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Methimazole

Detailed information about Methimazole

Official label facts Owner quick guide first Marketing clearly labeled
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Reviewed / Updated / Sources

Reviewed: Not available

Updated: February 12, 2026, 7:40 PM UTC

Sources:

Pet Owner Quick Guide

Start here first for the simple next-step summary.

Used for:

For the treatment of hyperthyroidism in cats.

What to watch for:

  • Use caution with liver disease, blood disorders, or autoimmune conditions
  • Weight loss (1 reports)
  • Urinary tract infection (1 reports)
  • very low energy (1 reports)

When to call the vet:

  • Repeated vomiting or diarrhea.
  • Severe lethargy (hard to wake, very low energy).
  • Collapse or fainting.
  • Trouble breathing.
  • Facial swelling or hives.
  • Blood in vomit or stool.

What to ask your vet today:

  • Is this medicine the right fit for my pet’s current symptoms?
  • Which warning signs mean I should call back right away?
  • How should I handle missed doses or refusal to take the medicine?
Safety & side effects

What to watch:

  • Use caution with liver disease, blood disorders, or autoimmune conditions
  • Weight loss
  • Urinary tract infection
  • very low energy

Most reported reactions:

  • Weight loss (1 reports)
  • Urinary tract infection (1 reports)
  • Tiredness (lethargy) (1 reports)

When to call your vet:

  • Repeated vomiting or diarrhea.
  • Severe lethargy (hard to wake, very low energy).
  • Collapse or fainting.
  • Trouble breathing.
Talk to a Vet / Find a Vet Near You Start Symptom Intake

Data freshness: source data appears current.

Latest refresh: Mar 21, 2026, 10:01 a.m.

Data freshness
  • Medication catalog: Source Roxee | Refreshed Feb 12, 2026, 7:40 PM UTC
  • Animal Drugs @ FDA: Source FDA | Refreshed Mar 21, 2026, 10:00 AM UTC
    Applications/products are imported from FDA export data.
  • Animal Drugs @ FDA previews: Source FDA | Refreshed Feb 9, 2026, 3:05 AM UTC
    Label highlights/doc links are fetched from FDA preview endpoints.
  • Animal Drug Product Listing Directory (NDC): Source FDA | Refreshed Mar 21, 2026, 10:01 AM UTC
    Package/product NDCs from FDA’s electronic listing directory (XLS).
  • openFDA reaction terms: Source FDA openFDA | Refreshed Mar 18, 2026, 10:03 AM UTC
  • openFDA case summaries: Source FDA openFDA | Refreshed Feb 17, 2026, 11:05 AM UTC
Image for Methimazole

Methimazole

Drug type: Generic ingredient • Branded profile • FDA branded products available

Species: Cat

Manufacturer: Not available (source)

Quick Facts

Official label facts first, then secondary summaries. Marketing content is separated below.

Species: Cat
Manufacturer: Not available
Form: Coated Tablets, Oral Solution
Identifiers:
ANADA: 200771 ANADA: 200814 NADA: 141292 NDC Package: 11695-7048-1 NDC Package: 11695-7049-1 NDC Package: 17033-225-10 NDC Package: 17033-250-10 NDC Package: 55529-170-02 NDC Package: 55529-170-14 NDC Package: 86032-064-01 NDC Package: 86101-059-11 NDC Package: 86101-060-11 NDC Package: 86136-157-36 NDC Package: 86136-158-36 NDC Product: 11695 NDC Product: 17033 NDC Product: 55529 NDC Product: 86032 NDC Product: 86101 NDC Product: 86136
Source metadata:

Warnings / Contraindications

Use caution with liver disease, blood disorders, or autoimmune conditions.

  • High: Use caution with liver disease, blood disorders, or autoimmune conditions.
Source metadata:

Adverse Reactions

Snapshot first, detailed rows second. This section summarizes signal data and is not a diagnosis.

Tap or hover a reaction to see what it means in plain language.

