Temozolomide side effects: what 20,948 FDA adverse event reports show

Temozolomide · 1,047 reaction terms · 64,154 drug–reaction co-reports · data 2026-09-14

Drug class

Alkylating Drug

FDA label (Established Pharmacologic Class) · compare the class

Who reports

20,948 reports · 81% serious · 4,436 with death outcome · 46% female

openFDA FAERS counts, all years, deduplication not applied

Used for

1. INDICATIONS AND USAGE TEMOZOLOMIDE Capsules are an alkylating drug indicated for the treatment of adult patients with: Newly diagnosed glioblastoma concomitantly with radiotherapy and then as maintenance treatment. ( 1.1 ) Anaplastic astrocytoma ( 1.2 ) Adjuvant treatment of adults with newly diagnosed anaplastic astrocytoma. ( 1.2 ) Treatment of adults with refractory anaplastic astrocytoma.

FDA label, Indications and Usage

What it is

11. DESCRIPTION Temozolomide is an alkylating drug.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 40 strongest signals

Labeled adverse reaction 1Labeled (related wording) 4Likely indication confounding 4Reporting / coding artifact 1Not in label — unassessed 30

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 1,007 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Hypermutation	132	32,563.2 12,043.7–88,043.4ROR 32,769.7 · χ² 125,458 / p <1e-300	840.9 EB05 727.2 · IC025 +7.4 3/3 methods agree	Not in label — unassessed	serious n=48 · 100% clinician	not reported in cached trials
Malignant cranial nerve neoplasm	17	1,863.9 830.9–4,180.9ROR 1,865.4 · χ² 10,321 / p <1e-300	373.6 EB05 247.1 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=17	not reported in cached trials
Desmoplastic small round cell tumour	47	1,159.4 760.7–1,767.1ROR 1,162.1 · χ² 24,481 / p <1e-300	438.1 EB05 342.7 · IC025 +5.9 3/3 methods agree	Not in label — unassessed	serious n=46 · ♀ 67% (drug 46%) · 98% clinician	not reported in cached trials
Dna mismatch repair protein gene mutation	11	904.5 399.2–2,049.7ROR 905.0 · χ² 4,719 / p <1e-300	259.6 EB05 154.7 · IC025 +3.4 3/3 methods agree	Not in label — unassessed	serious n=7	not reported in cached trials
Retro-orbital neoplasm	17	466.0 261.8–829.4ROR 466.4 · χ² 5,046 / p <1e-300	233.8 EB05 154.6 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=17	not reported in cached trials
Gliosarcoma	10	411.2 196.6–859.7ROR 411.3 · χ² 2,606 / p <1e-300	187.3 EB05 108.7 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious n=10	not reported in cached trials
Brain stem glioma	35	303.0 207.5–442.3ROR 303.5 · χ² 7,830 / p <1e-300	206.0 EB05 154.9 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious n=35 · ♀ 68% (drug 46%) · 97% clinician	not reported in cached trials
Anaplastic astrocytoma	35	265.7 183.0–385.8ROR 266.1 · χ² 7,064 / p <1e-300	188.1 EB05 141.4 · IC025 +5.2 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious n=35	not reported in cached trials
Medulloblastoma recurrent	23	252.2 159.6–398.6ROR 252.4 · χ² 4,385 / p <1e-300	172.5 EB05 121.1 · IC025 +4.6 3/3 methods agree	Not in label — unassessed	serious n=23 · 100% clinician	not reported in cached trials
Neuroblastoma recurrent	38	232.9 163.6–331.6ROR 233.3 · χ² 6,912 / p <1e-300	172.4 EB05 131.1 · IC025 +5.2 3/3 methods agree	Not in label — unassessed	serious n=37 · ♀ 18% (drug 46%)	not reported in cached trials
Glioblastoma multiforme	158	229.6 193.2–272.9ROR 231.4 · χ² 28,991 / p <1e-300	182.4 EB05 159.7 · IC025 +6.6 3/3 methods agree	Labeled (related wording) related wording	serious n=157	not reported in cached trials
Astrocytoma	71	221.7 171.5–286.7ROR 222.5 · χ² 12,558 / p <1e-300	172.9 EB05 141.7 · IC025 +5.9 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious n=71 · ♀ 22% (drug 46%) · 91% clinician	not reported in cached trials
Tumour pseudoprogression	186	207.2 177.0–242.5ROR 209.0 · χ² 31,370 / p <1e-300	168.4 EB05 149.1 · IC025 +6.6 3/3 methods agree	Not in label — unassessed	serious n=185 · 97% clinician	not reported in cached trials
Ganglioneuroma	11	201.0 105.1–384.4ROR 201.1 · χ² 1,656 / p <1e-300	130.0 EB05 77.5 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious n=11	not reported in cached trials
Malignant glioma	24	200.7 129.4–311.2ROR 200.9 · χ² 3,799 / p <1e-300	147.6 EB05 104.4 · IC025 +4.6 3/3 methods agree	Not in label — unassessed	serious n=24 · 100% clinician	not reported in cached trials
Glioblastoma	269	192.1 168.7–218.7ROR 194.6 · χ² 42,643 / p <1e-300	159.1 EB05 143.8 · IC025 +6.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious n=262	not reported in cached trials
Autologous haematopoietic stem cell transplant	14	189.2 106.8–335.2ROR 189.4 · χ² 2,044 / p <1e-300	131.0 EB05 82.9 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious n=14	not reported in cached trials
