What Are the Symptoms of Methotrexate-Induced Pneumonitis?

If you are taking methotrexate and develop a persistent dry cough, it is important to take it seriously. While a cough is often caused by a common virus or bacterial pneumonia, it can also be the primary symptom of methotrexate-induced pneumonitis, a rare but serious lung inflammation. This condition is thought to be an immune-mediated or hypersensitivity-like reaction to the drug ^[1].

The most noticeable symptoms include a dry (nonproductive) cough, shortness of breath (dyspnea), feeling generally unwell or fatigued, and fever ^[1][2][3]. A medical evaluation might also reveal abnormally low oxygen levels in your blood (hypoxemia) ^[1].

Distinguishing Pneumonitis from a Cold or Bronchitis

It is completely natural to wonder if your cough is just a common cold. While colds typically involve upper respiratory symptoms like a runny nose, sneezing, and a sore throat, symptom patterns alone cannot reliably distinguish these conditions ^[4][5].

A “chest-only” cough does not automatically mean you have pneumonitis, but methotrexate pneumonitis often causes shortness of breath that worsens even with minimal physical exertion, unlike an uncomplicated cold ^[1][6].

Because methotrexate can suppress your immune system (depending on your dose and other medications you take), you are also more vulnerable to opportunistic infections—infections that take advantage of a weakened immune system. Certain serious lung infections, particularly Pneumocystis jirovecii pneumonia (PCP), can perfectly mimic the exact symptoms of methotrexate pneumonitis ^[4][5].

Because the symptoms overlap so much, methotrexate pneumonitis is considered a “diagnosis of exclusion.” There is no single test that proves you have it. Instead, your doctor must use a combination of tests—such as chest X-rays, CT scans, blood work, and sometimes a bronchoscopy (a procedure performed by a specialist to collect a fluid sample from your airways)—to investigate infections and other causes before confirming the drug is the culprit ^[7][8].

Who is at Risk and When Does It Happen?

This complication most commonly appears during the first year of methotrexate treatment, particularly in the initial weeks or months ^[4][1].

However, you can still develop methotrexate pneumonitis even if you have been taking the medication safely for years or decades ^[7][9]. Your body’s tolerance to the drug in the past does not guarantee you won’t experience this reaction later in life ^[1][7].

Standard Management and When to Seek Care

Methotrexate pneumonitis can progress to severe breathing problems, so early recognition is critical ^[1][9]. However, remember that many other less dangerous conditions can cause a cough. Taking your symptoms seriously does not mean you need to panic.

What You Should Do Now:

• Same-Day Medical Contact: If you develop a new, persistent dry cough, fever, or shortness of breath during normal activity, contact your prescribing doctor for a same-day assessment. Do not take your next dose of methotrexate until you are evaluated ^[10][11].
• Emergency Care: Go to the emergency room or call emergency services if you experience severe or rapidly worsening breathing difficulties, blue or gray lips, confusion, severe chest pain, or an inability to speak in full sentences ^[1][6]. Do not drive yourself to the hospital if you are severely short of breath or faint.
• Using Pulse Oximeters: If you use a home pulse oximeter and your oxygen drops below 90% (or your doctor’s recommended threshold), seek immediate care ^[6]. However, do not delay emergency care to get a reading, and remember that cold fingers, poor circulation, or nail polish can cause inaccurate results.

How It Is Treated:

• Stop the Medication: If your doctor suspects methotrexate pneumonitis, the drug will be discontinued ^[10][11]. It is rarely restarted unless a specialist explicitly recommends it.
• Corticosteroids: Treatment involves taking systemic corticosteroids (prescription anti-inflammatory medications like prednisone) to reduce lung inflammation ^[1][12]. In serious cases, clinicians may start these medications while infection testing is still ongoing.
• Supportive Care: In more severe cases, patients may require hospitalization and supplemental oxygen until their lungs heal ^[12][1].