Medical Oncologist
Enhertu side effects
Trastuzumab Deruxtecan Side Effects: — The Complete List and Timeline
Trastuzumab deruxtecan causes side effects that range from manageable to urgent. Knowing which symptoms are common and expected — and which need a same-day call — is the most useful thing to understand before your first cycle.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Nausea is very common — Most people experience nausea, especially in the days after each infusion. Anti-nausea medicine is given as standard.
- Lung changes are the critical risk — Interstitial lung disease can occur at any point in treatment. Any new breathlessness or cough needs a same-day call.
- Blood counts are monitored every cycle — Low white cells, platelets and red cells are common and are checked before each infusion.
- Hair loss is expected — Most people lose their hair. It typically begins to regrow after treatment ends.
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Trastuzumab deruxtecan causes nausea, fatigue, hair loss, and blood count changes in many patients. The most serious risk is interstitial lung disease — inflammation of the lungs — which can develop at any point during treatment. NCCN and ASCO guidance flags any new breathlessness or dry cough as requiring same-day contact, not a wait-and-see approach.
What side effects does trastuzumab deruxtecan commonly cause?
Trastuzumab deruxtecan delivers chemotherapy directly to cancer cells via an antibody, so it causes both antibody-related and chemotherapy-related side effects.
The most common effects — nausea, fatigue, hair loss, and changes in blood counts — are manageable with support from your team and tend to follow a predictable pattern around each infusion.
Interstitial lung disease is less common but is the most serious risk. This is why your team will ask about your breathing at every visit, and why any new respiratory symptom should be reported the same day rather than saved for your next appointment.
Your heart function is also monitored regularly. The trastuzumab component carries a small risk of reducing how efficiently the heart pumps, and regular echocardiograms allow this to be caught before it causes symptoms.
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Which side effects need a call and when do they typically start?
| Side effect | How common | Typically starts | When to call your team |
|---|---|---|---|
| Nausea and vomiting | Very common — majority of patients | First few days after each infusion | If you cannot keep fluids down for more than a day, or anti-nausea medicine is not helping |
| Fatigue | Very common | Often builds over the first few cycles | If so severe you cannot care for yourself or get out of bed |
| Hair loss | Common | A few weeks after the first infusion | Expected — ask your team about scalp cooling or wig referral before treatment starts |
| Low white blood cells (neutropenia) | Common | Typically mid-cycle; detected on blood tests before each infusion | Immediately if fever or chills develop — go to emergency, do not wait |
| Low platelets (thrombocytopenia) | Common | Mid-cycle pattern, detected on blood tests | If you notice unusual bruising, bleeding gums, or blood in urine or stool |
| Anaemia (low red blood cells) | Common | Can develop gradually across cycles | If very short of breath on minimal activity, or dizzy on standing |
| Interstitial lung disease (ILD) | Occurs in a proportion of patients — NCCN and ASCO flag this as the highest-priority risk | Any point during treatment, including months after starting | Same day — any new cough, breathlessness or chest tightness, however mild |
| Constipation | Common | First week after each infusion | If no bowel movement for several days, or accompanied by pain or vomiting |
| Raised liver enzymes | Occurs in some patients; usually found on blood tests only, rarely symptomatic | Detected on routine monitoring throughout treatment | If skin or eyes appear yellow — call the same day |
| Infusion-related reaction | Less common | During the infusion itself | Alert the nursing team immediately during the infusion — do not wait until after |
What do I need to know about the side effects that worry people most?
Interstitial lung disease — why does everyone keep mentioning it?
Interstitial lung disease (ILD) is inflammation of the fine tissue and air sacs in the lungs. It is caused by the immune response to the drug, not an infection. It carries a black box warning — the most serious level of caution — because it has been severe and has been fatal in a proportion of patients across clinical trials. The reason your team emphasises it is not to frighten you, but because catching it early makes it treatable. The earliest signs are often subtle: a new dry cough, slightly more breathlessness going upstairs, or mild chest tightness. These can seem unrelated to treatment and easy to dismiss. Do not dismiss them. Call the same day. Your team will arrange a chest CT scan. If ILD is confirmed, treatment is paused and corticosteroids are started promptly. Most patients with mild or moderate ILD recover well when it is caught at this stage.
Nausea — how bad is it likely to be and what actually helps?