Oligodendroglioma	17	162.9 97.5–272.0ROR 163.0 · χ² 2,210 / p <1e-300	121.2 EB05 80.2 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious n=17	not reported in cached trials
Radiation necrosis	67	133.6 103.5–172.3ROR 134.0 · χ² 7,648 / p <1e-300	114.0 EB05 92.9 · IC025 +5.6 3/3 methods agree	Not in label — unassessed	serious n=62 · 94% clinician	NCT00943826: 1/450 (0.2%) control (serious AE)
Angina bullosa haemorrhagica	27	130.0 87.0–194.1ROR 130.1 · χ² 2,940 / p <1e-300	106.5 EB05 76.9 · IC025 +4.6 3/3 methods agree	Not in label — unassessed	serious n=27 · 96% clinician	not reported in cached trials
Parathyroid tumour malignant	14	121.2 69.6–211.1ROR 121.3 · χ² 1,381 / p <1e-300	94.5 EB05 59.8 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious n=14	not reported in cached trials
Astrocytoma malignant	10	116.1 60.3–223.5ROR 116.1 · χ² 920 / p 2e-202	87.2 EB05 50.6 · IC025 +3.1 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=10	not reported in cached trials
Pancreatic neuroendocrine tumour metastatic	24	111.7 73.3–170.3ROR 111.8 · χ² 2,267 / p <1e-300	93.2 EB05 65.9 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious n=24 · ♀ 0% (drug 46%)	not reported in cached trials
Ependymoma	13	97.9 55.4–173.1ROR 98.0 · χ² 1,048 / p 3e-230	79.2 EB05 49.2 · IC025 +3.4 3/3 methods agree	Not in label — unassessed	serious n=13	not reported in cached trials
Glioma	55	93.9 71.2–123.8ROR 94.1 · χ² 4,531 / p <1e-300	83.4 EB05 66.5 · IC025 +5.2 3/3 methods agree	Labeled adverse reaction exact term	serious n=54 · 98% clinician	not reported in cached trials
Herpes simplex encephalitis	38	91.9 65.9–128.1ROR 92.1 · χ² 3,043 / p <1e-300	80.9 EB05 61.5 · IC025 +4.8 3/3 methods agree	Not in label — unassessed	serious n=38 · 92% clinician	not reported in cached trials
Brain tumour operation	17	91.7 55.8–150.6ROR 91.7 · χ² 1,313 / p 8e-288	77.0 EB05 50.9 · IC025 +3.8 3/3 methods agree	Reporting / coding artifact	serious n=17	not reported in cached trials
Neuroblastoma	30	86.3 59.4–125.3ROR 86.4 · χ² 2,248 / p <1e-300	75.8 EB05 55.6 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=29 · 100% clinician	not reported in cached trials
Vasogenic cerebral oedema	49	74.5 55.7–99.6ROR 74.7 · χ² 3,236 / p <1e-300	67.6 EB05 53.1 · IC025 +4.9 3/3 methods agree	Not in label — unassessed	serious n=48 · ♀ 76% (drug 46%) · 96% clinician	not reported in cached trials
Central nervous system necrosis	19	73.8 46.3–117.6ROR 73.9 · χ² 1,203 / p 7e-264	64.5 EB05 43.6 · IC025 +3.9 3/3 methods agree	Labeled (related wording) related wording	serious n=19	not reported in cached trials
Astrocytoma, low grade	10	61.7 32.6–116.8ROR 61.7 · χ² 506 / p 2e-112	52.6 EB05 30.5 · IC025 +2.9 3/3 methods agree	Labeled (related wording) related wording	serious n=10	not reported in cached trials
Intracranial tumour haemorrhage	22	60.8 39.5–93.5ROR 60.9 · χ² 1,163 / p 3e-255	54.8 EB05 38.1 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	serious n=22	NCT00943826: 1/461 (0.2%) on Temozolomide (serious AE)
Vanishing bile duct syndrome	57	54.1 41.5–70.7ROR 54.3 · χ² 2,768 / p <1e-300	50.6 EB05 40.5 · IC025 +4.7 3/3 methods agree	Not in label — unassessed	serious n=56 · ♀ 10% (drug 46%) · 100% clinician	not reported in cached trials
Aspergillus infection	327	53.1 47.6–59.3ROR 54.0 · χ² 15,827 / p <1e-300	50.3 EB05 45.9 · IC025 +5.4 3/3 methods agree	Not in label — unassessed	serious n=327	not reported in cached trials
Tumour necrosis	47	46.8 35.0–62.8ROR 46.9 · χ² 1,970 / p <1e-300	44.0 EB05 34.4 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=47	not reported in cached trials
Pneumocystis jiroveci infection	12	44.5 25.0–79.4ROR 44.5 · χ² 448 / p 1e-99	40.1 EB05 24.5 · IC025 +3.0 3/3 methods agree	Labeled (related wording) related wording	serious n=11	not reported in cached trials
Vulval disorder	27	42.4 28.9–62.3ROR 42.5 · χ² 1,008 / p 2e-221	39.7 EB05 28.6 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious n=27 · 93% clinician	not reported in cached trials
Eastern cooperative oncology group performance status worsened	49	41.0 30.9–54.6ROR 41.1 · χ² 1,800 / p <1e-300	38.9 EB05 30.6 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious n=49 · 98% clinician	not reported in cached trials
Craniotomy	16	40.6 24.6–66.9ROR 40.6 · χ² 556 / p 3e-123	37.4 EB05 24.4 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious n=12	not reported in cached trials
Pancreatic neuroendocrine tumour	23	37.2 24.5–56.4ROR 37.2 · χ² 746 / p 1e-164	34.9 EB05 24.5 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious n=23 · ♀ 0% (drug 46%)	not reported in cached trials

Trial evidence (ClinicalTrials.gov)

✓ Trial adverse-event data found on ClinicalTrials.gov

Largest completed trials with posted results that list Temozolomide as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (2 of 40 signal terms matched).

NCT00304031 — Radiation Therapy (RT) and Temozolomide (TMZ) in Treating Patients With Newly Diagnosed Glioblastoma or Gliosa (N=1173, PHASE3; 263 AE terms posted; arms: No Adjuvant TMZ (Not Randomized); Conventional Adjuvant TMZ; Dose-dense Adjuvant TMZ)
NCT00943826 — A Study of Bevacizumab (Avastin®) in Combination With Temozolomide and Radiotherapy in Participants With Newly (N=921, PHASE3; 247 AE terms posted; arms: Bevacizumab + RT+Temozolomide; Placebo + RT+Temozolomide)

Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Disease progression	1,886	16.3 15.6–17.0ROR 17.8 · χ² 26,699 / p <1e-300	16.0 EB05 15.4 · IC025 +3.9 3/3 methods agree	Reporting / coding artifact	serious PRR 11.9	NCT00304031: 6/285 (2.1%) on Temozolomide (serious AE)
Off label use (used outside approved label)	1,801	2.1 2.0–2.2ROR 2.2 · χ² 1,050 / p 2e-230	2.1 EB05 2.0 · IC025 +1.0	Reporting / coding artifact	serious PRR 1.9 · 90% clinician	not reported in cached trials
Death	1,771	2.1 2.0–2.2ROR 2.2 · χ² 1,005 / p 8e-221	2.1 EB05 2.0 · IC025 +1.0	Outcome field, not a reaction	serious PRR 1.4	NCT00304031: 2/285 (0.7%) on Temozolomide (serious AE)
Thrombocytopenia (low platelets)	1,572	14.3 13.6–15.0ROR 15.4 · χ² 19,259 / p <1e-300	14.1 EB05 13.5 · IC025 +3.7 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 9.9	NCT00943826: 17/461 (3.7%) on Temozolomide; 8/450 (1.8%) control (serious AE)
Product use in unapproved indication	1,445	6.0 5.7–6.3ROR 6.3 · χ² 5,980 / p <1e-300	5.9 EB05 5.7 · IC025 +2.5 3/3 methods agree	Reporting / coding artifact	serious PRR 3.2 · 95% clinician	not reported in cached trials
Nausea	1,308	1.7 1.6–1.8ROR 1.7 · χ² 356 / p 1e-79	1.7 EB05 1.6 · IC025 +0.6	Labeled adverse reaction exact term	serious PRR 1.8	NCT00304031: 6/285 (2.1%) on Temozolomide (serious AE)
Drug ineffective (drug did not work)	1,263	1.0 0.9–1.0ROR 1.0 · χ² 2 / p 0.070	1.0 EB05 0.9 · IC025 -0.2 PRR-only: not supported by EBGM or IC	Reporting / coding artifact	serious PRR 1.6 · 93% clinician	not reported in cached trials
Fatigue (tiredness)	1,037	1.3 1.3–1.4ROR 1.4 · χ² 91 / p 8e-22	1.3 EB05 1.3 · IC025 +0.3	Labeled adverse reaction exact term	serious PRR 1.4	NCT00304031: 9/285 (3.2%) on Temozolomide (serious AE)
Neutropenia (low neutrophils (infection-fighting cells))	1,035	7.7 7.3–8.2ROR 8.0 · χ² 6,018 / p <1e-300	7.6 EB05 7.2 · IC025 +2.8 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 5.5	NCT00304031: 2/285 (0.7%) on Temozolomide (serious AE)