Tracked signals
25
Reported cases
21
Serious reports
16
Species represented
2
Grouped by Body System
Digestive (3) · Vomiting, Decreased appetite, Loss of appetite Neurologic (3) · Unsteady walking (ataxia), Tiredness (lethargy), Neurological signs NOS Effectiveness (2) · Lack of efficacy - NOS, Lack of efficacy (ectoparasite) - NOS Other (17) · Weight loss, Urinary tract infection, Shaking
Most Reported Reactions
Reaction Body system Cases Species Serious cases
Other 1 Cat 1
Other 1 Cat 1
Neurologic 1 Cat 1
Other 1 Cat 1
Other 1 Cat 1
Neurologic 1 Cat 1
Other 1 Cat 1
Other 1 Cat 1

Species coverage: Cat (24) Dog (1)

View detailed reaction table
Reaction Body system Species Seriousness Frequency Reports
Other Cat Serious - 1
Digestive Dog Non-serious - 1
Other Cat Serious - 1
Neurologic Cat Non-serious - 1
Neurologic Cat Serious - 1
Other Cat Non-serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Neurologic Cat Serious - 1
Effectiveness Cat Non-serious - 1
Effectiveness Cat Non-serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Digestive Cat Serious - 1
Other Cat Serious - 1
Digestive Cat Unknown - -
Other Cat Unknown - -
Other Cat Unknown - -
Other Cat Unknown - -
Source metadata:

Storage & Handling

Store at room temperature.

Documents

Owner handouts and official technical documents are grouped for faster access.

Owner handouts (0)
  • No owner handouts linked yet.
Official label / PI (0)
  • No official label or package insert links yet.
SPL (3)
  • Felanorm® · SPL
    https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/15866/Felanorm%C2%AE
  • Methimazole Coated Tablets · SPL
    https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/17489/Methimazole%20Coated%20Tablets
  • Felimazole® · SPL
    https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/2194/Felimazole%C2%AE
FOI (3)
Source metadata:
Veterinary reference (advanced)

Canonical medication sections are above. This legacy block remains available for deeper cross-reference without cluttering the primary workflow.

At a Glance

Quick facts and links to official labeling and safety signals.

Data freshness
  • Medication catalog: Source Roxee | Refreshed Feb 12, 2026, 7:40 PM UTC
  • Animal Drugs @ FDA: Source FDA | Refreshed Mar 21, 2026, 10:00 AM UTC
    Applications/products are imported from FDA export data.
  • Animal Drugs @ FDA previews: Source FDA | Refreshed Feb 9, 2026, 3:05 AM UTC
    Label highlights/doc links are fetched from FDA preview endpoints.
  • Animal Drug Product Listing Directory (NDC): Source FDA | Refreshed Mar 21, 2026, 10:01 AM UTC
    Package/product NDCs from FDA’s electronic listing directory (XLS).
  • openFDA reaction terms: Source FDA openFDA | Refreshed Mar 18, 2026, 10:03 AM UTC
  • openFDA case summaries: Source FDA openFDA | Refreshed Feb 17, 2026, 11:05 AM UTC
Official (FDA)
Identity: Generic ingredient • FDA branded products available
Official FDA brands: Felanorm® Felimazole® Methimazole Coated Tablets
Case-reported brands (openFDA): MSK
Catalog species: Cat • FDA-labeled species: Cat
Rx/OTC: RX
Form/route: Coated Tablets, Oral Solution • Oral
Applications: ANADA 200-771 • ANADA 200-814 • NADA 141-292
Documents: 3 (FOI: 3) • SPL: 3 • Label highlights • Official documents
Safety (openFDA)
Top reactions: Dog 1 • Cat 26 • View
Case summaries: 8 (showing 8) • View
openFDA reports are unverified and do not prove causation.
Explore
Linked using: Fda_Label (0.95), Fda_Label (0.95), Fda_Label (0.95)
Diagnosis Codes
ICD10_CM: E05.90
Thyrotoxicosis, unspecified without thyrotoxic crisis or storm

Counseling and Monitoring Highlights

Global Pet owner/Vet mode is controlled in the header. This section avoids duplicate in-page persona tabs.

Owner-facing counseling points
  • Use caution with liver disease, blood disorders, or autoimmune conditions. (Contraindication, High)
Top reaction signals
Weight loss (1) Urinary tract infection (1) Tiredness (lethargy) (1) Open mouth breathing (1) Not himself/herself (1) Neurological signs NOS (1) Joint pain (1) Hiding (1)

Identifiers & Packages

Normalized identifiers (NDC/NADA/ANADA) and package metadata from regulator listings.

