Common and Serious Nintedanib Side Effects

Diarrhea is by far the most common side effect of nintedanib, affecting roughly two-thirds of people who take it in clinical trials, and it is the reason most patients need a dose change or temporary break from the drug. Beyond the gut, the serious side effects that matter most are liver injury, cardiovascular events, bleeding, and a rare but dangerous risk of gastrointestinal perforation. Most of these are manageable with monitoring and dose adjustments, but understanding what to watch for makes a real difference in how safely you can stay on treatment.

How Nintedanib’s Mechanism Explains Its Side Effects

Nintedanib works by blocking several growth-factor receptors at once, including those for vascular endothelial growth factor (VEGF), fibroblast growth factor, and platelet-derived growth factor.¹ That triple blockade is what makes it effective against fibrosis and certain cancers, but those same growth factors have jobs throughout the body. VEGF, for example, helps maintain the lining of blood vessels and the gut. Blocking it explains many of the drug’s downstream problems: disrupted gut lining leads to diarrhea, impaired vessel integrity contributes to bleeding risk, and compromised wound healing becomes a concern around surgery. Understanding this connection helps explain why nintedanib’s side-effect profile looks the way it does, rather than seeming like a random grab bag of unrelated complaints.

Diarrhea Is the Defining Side Effect

In a meta-analysis of randomized controlled trials, about 66% of people taking nintedanib experienced diarrhea, compared with roughly 25% on placebo.² That is a strikingly high rate, and it is the single biggest reason people struggle with the drug. Most cases are mild to moderate, but in one study of 77 patients with idiopathic pulmonary fibrosis, about 35% developed diarrhea severe enough to need medication, and roughly 13% had to stop nintedanib altogether because of it.³

The diarrhea tends to appear early, often within the first few months of treatment. A few factors seem to predict who gets hit hardest. Low body mass index (BMI) has been identified as a significant risk factor, and there is some evidence that concurrent use of prednisolone may reduce the risk.³ A newer study also found that higher levels of a specific autoantibody in the blood were independently associated with early-onset diarrhea after starting nintedanib, which could eventually help clinicians predict who is most vulnerable before treatment begins.⁴

The mechanism behind the diarrhea is not entirely settled, but researchers suspect two pathways: the drug’s receptor blockade disrupts signaling in the gut wall, and nintedanib or its breakdown products may directly inflame the intestinal lining.³ Whatever the exact cause, managing diarrhea early and aggressively with anti-diarrheal agents is the standard approach, and patients are generally advised to have loperamide on hand from day one.

Nausea, Vomiting, Appetite Loss, and Weight Loss

Diarrhea gets the most attention, but it is not the only gastrointestinal problem. Across pooled trial data, about 27% of nintedanib patients reported nausea (versus roughly 11% on placebo), about 16% had vomiting (versus 6%), and about 13% noticed decreased appetite (versus 5%).² Weight loss occurred in about 11% of nintedanib users compared with about 4% on placebo.²

A Dutch survey of patients with idiopathic pulmonary fibrosis confirmed that nintedanib users reported significantly more diarrhea, vomiting, and weight loss compared to people not taking antifibrotic drugs.⁵ Weight loss is worth paying attention to because patients with lung fibrosis often already have reduced nutritional reserves. When diarrhea, nausea, and appetite loss combine, they can push someone into meaningful weight loss that worsens overall health and quality of life. Nutritional counseling alongside treatment is something many clinicians recommend proactively rather than waiting for weight to drop.

Liver Injury

Drug-induced liver injury is the serious side effect that requires the most active monitoring. Nintedanib can cause elevations in liver enzymes, and in a pharmacovigilance analysis, it showed a nearly fivefold higher reporting rate for liver injury compared with pirfenidone, the other main antifibrotic drug. That analysis also found that Asian patients, people with low body weight (around 59 kg on average in cases), and early onset (a median of about two weeks into treatment) were characteristic features of liver injury cases. About a third of affected patients required hospitalization, and over a third had to stop the drug.⁶

A large Taiwanese insurance database study reinforced this concern, finding that nintedanib was associated with roughly 3.6 times the rate of liver injury compared to background rates, after adjusting for age, sex, other medical conditions, and co-prescribed medications.⁷ An FDA adverse-event analysis also found that liver injury was reported more frequently for nintedanib (about 11%) than for pirfenidone (about 6%).⁸

Because liver injury can appear within the first few weeks, liver function tests are standard before starting treatment, then monthly for the first three months, and periodically after that. You should tell your doctor promptly about symptoms like dark urine, unusual fatigue, upper abdominal pain, or yellowing of the skin or eyes. These warrant immediate blood work.