Nausea on trastuzumab deruxtecan is common enough that anti-nausea medication is given before and after every infusion as standard practice, not as an optional extra. It tends to be worst in the first couple of days after each infusion and usually improves by the end of the first week of the cycle. If your prescribed tablets are not controlling it adequately, say so before your next cycle — there are several options and regimens are adjusted routinely. Between infusions, cold foods, small frequent meals, and ginger drinks help some people. Avoid very spicy or greasy food in the days after each infusion. If you cannot keep fluids down for more than a day, call your team that day rather than waiting to see if it settles.
Blood count monitoring — what happens if my counts are too low?
Your blood is tested before every infusion. The three numbers your team watches are white blood cells, which fight infection; platelets, which stop bleeding; and haemoglobin, which carries oxygen. If white cells are too low, your next infusion may be delayed by a week to allow recovery. Growth factor injections are sometimes prescribed to support the counts between cycles. During the period of lowest counts — typically mid-cycle — your infection risk is highest. A fever during this window is a medical emergency. Take your temperature if you feel unwell and go straight to the emergency department, telling them you are on cancer treatment. Do not wait until morning, and do not wait for a callback.
Hair loss — will it definitely happen and does it grow back?
Hair loss on trastuzumab deruxtecan is common. Because the drug contains a chemotherapy payload, it affects hair more than most targeted therapies do. Hair typically begins to thin or shed a few weeks after the first infusion, and most people lose most or all of their scalp hair. Scalp cooling (cold cap therapy) reduces hair loss in some patients and is offered at some centres — ask your team about it before your first infusion, because it must be arranged in advance. It does not work for everyone, and your team will be honest about whether it is likely to help in your situation. Hair almost always grows back after treatment ends, though the regrowth sometimes has a different texture or curl at first. This usually normalises over time.
Heart monitoring — why is an echocardiogram part of the schedule?
Trastuzumab deruxtecan contains trastuzumab, which in a small proportion of patients reduces the heart's pumping efficiency — a measure called left ventricular ejection fraction. This is the same reason that standard trastuzumab (Herceptin) requires regular heart scans. Your team will schedule echocardiograms at set intervals throughout your treatment. Between scans, report any ankle swelling, unusual shortness of breath when lying flat, or palpitations. Most changes detected on monitoring are mild and reversible with a treatment pause. The monitoring exists specifically to catch changes before they become symptomatic — which is why keeping your echo appointments matters as much as attending your infusions.
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Common questions
Frequently asked questions
Is interstitial lung disease likely to happen to me?
ILD occurs in a proportion of patients, not in all of them, and many people complete treatment without developing it. The risk is real enough to carry a black box warning and to require active monitoring throughout treatment. The most important thing you can do is report any new cough or change in breathing the same day it appears, rather than assuming it is coincidence. Catching ILD at an early, mild stage is what makes it treatable — and that depends entirely on how quickly it is reported.
Can I take anti-nausea medicines from the pharmacy alongside what my team prescribes?
Ask your team before adding anything, including over-the-counter medicines. Some common anti-nausea tablets interact with the medications already prescribed, and some affect the heart's electrical rhythm in ways that matter more on cancer treatment. If your prescribed medicines are not working well enough, tell your team — that is important feedback and regimens are adjusted routinely. Self-managing silently is less safe than asking.
How will I know when my infection risk is highest in the cycle?
Your oncology team will tell you the window in your cycle when blood counts typically reach their lowest. Note that window in your phone or a diary. During that period, take your temperature if you feel unwell, even mildly. Some teams provide a written fever plan and a thermometer before discharge after your first infusion. If yours has not done so, ask before you leave clinic — you want that plan before you need it, not while you are already unwell.
Will I need to stop treatment if I get a side effect?
Not necessarily. Many side effects are managed by adjusting doses, delaying the next infusion, or adding supportive medicines — not by stopping treatment altogether. Severe side effects such as significant ILD or major cardiac changes may require treatment to be paused or ended, and that decision is weighed against how well the treatment is working for you. Reporting side effects promptly — rather than tolerating them in silence — is what keeps the milder management options available.
What should I tell a doctor who is not my oncologist?
Tell any doctor you see that you are on trastuzumab deruxtecan and show them your treatment information. This matters if you need a new medicine — including an antibiotic — because some drugs interact with T-DXd or affect the same cardiac and liver parameters your team monitors. Carry your oncology contact number with you and ask any other prescribing doctor to check new medicines with your oncology team before you start them.