pharmacopeia
GET
/api/v1/drug/methimazole
2D structure
3-methyl-1H-imidazole-2-thione
SMILES CN1C=CNC1=S
InChIKey PMRYVIKBURPHAH-UHFFFAOYSA-N

Mechanism of action

Sourced from openFDA

Mechanism-of-action classes: Organic Anion Transporter Interactions; Protein Synthesis Inhibitors; Thyroid Hormone Synthesis Inhibitors; Uncouplers.

Protein SynthesisThyroid Hormone Synthesis

Indications

Sourced from openFDA
  • AND USAGE

Contraindications

Sourced from openFDA
  • CONTRAINDICATIONScontraindicated

Dosage & administration

Sourced from openFDA

DOSAGE AND ADMINISTRATION

Warnings & precautions

Sourced from openFDA

First Trimester Use of Methimazole and Congenital Malformations Methimazole crosses the placental membranes and can cause fetal harm when administered in the first trimester of pregnancy. Rare instances of congenital defects, including aplasia cutis, craniofacial malformations (facial dysmorphism; choanal atresia), gastrointestinal malformations (esophageal atresia with or without tracheoesophageal fistula), omphalocele and abnormalities of the omphalomesenteric duct have occurred in infants born to mothers who received methimazole in the first trimester of pregnancy. If methimazole is used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the potential hazard to the fetus. Because of the risk for congenital malformations associated with use of methimazole in the first trimester of pregnancy, it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism. If methimazole is used, the lowest possible dose to control the maternal disease should be given. Agranulocytosis Agranulocytosis is a potentially life-threatening adverse reaction of methimazole therapy. Patients should be instructed to immediately report to their physicians any symptoms suggestive of agranulocytosis, such as fever or sore throat. Leukopenia, thrombocytopenia, and aplastic anemia (pancytopenia) may also occur. The drug should be discontinued in the presence of agranulocytosis or aplastic anemia (pancytopenia), and the patient's bone marrow indices should be monitored.

Adverse reactions

Sourced from openFDA

ADVERSE REACTIONS

Use in specific populations

Sourced from openFDA

Pregnancy (See WARNINGS ) If methimazole is used during the first trimester of pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the potential hazard to the fetus. In pregnant women with untreated or inadequately treated Graves' disease, there is an increased risk of adverse events of maternal heart failure, spontaneous abortion, preterm birth, stillbirth and fetal or neonatal hyperthyroidism. Because methimazole crosses placental membranes and can induce goiter and cretinism in the developing fetus, hyperthyroidism should be closely monitored in pregnant women and treatment adjusted such that a sufficient, but not excessive, dose be given during pregnancy. In many pregnant women, the thyroid dysfunction diminishes as the pregnancy proceeds; consequently, a reduction of dosage may be possible. In some instances, anti-thyroid therapy can be discontinued several weeks or months before delivery. Due to the rare occurrence of congenital malformations associated with methimazole use, it may be appropriate to use an alternative anti-thyroid medication in pregnant women requiring treatment for hyperthyroidism, particularly in the first trimester of pregnancy during organogenesis.

Overdosage

Sourced from openFDA

Signs and Symptoms Symptoms may include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema. Aplastic anemia (pancytopenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression. No information is available on the median lethal dose of the drug or the concentration of methimazole in biologic fluids associated with toxicity and/or death. Treatment To obtain up-to-date information about the treatment of overdose, a good resource is your certified Regional Poison Control Center. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in the patient. In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient's medical status.

Approval history

Sourced from openFDA
  • Mar 29, 2000ANDAANDA040350Mylan
  • Mar 27, 2001ANDAANDA040411Chartwell Rx
  • Feb 18, 2005ANDAANDA040547Aiping Pharm Inc
  • Dec 14, 2007ANDAANDA040734Heritage Pharma
  • Mar 7, 2012ANDAANDA202068Rising
  • May 24, 2023ANDAANDA209827Macleods Pharms Ltd
  • Sep 25, 2023ANDAANDA218149Bionpharma
  • Feb 5, 2025ANDAANDA218830Square Pharms Plc

FAERS reports

View JSON
Reference statistics only. FAERS reports are voluntarily submitted and are not incidence rates, safety signals, or causal evidence. Counts reflect reporting volume — how often a reaction was reported, not how often it occurs. For decision-grade use, consult openFDA and the FAERS Public Dashboard directly.
7,577 total reports matchedLatest report Share = reports listing the reaction ÷ total matched reports. Rows can sum to >100% because a single report often lists multiple reactions.
  1. 1Drug Ineffective6278.3%
  2. 2Off Label Use4726.2%
  3. 3Fatigue4375.8%
  4. 4Hyperthyroidism3985.3%
  5. 5Nausea3765.0%
  6. 6Diarrhoea3304.4%
  7. 7Headache3244.3%
  8. 8Pain3034.0%
  9. 9Dizziness3024.0%
  10. 10Dyspnoea2703.6%
  11. 11Agranulocytosis2533.3%
  12. 12Asthenia2162.9%
  13. 13Arthralgia2152.8%
  14. 14Anxiety2112.8%
  15. 15Rash2092.8%

Literature

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Recent PubMed references pinned to Methimazole as a MeSH major topic. Citations link to pubmed.ncbi.nlm.nih.gov.

Clinical trials

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The 10 most recently updated of 39 ClinicalTrials.gov registrations naming Methimazole as an intervention. Registration is not evidence of efficacy or safety — reference crosswalk only.

Pharmacogenomics

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CPIC-curated drug–gene pairs for Methimazole. Levels describe the strength of curated evidence and guideline status — never a recommendation to test or to adjust therapy.

  • HLA-BCPIC C (provisional)ClinPGx 3

Frequently asked questions

How does Methimazole work?
Mechanism-of-action classes: Organic Anion Transporter Interactions; Protein Synthesis Inhibitors; Thyroid Hormone Synthesis Inhibitors; Uncouplers.
What is Methimazole used for?
According to FDA labeling, Methimazole carries indications including: AND USAGE. This is a reference summary of labeled uses, not medical advice or a treatment recommendation.
What class of drug is Methimazole?
Methimazole is classified as Sulfur-containing imidazole derivatives, Thyroid Hormone Synthesis Inhibitor, Organic Anion Transporter Interactions, Protein Synthesis Inhibitors, Thyroid Hormone Synthesis Inhibitors, Uncouplers, Decreased Iodine Organification, Decreased Protein Modification, Decreased Protein Synthesis, Decreased Thyroid Hormone Iodination.
What are the brand names for Methimazole?
Methimazole is marketed under brand names including Felanorm, Felimazole, Reguzol.
What are the contraindications for Methimazole?
Methimazole labeling lists contraindications including: CONTRAINDICATIONS. Always consult the full prescribing information and a clinician.
Note. Data for methimazole is illustrative MVP content compiled from public sources. pharmacopeia is for educational and informational use only and is not a substitute for professional medical advice.

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