Identifiers
ANADA: 200771 ANADA: 200814 NADA: 141292 NDC Package: 11695-7048-1 NDC Package: 11695-7049-1 NDC Package: 17033-225-10 NDC Package: 17033-250-10 NDC Package: 55529-170-02 NDC Package: 55529-170-14 NDC Package: 86032-064-01 NDC Package: 86101-059-11 NDC Package: 86101-060-11 NDC Package: 86136-157-36 NDC Package: 86136-158-36 NDC Product: 11695 NDC Product: 17033 NDC Product: 55529 NDC Product: 86032 NDC Product: 86101 NDC Product: 86136
Package NDC Product NDC Form / Route Status
11695-7048-1 11695 -
11695-7049-1 11695 -
17033-225-10 17033 -
17033-250-10 17033 -
55529-170-02 55529 -
55529-170-14 55529 -
86032-064-01 86032 -
86101-059-11 86101 -
86101-060-11 86101 -
86136-157-36 86136 -
86136-158-36 86136 -

Enriched Documents

Documents are tiered by source trust: Official, Clinical, Manufacturer, Marketing.

Data Sources & Change Log

Every non-trivial field is expected to include provenance and update timestamps.

Official 6 Clinical 2 Manufacturer 0 Marketing 0
Current Field Facts
  • overdose_info: Overdose may intensify side effects and can lead to overt hypothyroidism. Supportive care is required if an overdose occurs. (Clinical, 2026-02-12)
  • storage_handling: Store at room temperature. (Clinical, 2026-02-12)
  • contraindications: Use caution with liver disease, blood disorders, or autoimmune conditions. (Official, 2026-02-12)
  • side_effects: Vomiting, decreased appetite, lethargy, facial itching. Rare: low blood cell counts. (Official, 2026-02-12)
  • usage: Used to manage hyperthyroidism in cats. (Official, 2026-02-12)
Recent Revisions
  • side_effects updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields
  • contraindications updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields
  • usage updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields

FDA Products & Applications (Animal Drugs @ FDA)

Official sponsor/proprietary-name/application-status records linked by active ingredient.

Product Sponsor Application Status Published
Felanorm®
RX
Methimazole
Oral Solution • Oral
Label highlights
Official documents
Virbac AH, Inc. ANADA 200-771 Approved Jan 26, 2026
Methimazole Coated Tablets
RX
Methimazole
Coated Tablets • Oral
Label highlights
Official documents
Felix Pharmaceuticals Pvt. Ltd. ANADA 200-814 Approved Jul 1, 2025
Felimazole®
RX
Methimazole
Coated Tablets • Oral
Label highlights
Official documents
Dechra, Ltd. NADA 141-292 Approved Aug 8, 2019

Data source: FDA Animal Drugs @ FDA (public search export).

What It's For (FDA Label Highlights)

Extracted from FDA Animal Drugs @ FDA product labeling. Always confirm details with your veterinarian.

Composition / specifications
5 mg/mL
Cats
Indication

For the treatment of hyperthyroidism in cats.

Dosage

The starting dose is 2.5 mg administered every 12 hours. Following 3 weeks of treatment, the dose should be titrated to effect based on individual serum total T4 (TT4) levels and clinical response. Dose adjustments should be made in 2.5 mg increments. The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration.

Limitations

FDA page: Open in Animal Drugs @ FDA

Composition / specifications
2.5 mg or 5 mg methimazole per tablet
Cats
Indication

For the treatment of hyperthyroidism in cats.

Dosage

The starting dose of Methimazole Coated Tablets is 2.5 mg administered every 12 hours. Following 3 weeks of treatment, the dose should be titrated to effect based on individual serum total T4 (TT4) levels and clinical response. Dose adjustments should be made in 2.5 mg increments. The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration.

Limitations

FDA page: Open in Animal Drugs @ FDA

Species: Cat, No Use Class Stated Or Implied
Cats
Indication
For the treatment of hyperthyroidism in cats.
Dosage
The starting dose is 2.5 mg administered every 12 hours. Following three weeks of treatment, the dose should be titrated to effect based on individual serum total T4 (TT4) levels and clinical response. Dose adjustments should be made in 2.5 mg increments. The maximum total dosage is 20 mg per day divided, not to exceed 10 mg as a single administration.
Limitations
Due to potentially serious adverse reactions such as hepatopathy, immune-mediated anemia, thrombocytopenia, and agranulocytosis, cats on methimazole therapy should be monitored closely for any sign of illness including anorexia, vomiting, head/facial pruritus or edema, depression/lethargy, weight loss, anemia, skin lesions, diarrhea, fever, or lymphadenopathy. If a cat becomes ill while on FELIMAZOLE Coated Tablets, the drug should be stopped and appropriate hematological and biochemical testing should be done (see ANIMAL SAFETY and POST APPROVAL EXPERIENCE).

FDA page: Open in Animal Drugs @ FDA

Official Documents (FDA)

Direct links to FDA-hosted PDFs and SPL packages (when available).

Documents
SPL Packages

FDA page: Open in Animal Drugs @ FDA

Documents
SPL Packages

FDA page: Open in Animal Drugs @ FDA

Documents
  • Summary
    For the treatment of hyperthyroidism in cats.
SPL Packages

FDA page: Open in Animal Drugs @ FDA

Usage

Used to manage hyperthyroidism in cats.

Source: FDA Animal Drugs @ FDA • Reference

Contraindications

Use caution with liver disease, blood disorders, or autoimmune conditions.

Side Effects

Vomiting, decreased appetite, lethargy, facial itching. Rare: low blood cell counts.

Source: FDA openFDA • Reference

Top Reported Reactions (openFDA)

De-duplicated reaction terms grouped by body system from FDA openFDA reports (not verified; does not prove causation).

Digestive
Vomiting (1) • Dog Decreased appetite (1) • Cat Loss of appetite • Cat

Showing top 5 for Digestive.

Neurologic
Unsteady walking (1) • Cat Tiredness (1) • Cat Neurological signs NOS (1) • Cat

Showing top 5 for Neurologic.

Effectiveness
Lack of efficacy - NOS (1) • Cat Lack of efficacy (ectoparasite) - NOS (1) • Cat

Showing top 5 for Effectiveness.

Other
Weight loss (1) • Cat Urinary tract infection (1) • Cat Shaking (1) • Cat Open mouth breathing (1) • Cat Not himself/herself (1) • Cat
Show more (12)
Joint pain (1) • Cat Hiding (1) • Cat General illness (1) • Cat Gait abnormality (1) • Cat Fever (1) • Cat Elevated symmetrical dimethylarginine (1) • Cat Elevated creatinine (1) • Cat Decreased haematocrit (1) • Cat Death (1) • Cat Death by euthanasia • Cat Cold feeling to the touch • Cat Abnormal radiograph finding • Cat

Showing top 5 for Other.

Data source: FDA openFDA Animal & Veterinary adverse event reports.

Adverse Event Case Summaries (openFDA)

These are individual FDA adverse event reports. They are unverified and do not prove the medication caused the reaction.

Cat, Cat (unknown), Female, 20.5 year • Drug: MSK, Unassigned, Unknown • Reactions: General illness, Hiding, Joint pain, Elevated creatinine, Elevated symmetrical dimethylarginine… • Outcome: Outcome Unknown

  • Report ID: USA-USFDACVM-2025-US-055646
  • Serious AE: Yes
  • Treated For AE: Yes
  • Sex: Female
  • Age: 20.50 Year
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Unknown
  • Form: Unassigned
Reactions Reported:
General illness Hiding Joint pain Elevated creatinine Elevated symmetrical dimethylarginine Decreased haematocrit Urinary tract infection
Outcomes: Outcome Unknown

Cat, Cat (unknown), Female, 13 year, 3.311 kilogram • Drug: MSK • Reactions: Lack of efficacy - NOS, Urinary tract infection • Outcome: Outcome Unknown

  • Report ID: USA-USFDACVM-2025-US-055723
  • Serious AE: No
  • Treated For AE: No
  • Sex: Female
  • Age: 13.00 Year
  • Weight: 3.311 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
Reactions Reported:
Lack of efficacy - NOS Urinary tract infection
Outcomes: Outcome Unknown

