What the label lists and what reports show
Tebentafusp side effects
Tebentafusp's FDA label: “The most common adverse reactions (occurring in ≥ 30%) are cytokine release syndrome, rash, pyrexia, pruritus, fatigue, nausea, chills, abdominal pain, edema, hypotension, dry skin, headache and vomiting ( 6.1 ).” FAERS holds 581 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is cytokine release syndrome (115 reports).
- No generic listed
- Boxed warning
Check it at the source: the tebentafusp FDA label on DailyMed (effective August 20, 2026); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of KIMMTRAK?KIMMTRAK can cause serious side effects, including: See " What is the most important information I should know about KIMMTRAK? ”. Skin reactions. KIMMTRAK may cause skin reactions that require treatment. Tell your healthcare provider if you get symptoms of skin reactions, such as rash, itching, or skin swelling, that are severe and do not go away. Abnormal liver blood tests. Your healthcare provider will do blood tests to check your liver before you start KIMMTRAK and during treatment with KIMMTRAK. Tell your healthcare provider if you get symptoms of liver problems such as right-sided abdominal pain or yellowing of the skin or eyes. […]
Source: FDA drug label, Immunocore Commercial LLC, effective August 20, 2026 (SPL set 24a49f57-d2fc-4ffe-9eb1-fe0460c6b067), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (occurring in ≥ 30%) are cytokine release syndrome, rash, pyrexia, pruritus, fatigue, nausea, chills, abdominal pain, edema, hypotension, dry skin, headache and vomiting ( 6.1 ).
A table the label prints in its adverse reactions section without a title; its column headings name the groups compared
| Reaction | All Grades (%) | Grade 3 or 4 (%) | All Grades (%) | Grade 3 or 4 (% ) |
|---|---|---|---|---|
| Cytokine release syndrome a | 89 | 0.8 | 2.7 | 0 |
| Rash b | 83 | 18 | 28 | 0 |
| Pruritus | 69 | 4.5 | 23 | 0 |
| Dry skin | 31 | 0 | 3.6 | 0 |
| Skin Hypopigmentation b | 28 | NA | 5 | NA |
| Erythema | 24 | 0 | 0.9 | 0 |
| Hair color changes b | 20 | NA | 0 | NA |
| Pyrexia | 76 | 3.7 | 7 | 0.9 |
| Fatigue b | 64 | 6 | 42 | 0.9 |
| Chills | 48 | 0.4 | 3.6 | 0 |
| Edema b | 45 | 0 | 10 | 0 |
| Nausea | 49 | 2 | 26 | 0.9 |
| Abdominal pain b | 45 | 2.9 | 33 | 3.6 |
| Vomiting | 30 | 1.2 | 9 | 0 |
| Diarrhea | 25 | 1.2 | 20 | 2.7 |
| Hypotension | 39 | 3.3 | 2.7 | 0 |
| Headache | 31 | 0.4 | 10 | 0.9 |
| Arthralgia | 22 | 0.8 | 16 | 0 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following serious adverse reactions are discussed in greater detail in other sections of the label: Cytokine Release Syndrome [ see Boxed Warning, Warnings and Precautions (5.1) ] Skin Reactions [ see Warnings and Precautions (5.2) ] Elevated Liver Enzymes [ see Warnings and Precautions (5.3) ] The most common adverse reactions (occurring in ≥ 30%) are cytokine release syndrome, rash, pyrexia, pruritus, fatigue, nausea, chills, abdominal pain, edema, hypotension, dry skin, headache and vomiting ( 6.1 ). The most common laboratory abnormalities (occurring in ≥50%) are decreased lymphocyte count, increased creatinine, increased glucose, increased aspartate aminotransferase, increased alanine aminotransferase, decreased hemoglobin, and decreased phosphate ( 6.1 ). To report SUSPECTED ADVERSE REACTIONS, contact Immunocore at 1-844-IMMUNO1 (1-844-466-8661) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. …
Source: FDA drug label, Immunocore Commercial LLC, effective August 20, 2026 (SPL set 24a49f57-d2fc-4ffe-9eb1-fe0460c6b067), via openFDA; the full label on DailyMed
What do FAERS reports show?
581 reports list tebentafusp among the medicines taken, each a report of something that happened, not proof the medicine caused it; 102 are coded as a death and 195 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 21 reactions below, 14 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Tebentafusp: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions