What the label lists and what reports show

Cemiplimab side effects

Cemiplimab's FDA label: “Most common adverse reactions (≥15%): LIBTAYO as a single agent in mCSCC or laCSCC, m BCC or laBCC, and NSCLC with high PD-L1 expression: Fatigue, musculoskeletal pain, rash, diarrhea, and anemia.” FAERS holds 2,008 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 fatigue (87 reports).

No generic listed

Check it at the source: the cemiplimab FDA label on DailyMed (effective August 31, 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 LIBTAYO?
LIBTAYO can cause serious side effects. See " What is the most important information I should know about LIBTAYO? " The most common side effects of LIBTAYO when used alone to treat CSCC that has spread or cannot be cured by surgery or radiation, BCC or NSCLC include: tiredness muscle or bone pain rash diarrhea low levels of red blood cells (anemia) The most common side effects of LIBTAYO when used alone to help prevent CSCC from coming back include: rash itching The most common side effects of LIBTAYO when used in combination with platinum-containing chemotherapy to treat NSCLC include: hair loss muscle or bone pain nausea tiredness numbness, pain, tingling or burning in your hands or feet decreased appetite These are not all the possible side effects of LIBTAYO. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Source: FDA drug label, Regeneron Pharmaceuticals, Inc., effective August 31, 2026 (SPL set 4347ae1f-d397-4f18-8b70-03897e1c054a), via openFDA; the full label on DailyMed

What does the label list?

From the label: adverse reactions
Most common adverse reactions (≥15%): LIBTAYO as a single agent in mCSCC or laCSCC, m BCC or laBCC, and NSCLC with high PD-L1 expression: Fatigue, musculoskeletal pain, rash, diarrhea, and anemia.

Table 7: Adverse Reactions in ≥10% of Patients with Advanced BCC Receiving LIBTAYO in Study 1620

Reaction	Adverse Reactions All Grades %	LIBTAYO N = 138 Grades 3-4 %
Fatigue Fatigue is a composite term that includes fatigue, asthenia, and malaise	50	4.3
Edema Edema is a composite term that includes peripheral edema, peripheral swelling, and…	10	0.7
Musculoskeletal pain Musculoskeletal pain is a composite term that includes arthralgia,…	36	2.9
Diarrhea Diarrhea is a composite term that includes diarrhea, colitis, autoimmune…	33	4.3
Nausea	13	0.7
Abdominal pain Abdominal pain is a composite term that includes abdominal pain, abdominal…	12	1.4
Constipation	12	0.7
Rash Rash is a composite term that includes rash maculo-papular, eczema, rash,…	30	0.7
Pruritus	19	0
Upper respiratory tract infection Upper respiratory tract infection is a composite term…	22	0
Urinary tract infection Urinary tract infection is a composite term that includes urinary…	13	2.2
Hemorrhage Hemorrhage is a composite term that includes tumor hemorrhage, hematuria,…	18	0.7
Hypertension Hypertension is a composite term that includes hypertension, blood pressure…	17	9
Decreased appetite	14	1.4
Anemia	14	0.7
Dyspnea Dyspnea is a composite term that includes dyspnea and dyspnea exertional	14	0
Acute kidney injury Acute kidney injury is a composite term that includes blood…	14	0
Headache	13	1.4
Dizziness Dizziness is a composite term that includes dizziness and vertigo	12	0
Peripheral neuropathy Peripheral neuropathy is a composite term that includes…	11	0
Hypothyroidism Hypothyroidism is a composite term that includes hypothyroidism, blood…	12	0
Liver function test abnormalities Liver function test abnormalities is a composite term…	10	1.4

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, continued
The following serious adverse reactions are described elsewhere in the labeling. Severe and Fatal Immune-Mediated Adverse Reactions [see Warnings and Precautions (5.1) ] Infusion-Related Reactions [see Warnings and Precautions (5.2) ] Complications of Allogeneic HSCT [see Warnings and Precautions (5.3) ] Most common adverse reactions (≥15%): LIBTAYO as a single agent in mCSCC or laCSCC, m BCC or laBCC, and NSCLC with high PD-L1 expression: Fatigue, musculoskeletal pain, rash, diarrhea, and anemia. ( 6.1 ) LIBTAYO as a single agent in adjuvant CSCC at high risk of recurrence: Rash and pruritus. ( 6.1 ) LIBTAYO in combination with platinum-based chemotherapy in NSCLC: Alopecia, musculoskeletal pain, nausea, fatigue, peripheral neuropathy, and decreased appetite. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Regeneron at 1-877-542-8296 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, Regeneron Pharmaceuticals, Inc., effective August 31, 2026 (SPL set 4347ae1f-d397-4f18-8b70-03897e1c054a), via openFDA; the full label on DailyMed

What do FAERS reports show?

2,008 reports list cemiplimab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 418 are coded as a death and 571 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 20 reactions below, 17 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

Death (an outcome recorded in the report)166
Disease Progression (a use or a product term, not a reaction)152
Off Label Use (a use or a product term, not a reaction)105
Fatigue (named in the label)87
Rash (named in the label)86
Dyspnoea (named in the label)63
Pyrexia (named in the label)61
Pruritus (named in the label)51
Myocarditis (named in the label)49
Drug Ineffective (a use or a product term, not a reaction)47
Asthenia (named in the label)46
Interstitial Lung Disease46
Nausea (named in the label)45
Diarrhoea (named in the label)44
Pneumonia (named in the label)40
Condition Aggravated (a use or a product term, not a reaction)37
Hypothyroidism (named in the label)36
Pneumonitis (named in the label)35
Vomiting (named in the label)32
General Physical Health Deterioration31
Infusion Related Reaction (named in the label)31
Acute Kidney Injury (named in the label)30
Colitis (named in the label)30
Myositis (named in the label)30
Sepsis30

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Cemiplimab: 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