Cat, Domestic Shorthair, Female, 16 year, 3.946 kilogram • Drug: MSK, Unassigned, Unknown • Reactions: Shaking • Outcome: Ongoing

  • Report ID: USA-USFDACVM-2025-US-054883
  • Serious AE: No
  • Treated For AE: No
  • Sex: Female
  • Age: 16.00 Year
  • Weight: 3.946 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Unknown
  • Form: Unassigned
Reactions Reported:
Shaking
Outcomes: Ongoing

Cat, Domestic Shorthair, Male, 19 year, 4.717 kilogram • Drug: MSK, Unassigned, Oral • Reactions: Open mouth breathing, Not himself/herself, Neurological signs NOS, Death • Outcome: Died

  • Report ID: USA-USFDACVM-2025-US-055031
  • Serious AE: Yes
  • Treated For AE: Yes
  • Sex: Male
  • Age: 19.00 Year
  • Weight: 4.717 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Oral
  • Form: Unassigned
Reactions Reported:
Open mouth breathing Not himself/herself Neurological signs NOS Death
Outcomes: Died

Cat, Domestic Shorthair, Male, 12 year, 5.443 kilogram • Drug: MSK, Solution, Oral, Dose: 2.50 Milligram per dose, Frequency: 12 per hour • Reactions: Fever, Tiredness (lethargy), Gait abnormality, Decreased appetite, Weight loss • Outcome: Outcome Unknown

  • Report ID: USA-USFDACVM-2025-US-055468
  • Serious AE: Yes
  • Treated For AE: Yes
  • Sex: Male
  • Age: 12.00 Year
  • Weight: 5.443 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Oral
  • Form: Solution
  • Dose: 2.50 Milligram per dose
  • Frequency: 12 per hour
Reactions Reported:
Fever Tiredness (lethargy) Gait abnormality Decreased appetite Weight loss
Outcomes: Outcome Unknown

Cat, Domestic Longhair, Female, 15 year, 4.681 kilogram • Drug: MSK, Unassigned, Unknown • Reactions: Unsteady walking (ataxia) • Outcome: Recovered/Normal

  • Report ID: USA-USFDACVM-2025-US-053619
  • Serious AE: No
  • Treated For AE: No
  • Sex: Female
  • Age: 15.00 Year
  • Weight: 4.681 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Unknown
  • Form: Unassigned
Reactions Reported:
Unsteady walking (ataxia)
Outcomes: Recovered/Normal

Cat, ['Siamese', 'Mixed (Cat)'], Female, 16 year, 4.12 kilogram • Drug: MSK, Unknown • Reactions: Lack of efficacy (ectoparasite) - NOS • Outcome: Outcome Unknown

  • Report ID: USA-USFDACVM-2025-US-054123
  • Serious AE: No
  • Treated For AE: No
  • Sex: Female
  • Age: 16.00 Year
  • Weight: 4.120 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Unknown
Reactions Reported:
Lack of efficacy (ectoparasite) - NOS
Outcomes: Outcome Unknown

Dog, ['Shepherd Dog - Australian', 'Collie - Border'], Female, 12 year, 14.969 kilogram • Drug: MSK, Unassigned, Unknown, Dose: 5 Milligram per animal, Frequency: 12 per hour • Reactions: Vomiting • Outcome: Ongoing

  • Report ID: USA-USFDACVM-2025-US-033131
  • Serious AE: No
  • Treated For AE: No
  • Sex: Female
  • Age: 12.00 Year
  • Weight: 14.969 Kilogram
  • Case-reported brand: MSK
  • Case-reported manufacturer: MSK
  • Route: Unknown
  • Form: Unassigned
  • Dose: 5 Milligram per animal
  • Frequency: 12 per hour
Reactions Reported:
Vomiting
Outcomes: Ongoing

Data source: FDA openFDA Animal & Veterinary adverse event reports.

Overdose Information

Overdose may intensify side effects and can lead to overt hypothyroidism. Supportive care is required if an overdose occurs.

Storage & Handling

Store at room temperature.

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