Drug-Induced Pulmonary Fibrosis: Medications That Scar the Lungs

Most people assume that if a doctor prescribes a medication, it’s safe. But some drugs don’t just treat illness-they can quietly scar your lungs. Drug-induced pulmonary fibrosis is one of the most dangerous, yet underrecognized, side effects of common prescriptions. It doesn’t come with warning signs you can easily spot. No rash. No nausea. Just a dry cough that won’t go away, and breathlessness that gets worse every week. By the time it’s diagnosed, the damage is often permanent.

What Exactly Is Drug-Induced Pulmonary Fibrosis?

Pulmonary fibrosis means scar tissue builds up in your lungs. Normally, the tiny air sacs (alveoli) stretch and relax to move oxygen into your blood. When scar tissue replaces healthy tissue, those sacs stiffen. Breathing becomes like trying to suck air through a clogged straw. Drug-induced pulmonary fibrosis happens when certain medications trigger this scarring process. It’s not an allergic reaction. It’s not an overdose. It’s unpredictable-some people get it after a few months, others after years, and most never do at all.

The exact reason why only some people develop it remains unknown. Researchers think it has to do with how your body metabolizes the drug, your genetics, and your age. Older adults are at higher risk. So are people with pre-existing lung conditions. But even healthy 60-year-olds on routine medications can develop it. The key is that this isn’t rare. Between 2014 and late 2024, New Zealand’s pharmacovigilance system recorded 173 cases linked to medications-with 30 deaths. That’s a 17% fatality rate. And those are just the reported cases. Many more go undiagnosed.

The Top Medications That Cause Lung Scarring

Over 50 drugs have been linked to pulmonary fibrosis. But a handful account for the vast majority of cases. Here are the most dangerous ones, backed by real-world data:

• Nitrofurantoin-Used for urinary tract infections, especially in older women on long-term prevention. Over 47 cases were reported in New Zealand between 2014 and 2024. Symptoms can appear after 6 months or even 10 years. It’s often mistaken for pneumonia or aging.
• Methotrexate-A common treatment for rheumatoid arthritis and psoriasis. About 3-7% of users develop lung inflammation that turns into fibrosis. In New Zealand, 45 cases were reported in 10 years. It can strike suddenly-sometimes within weeks-with fever, cough, and rapid breathing.
• Amiodarone-Prescribed for irregular heart rhythms. About 5-7% of long-term users develop lung damage. Risk rises after taking more than 400 grams total. It’s slow to show up-usually after 6 to 12 months. But once it does, it’s hard to reverse.
• Bleomycin-A chemotherapy drug. Up to 20% of patients on high doses develop severe lung scarring. It’s one of the most toxic in this category. Doctors know the risk, but it’s still used because it’s effective against certain cancers.
• Cyclophosphamide-Another chemo drug. Around 3-5% of users get lung injury. It’s often combined with other drugs, making it harder to pinpoint.
• Immune checkpoint inhibitors-Newer cancer drugs like pembrolizumab and nivolumab. Since their approval in 2011, reports of lung fibrosis have jumped. The immune system, unleashed to fight cancer, sometimes attacks the lungs instead.

What’s scary is that these drugs aren’t obscure. Nitrofurantoin is one of the most prescribed antibiotics for UTIs. Methotrexate is a go-to for arthritis. Amiodarone is used in millions of heart patients. If you’re on any of these, you’re not a statistical outlier-you’re a regular patient.

How Do You Know If It’s Your Medication?

The symptoms are easy to ignore. A dry cough. Feeling winded climbing stairs. Tired all the time. Many patients assume it’s just getting older. Or they blame their asthma, their weight, or a cold that won’t quit. But if you’ve been on one of these drugs for more than a few months and you’re noticing these changes, don’t brush it off.

According to patient reports from pulmonary fibrosis support groups, the average time from first symptom to correct diagnosis is 8.2 weeks. That’s two months of lung damage happening while doctors look elsewhere. The key clues:

• Cough that doesn’t respond to cough medicine
• Shortness of breath during normal activities (walking, showering, dressing)
• Crackling sound in lungs when a doctor listens with a stethoscope
• Low oxygen levels during a simple walk test
• Scarring visible on a high-resolution CT scan of the chest

There’s no single test that says, “This drug caused this.” Diagnosis is a process of elimination. Your doctor must rule out infections, autoimmune diseases, asbestos exposure, and other lung conditions. That’s why your medication history matters more than you think. Bring a full list-prescriptions, supplements, even over-the-counter drugs. Don’t assume your doctor knows what you’re taking. Many don’t ask.

What Happens If You Keep Taking the Drug?

Continuing the medication means more scarring. And scarring is permanent. Once collagen builds up in the lungs, it doesn’t go away. Stopping the drug early is the only way to stop progression. In fact, 89% of patients who stop the offending drug within 3 months see improvement. Their lungs heal, their breathing gets better, their oxygen levels rise.

But if you wait too long? The damage becomes irreversible. About 15-25% of patients end up with permanent lung function loss-even after stopping the drug. And in severe cases, mortality hits 10-20%. Amiodarone-induced fibrosis, for example, kills 1 in 5 patients even after treatment stops.

That’s why timing is everything. The earlier you catch it, the better your chances. Waiting for a CT scan or a referral to a lung specialist isn’t just inconvenient-it’s dangerous.

How Is It Treated?

There’s no cure for the scarring itself. But you can stop it from getting worse-and sometimes reverse some of the damage.

The first step is always stopping the drug. That’s non-negotiable. The second step? High-dose steroids. Prednisone, usually 0.5 to 1 mg per kilogram of body weight daily, for 3-6 months. It reduces inflammation and slows further scarring. Many patients feel better within weeks.

Oxygen therapy is used if your blood oxygen drops below 88%. It doesn’t fix the lungs, but it keeps you alive and active while your body heals. Pulmonary rehab-breathing exercises, light exercise training, education-helps most patients regain strength and confidence.

But here’s the hard truth: if the fibrosis is advanced, steroids won’t help much. That’s why prevention and early detection are the only real wins.

Who’s at Risk-and What Should You Do?

You’re at higher risk if you:

• Are over 60
• Take nitrofurantoin, methotrexate, or amiodarone long-term
• Have a history of lung disease or smoking
• Are on multiple medications (drug interactions increase risk)

Here’s what to do now:

1. If you’re on any of the high-risk drugs listed above, ask your doctor: “Could this be affecting my lungs?”
2. Get a baseline pulmonary function test (PFT) before starting long-term therapy.
3. Keep a symptom journal: note when you feel winded, when you cough, if you feel feverish.
4. If you develop a new cough or breathlessness, don’t wait. Go to your doctor and say: “I’m on [drug name]. Could this be lung damage?”
5. Ask for a chest CT scan if symptoms persist. It’s the only way to see early scarring.

Primary care doctors miss this diagnosis more than you think. A 2022 survey found only 58% routinely screen for lung symptoms in patients on high-risk drugs. That means nearly half of patients are flying blind. Don’t be one of them.

The Bigger Picture

Drug-induced pulmonary fibrosis is rising. Reported cases have gone up 23.7% over the past decade. Why? More people are on long-term medications. More new drugs are hitting the market-especially cancer immunotherapies-with unknown lung risks. And our systems aren’t keeping up.

Regulators in New Zealand, the U.S., and Europe are now pushing for better warnings. Some hospitals are starting to recommend baseline lung tests before prescribing amiodarone or methotrexate. But it’s still not standard. You have to ask.

This isn’t just about one drug. It’s about trusting your body. If something feels off, it probably is. If your breath isn’t what it used to be, don’t assume it’s age. Don’t assume it’s nothing. Your lungs can’t tell you they’re being damaged. You have to be their advocate.

What Comes Next?

The future of preventing drug-induced pulmonary fibrosis lies in better screening and personalized medicine. Researchers are looking for genetic markers that predict who’s at risk before they even start a drug. Clinical trials are testing blood tests that detect early lung injury-before symptoms appear.

Until then, your best defense is awareness. Know the drugs that can harm your lungs. Track your symptoms. Speak up. Your lungs don’t scream-they whisper. And if you don’t listen, the damage will keep building, silently, until it’s too late.