Medical Oncologist
Tagrisso / Osimertinib
Osimertinib Side Effects: — What to Expect and When
Most people on osimertinib experience some side effects, and most of those are manageable. A few are rare but need urgent review. Knowing the difference — and when to call — is what this page is for.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed August 2026
- Rash is the most common effect — A skin rash or acne-like eruption appears in many patients, usually within the first month.
- Most effects begin early — Diarrhoea, fatigue and dry skin typically appear within the first few weeks.
- Lung effects need same-day action — New breathlessness or cough on osimertinib must be reported the same day — it can be pneumonitis.
- Your team can help manage most of this — Skin care, anti-diarrhoeal guidance and nail care can make a meaningful difference to day-to-day comfort.
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Osimertinib commonly causes a skin rash, diarrhoea, dry skin, and fatigue. Most side effects appear in the first few weeks and are manageable with guidance from your team. A small number of people develop lung inflammation or heart effects that need same-day review. Knowing when to call is what this page covers.
Which side effects do most people experience?
The side effects you are most likely to notice are a skin rash or acne-like eruption, diarrhoea, dry skin, and fatigue. NCCN and ESMO both list these among the most commonly reported effects of osimertinib. Changes around the nails — redness, swelling, or infection of the nail fold — are also common, though they often appear later than the skin and gut effects.
Rash appears mainly on the face and upper body and looks different from ordinary acne — it tends to be redder and more widespread. It is not a sign that the drug is harming you. It is a known skin reaction to drugs that block EGFR.
Diarrhoea is usually manageable. Tell your team if it is more frequent than your usual pattern, lasts more than a day, or does not improve.
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When does each side effect start, and when do you need to call?
| Side effect | How common | Typically starts | Call your team if… |
|---|---|---|---|
| Skin rash / acneiform eruption | Very common | Within the first month | Blistering, raw skin, rapid spread, or severe discomfort |
| Diarrhoea | Very common | First few weeks | Lasting more than 24 hours, any blood, or unable to stay hydrated |
| Dry skin and itching | Very common | First few weeks | Skin cracks or bleeds, or disrupts sleep despite moisturiser |
| Fatigue | Very common | Early on; may persist | Sudden or severe worsening, especially alongside breathlessness |
| Nail changes / paronychia | Common | Often after several weeks to months | Redness, swelling, or pus around the nail — signs of infection |
| Mouth sores (stomatitis) | Common | First few weeks | Unable to eat, drink, or speak comfortably |
| Decreased appetite or nausea | Common | First few weeks | Significant weight loss or unable to eat for more than a day |
| Shortness of breath or new cough | Less common — but serious | Can appear at any time | Report the same day — possible pneumonitis |
| Palpitations or irregular heartbeat | Less common — but serious | Variable | Report the same day |
| Eye irritation or pain | Less common | Variable | Eye pain or any vision change — urgent same-day review |
Does osimertinib affect the heart or lungs?
Lung inflammation — called interstitial lung disease or pneumonitis — is reported in a proportion of patients on osimertinib. It is less common than the skin and gut effects. It is serious, and the key thing that changes the outcome is how quickly it is reported.
Heart effects, including changes in heart rhythm and a reduction in pumping strength, are also reported. Your team may check your heart with an ECG or echocardiogram before and during treatment, particularly if you had a heart condition before starting.
Both effects are monitored as part of your regular care. That is one reason your follow-up appointments matter even when you feel well.
How do I manage specific side effects?
How do I manage the skin rash?
Your oncology team will usually recommend a gentle, fragrance-free moisturiser applied several times a day, a mild soap or soap substitute, and staying out of direct sun. A low-dose antibiotic cream or tablet is sometimes prescribed for more significant rash. Do not use steroid creams without being told to by your team, and avoid harsh skin products. The rash often improves after the first month even if the drug dose stays the same.
What should I do about diarrhoea?
Keep track of how many loose motions you have compared to your usual pattern and let your team know if it is increasing. Small meals, avoiding high-fat or spicy food, and staying well hydrated help. Ask your team before buying anything over the counter — some anti-diarrhoeal medicines can mask worsening symptoms your team needs to see. If you notice blood in your stool or cannot keep fluids down, call the same day.
My nails look different and the skin around them is red. Is that normal?
Paronychia — inflammation and sometimes infection of the skin around the nail — is a known effect of EGFR inhibitors including osimertinib. Keep the area clean and dry, wear gloves for washing up, and avoid cutting the nail too short. If the nail fold becomes painful, swollen, or shows signs of pus, tell your team — a short course of antibiotic treatment usually helps. Do not try to drain it yourself.
Will the fatigue improve, or does it stay?
Fatigue on osimertinib varies between people. Some find it settles after the first few weeks; others find it persists at a lower level throughout treatment. Gentle, regular activity — when you feel able — tends to help more than rest alone; this is what ASCO guidance consistently says for cancer-treatment fatigue. Tell your team if fatigue is stopping you from doing things you want to do. Something correctable, such as anaemia or an underactive thyroid, may be contributing and is worth checking.
Can I take other medicines or supplements alongside osimertinib?
Some over-the-counter medicines are fine alongside osimertinib, and others interact with it or mask a symptom your team needs to know about. Always ask your oncologist or pharmacist before adding anything — including supplements, herbal preparations, and antacids. Certain medicines used for reflux or stomach acid can affect how osimertinib is absorbed, so this question genuinely matters. Your pharmacy team can check for interactions if you bring the packaging in.
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Common questions
Frequently asked questions
When do osimertinib side effects usually start?
Skin rash, diarrhoea and dry skin tend to appear within the first few weeks of starting osimertinib. Nail changes often take longer — sometimes several months in. Lung and heart effects can appear at any time, which is one reason follow-up appointments continue even when you feel well. A new symptom that appears months into treatment can still be drug-related and should be reported to your team.
Do side effects get better the longer I take it?
For many people, skin rash and diarrhoea improve after the first month even without a dose change. Mouth sores often ease as the body adjusts. Fatigue sometimes persists but can be managed with practical changes. Rare but serious effects — lung or heart inflammation — do not resolve on their own and need active treatment. Tell your team about anything that is not improving rather than assuming it will settle.
Does a worse rash mean the drug is working better?
Some research has found a correlation between rash and treatment response in EGFR inhibitors, and your oncologist may mention this. But a more severe rash does not confirm the treatment is working, and a mild rash does not mean it is not. Response is measured by scans and clinical markers, not by how your skin looks. Manage the rash because it affects your comfort and quality of life, not as a performance indicator.
Can osimertinib be taken with food?
Osimertinib can be taken with or without food. Take it at the same time each day for consistency. Certain antacids and medicines used for reflux or stomach acid can reduce the amount of osimertinib your body absorbs — mention anything you take for stomach symptoms to your pharmacist or team. Large amounts of grapefruit products can also affect drug levels and are worth avoiding.
Will side effects be worse if I am also having chemotherapy?
Most people take osimertinib as a single oral tablet rather than in combination with standard chemotherapy. The side effects your team discusses with you are generally those of osimertinib alone. If a combination is planned for your specific situation, your oncologist will explain which effects overlap and how monitoring changes. Do not assume another patient's experience — even someone with the same diagnosis — will match yours.