy-related fatty liver
Associated Enteropathy	Rare instances of sprue-like enteropathy reported	Implicated in rare instances	Implicated in rare instances	Most common association with sprue-like enteropathy

Conclusion: Navigating the Low Risk

For the vast majority of patients, losartan is a safe and effective medication for controlling blood pressure, with liver toxicity being an exceedingly rare adverse effect. However, the potential for an idiosyncratic reaction leading to elevated ALT levels and more significant liver injury exists, and it is a risk that healthcare providers and patients should be aware of. In certain cases, losartan can even have a positive effect on liver enzyme levels and fibrosis in patients with pre-existing conditions like NAFLD.

Patient awareness of early signs of liver injury and adherence to monitoring recommendations, especially for those with existing liver disease, are paramount for safe usage. Should unexplained symptoms arise, or blood tests indicate significant liver enzyme elevation, a medical professional can evaluate the cause and determine the appropriate course of action. For more detailed information on drug-induced liver injury, you can consult reliable resources such as the NIH's LiverTox database.

Frequently Asked Questions

No, it is not common. The overall incidence of elevated serum aminotransferase levels, including ALT, due to losartan is low, reported to be less than 2% in clinical trials and sometimes similar to rates observed with a placebo.

DILI linked to losartan is a very rare adverse reaction where the medication causes liver damage. This is often an idiosyncratic reaction, meaning it is not dose-dependent and its occurrence is unpredictable.

In the rare event of liver injury, symptoms may include jaundice (yellowing of the skin or eyes), unexplained fatigue, nausea, vomiting, abdominal pain, or dark urine.

You should contact your doctor immediately. If a doctor confirms losartan is the likely cause, the medication will be discontinued. Do not stop taking the medication on your own without professional medical advice.

For most patients, routine blood tests are sufficient. However, for those with pre-existing liver disease or other risk factors, closer monitoring of liver function tests, such as ALT, may be recommended.

In some cases, yes. Losartan has shown protective, anti-fibrotic effects in patients with chronic liver diseases like non-alcoholic fatty liver disease (NAFLD), and in some studies, has been found to help lower ALT levels.

While rare cases of liver injury have been reported with several ARBs, including Valsartan and Irbesartan, the risk profile can vary. A case report suggested a potentially lower risk with Olmesartan, but more data is needed.

Yes. In reported cases where liver injury was attributed to losartan, the liver enzyme levels typically returned to normal within a few weeks to months after the medication was discontinued.