Vomiting	977	2.1 2.0–2.2ROR 2.1 · χ² 564 / p 5e-125	2.1 EB05 2.0 · IC025 +1.0	Labeled adverse reaction exact term	serious PRR 1.9	NCT00304031: 5/285 (1.8%) on Temozolomide (serious AE)
Malignant neoplasm progression	930	9.2 8.7–9.8ROR 9.6 · χ² 6,772 / p <1e-300	9.1 EB05 8.6 · IC025 +3.1 3/3 methods agree	Reporting / coding artifact	serious PRR 6.5	not reported in cached trials
Febrile neutropenia	827	12.6 11.8–13.5ROR 13.1 · χ² 8,775 / p <1e-300	12.5 EB05 11.8 · IC025 +3.5 3/3 methods agree	Labeled (related wording) related wording	serious PRR 8.9	NCT00304031: 2/285 (0.7%) on Temozolomide (serious AE)
Diarrhoea (diarrhea)	785	1.2 1.1–1.3ROR 1.2 · χ² 32 / p 6e-9	1.2 EB05 1.2 · IC025 +0.2	Labeled adverse reaction exact term	serious PRR 1.4	NCT00304031: 1/285 (0.4%) on Temozolomide (serious AE)
Anaemia (low red blood cells)	759	4.0 3.7–4.3ROR 4.1 · χ² 1,708 / p <1e-300	4.0 EB05 3.7 · IC025 +1.9 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.0	NCT00943826: 3/461 (0.7%) on Temozolomide (serious AE)
Asthenia (weakness)	643	1.7 1.6–1.8ROR 1.7 · χ² 193 / p 3e-44	1.7 EB05 1.6 · IC025 +0.6	Labeled adverse reaction exact term	serious PRR 1.6	NCT00943826: 86/461 (18.7%) on Temozolomide; 63/450 (14.0%) control

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Hypermutation — n=132, PRR 32,563.2
Desmoplastic small round cell tumour — n=47, PRR 1,159.4
Brain stem glioma — n=35, PRR 303.0
Medulloblastoma recurrent — n=23, PRR 252.2
Neuroblastoma recurrent — n=38, PRR 232.9
Tumour pseudoprogression — n=186, PRR 207.2
Malignant glioma — n=24, PRR 200.7
Radiation necrosis — n=67, PRR 133.6 (also seen in trial arm)
Angina bullosa haemorrhagica — n=27, PRR 130.0
Pancreatic neuroendocrine tumour metastatic — n=24, PRR 111.7

✓ A hand-written Bradford Hill causality assessment exists for this drug: Temozolomide ↔ Thrombocytopenia.

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Temozolomide?

In FDA FAERS, the most frequently co-reported reaction terms for Temozolomide are thrombocytopenia, nausea, fatigue, neutropenia, vomiting, febrile neutropenia. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Temozolomide have an FDA boxed warning?

No. The FDA label retrieved for Temozolomide has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Temozolomide causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID 021b97cc-a76f-44b6-b7be-670d2ae83690, effective 20260609; matched on openfda.generic_name.exact:"TEMOZOLOMIDE")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 1,047 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath
ClinicalTrials.gov API v2 (query TEMOZOLOMIDE, results-bearing studies sorted by enrollment)

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.