Cardiovascular Events

Because nintedanib blocks VEGF signaling, there has been concern about cardiovascular risk from the beginning. The picture here is more nuanced than with the gut-related side effects. In pooled data from the TOMORROW and INPULSIS trials, among patients who already had elevated cardiovascular risk at baseline, the rate of heart attack was higher in the nintedanib group (about 3.0 per 100 patient-years) compared to placebo (about 1.2 per 100 patient-years). However, the overall rate of major adverse cardiovascular events, which includes heart attack, stroke, and cardiovascular death combined, was similar between nintedanib and placebo in both higher-risk and lower-risk patients.⁹

Post-marketing surveillance data, which track what happens in real-world use over longer periods, have found low absolute rates of cardiovascular events. The rates of heart attack and stroke were each about 3.3 per 1,000 patient-years, and venous blood clots occurred at about 2.0 per 1,000 patient-years.¹⁰ An FDA adverse-event analysis did flag cardiac disorders as a statistically prominent signal for nintedanib, with a reporting odds ratio of about 9.4 compared to other drugs in the database, making it the most striking signal at the system level.⁸ That does not mean most patients experience cardiac problems, but it does mean that anyone with pre-existing heart disease should have a thorough discussion with their prescriber about monitoring.

Bleeding Risk

Nintedanib’s anti-VEGF activity means it can impair the way blood vessels repair themselves, raising a theoretical risk of bleeding. In practice, bleeding events in real-world use have been uncommon. A real-world registry of nearly 2,800 patients with idiopathic pulmonary fibrosis found that bleeding occurred in only about 0.3% overall, though the vast majority of those events were in patients taking nintedanib rather than pirfenidone. Most bleeding episodes were mild or moderate.¹¹ Other real-world reviews have similarly described bleeding as rarely reported.¹²

The main concern is when nintedanib is combined with anticoagulants like warfarin or direct oral anticoagulants. In the registry data, patients taking both nintedanib and anticoagulants had a notably higher incidence of bleeding events than any other group.¹¹ If you are on blood thinners and starting nintedanib, the combination is not automatically ruled out, but it does call for closer surveillance for signs of bleeding, such as unexplained bruising, blood in stool or urine, or prolonged bleeding from cuts.

Gastrointestinal Perforation

This is rare but dangerous. Gastrointestinal perforation, a hole forming in the wall of the stomach or intestine, has been reported at a rate of about 1.0 event per 1,000 patient-years in global pharmacovigilance data.¹³ Other sources cite a rate around 0.2% of patients.¹⁴ The risk is thought to be higher when nintedanib is combined with other VEGF-pathway-targeting drugs, corticosteroids, or nonsteroidal anti-inflammatory drugs, and in patients who have had recent abdominal surgery or have diverticular disease. Symptoms include sudden severe abdominal pain, fever, and nausea. This is a surgical emergency, so any acute belly pain while on nintedanib should be evaluated immediately.

Hypertension

High blood pressure is another class effect of drugs that block VEGF signaling. Phase 4 studies reported hypertension in about 5% of patients on the standard 150 mg dose and about 2% on the 100 mg dose.¹⁵ While those percentages are not alarming, there have been case reports of accelerated or severe hypertension that required urgent intervention. The practical takeaway is that blood pressure should be monitored regularly, especially in the first few months. If you already take blood-pressure medication, your prescriber may want to check whether your current regimen needs adjusting once nintedanib is on board.

How Nintedanib Compares to Pirfenidone

Pirfenidone is the other major antifibrotic drug for idiopathic pulmonary fibrosis, and patients and prescribers frequently compare the two when deciding which to start. Both are similarly effective at slowing lung-function decline, but their side-effect profiles diverge. Nintedanib’s side effects lean heavily gastrointestinal, especially diarrhea, nausea, and vomiting, along with liver injury. Pirfenidone users, by contrast, more often report fatigue, skin-related problems like photosensitivity and rash, and nausea, though weight loss is common with both drugs.¹⁶

A real-world systematic review found that the overall incidence of adverse events was lower with pirfenidone than nintedanib, though discontinuation rates due to side effects were similar between the two drugs and consistent with what trials had shown.¹⁷ In the FDA’s adverse-event reporting system, gastrointestinal disorders were the most frequent category for both drugs, but cardiac disorders stood out as a more prominent signal for nintedanib, and liver injury was reported almost twice as often with nintedanib as with pirfenidone.⁸ None of this means one drug is categorically safer; it means their risks sit in different places, and the choice often comes down to which side-effect profile a particular patient is better equipped to handle.

Dose Adjustments and Keeping Side Effects Manageable

The standard dose is 150 mg twice daily, but when side effects become intolerable, the prescribing information allows a reduction to 100 mg twice daily, temporary treatment interruptions, or both. A reassuring finding from the pivotal INPULSIS trials is that patients who needed these dose modifications saw the same benefit in slowing lung-function decline as patients who tolerated the full dose throughout.¹⁸ That means you do not have to white-knuckle through severe diarrhea or liver enzyme elevations to get the therapeutic benefit. Working with your prescriber to find a tolerable dose is both safe and effective.

In a lung cancer trial assessing patient-reported outcomes, people on nintedanib did report faster onset of gastrointestinal symptoms compared to placebo, but overall quality-of-life scores did not significantly differ between the two groups.¹⁹ This suggests that while the side effects are real and sometimes uncomfortable, for many patients they are manageable enough that they do not drag down overall well-being.

Drug Interactions That Can Change Your Risk

Nintedanib is processed partly through an enzyme system in the liver that can be sped up or slowed down by other medications. In a study with healthy volunteers, co-administration with ketoconazole, a strong enzyme inhibitor used for fungal infections, increased nintedanib exposure by about 60%. Conversely, rifampicin, a strong enzyme inducer used for tuberculosis, cut nintedanib levels roughly in half.²⁰ Higher drug levels can mean worse side effects, particularly diarrhea and liver enzyme elevations; lower levels can mean the drug stops working as well. If you are prescribed a new medication while on nintedanib, it is worth asking your pharmacist or prescriber whether it could interact, especially strong inhibitors or inducers of the CYP3A4 and P-glycoprotein pathways.

Real-World Side Effects Versus Clinical Trials

Clinical trials select patients carefully and monitor them closely, so there has always been a question of whether side effects look different in everyday practice. A systematic review and meta-analysis of real-world studies found that the overall incidence of adverse events with nintedanib was actually lower than what clinical trials reported.¹⁷ Discontinuation rates due to side effects were consistent with trial data, meaning about the same proportion of people eventually stopped the drug because of tolerability issues. No new major adverse events surfaced that had not already been identified in trials. The one concerning finding was that mortality rates were higher in real-world settings than in clinical trials, but this likely reflects the fact that real-world patients tend to be sicker, older, and have more coexisting conditions than trial enrollees.

Kidney Disease, Surgery, and Other Special Situations

Nintedanib has not been studied in people with severe kidney impairment (creatinine clearance below 30 mL/min), and it is listed as contraindicated in those patients because there is simply no safety or pharmacokinetic data available.²¹ For mild to moderate kidney impairment, no dose adjustment is considered necessary based on available data, but close monitoring is still prudent.

Surgery is another area where nintedanib requires planning. Because of its anti-VEGF effects, there is a theoretical risk that wound healing could be impaired. However, a case series of nine patients who continued nintedanib up until lung transplant surgery found no extraordinary bleeding complications and no wound-healing problems afterward.²² That is reassuring, though nine patients is a very small sample. Most clinicians still recommend stopping nintedanib at least a few days before planned surgery and restarting only once adequate wound healing is confirmed. Unplanned or emergency surgery while on the drug warrants careful postoperative monitoring for delayed healing or bleeding.

Nintedanib is also known to cause harm to developing embryos in animal studies, so pregnancy must be ruled out before starting treatment, and effective contraception is essential throughout. The drug’s prescribing label carries a clear warning about embryo-fetal toxicity.