Meds A-Z

Methimazole

Detailed information about Methimazole

Official label facts Owner quick guide first Marketing clearly labeled

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Pet Owner Quick Guide

Start here: what this medicine is for, what it does, and when it's usually needed.

Usually used for:

For the treatment of hyperthyroidism in cats.

What it does:

Used to manage hyperthyroidism in cats.

When it's needed:

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

Call your vet sooner if you notice:

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

Commonly reported reactions:

(1 reports)
(1 reports)
(1 reports)

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?

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Methimazole

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

Species: Cat

Manufacturer: MSK

Quick Facts

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

Species: Cat

Manufacturer: MSK

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 Product: 11695 NDC Product: 17033 NDC Product: 55529 NDC Product: 86032 NDC Product: 86101

Source metadata:

https://animaldrugsatfda.fda.gov/adafda/views/#/home/previewsearch/200771 · official_label · FDA application profile
https://animaldrugsatfda.fda.gov/adafda/views/#/home/previewsearch/200814 · official_label · FDA application profile
https://animaldrugsatfda.fda.gov · fda_animal_drugs · Medication usage source

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:

https://animaldrugsatfda.fda.gov · fda_animal_drugs · Contraindication source

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

Reported cases

Serious reports

Species represented

Most Reported Reactions

Cases	Species	Serious cases
1	Cat	1
1	Cat	1
1	Cat	1
1	Cat	1
1	Cat	1
1	Cat	1
1	Cat	1
1	Cat	1

Species coverage: Cat (31) Dog (1)

View detailed reaction table

Species	Seriousness	Frequency	Reports
Cat	Non-serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Non-serious	-	1
Cat	Non-serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Serious	-	1
Cat	Non-serious	-	1
Cat	Serious	-	1
Dog	Non-serious	-	1
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-
Cat	Unknown	-	-

Source metadata:

https://api.fda.gov/animalandveterinary/event.json · adverse_reaction · openFDA case USA-USFDACVM-2025-US-053619

Storage & Handling

Store at room temperature.

Source metadata: No source yet.

Documents

Official label facts are separated from secondary summaries.

Official documents: 6 • Secondary summaries: 0

Official label facts

FOI Summary oA 200-771 Approved July 8, 2024.pdf · FOI
Felanorm® · SPL
FOI Summary oA 200-814 Approved June 27, 2025.pdf · FOI
Methimazole Coated Tablets · SPL
UCM165091.pdf · FOI
Felimazole® · SPL

Secondary summaries

No source yet.

Source metadata:

https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/15625 · document · FOI
https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/15866/Felanorm%C2%AE · document · SPL
https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/17172 · document · FOI
https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/17489/Methimazole%20Coated%20Tablets · document · SPL
https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/857 · document · FOI
https://animaldrugsatfda.fda.gov/adafda/app/search/public/spl/file/2194/Felimazole%C2%AE · document · SPL

Promotional Materials (Marketing)

This content is marketing material and not clinical guidance.

No marketing assets are linked yet.

No source yet.

Source metadata: No source yet.

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Technical appendix (vet reference)

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 PetWisePlus | Refreshed Feb 12, 2026, 7:40 PM UTC
Animal Drugs @ FDA: Source FDA | Refreshed Feb 16, 2026, 11:00 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 Feb 16, 2026, 11:00 AM UTC
Package/product NDCs from FDA’s electronic listing directory (XLS).
openFDA reaction terms: Source FDA openFDA | Refreshed Feb 16, 2026, 11:01 AM UTC
openFDA case summaries: Source FDA openFDA | Refreshed Feb 12, 2026, 10:41 PM 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 56 • View

Case summaries: 7 (showing 7) • View

openFDA reports are unverified and do not prove causation.

Explore

Related conditions: Anemia (regenerative/non-regenerative) Hyperthyroidism Hyperthyroidism Pruritus (itching, undifferentiated) Thrombocytopenia (ITP) Weight loss

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

Ataxia (1) Death (1) Decreased haematocrit (1) Elevated creatinine (1) Elevated symmetrical dimethylarginine (SDMA) (1) General illness (1) Hiding (1) Joint pain (1) Lack of efficacy (ectoparasite) - NOS (1) Lack of efficacy - NOS (1) Neurological signs NOS (1) Not himself/herself (1) Open mouth breathing (1) Shaking (1) Urinary tract infection (1) Vomiting (1)

Identifiers & Packages

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

Identifiers

Package NDC	Product NDC	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	-

Enriched Documents

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

FOI Summary oA 200-771 Approved July 8, 2024.pdf • FOI summary • Official • Jan. 26, 2026
FDA FOI summary for application 200771
FOI Summary oA 200-814 Approved June 27, 2025.pdf • FOI summary • Official • July 1, 2025
FDA FOI summary for application 200814
UCM165091.pdf • FOI summary • Official • Aug. 8, 2019
FDA FOI summary for application 141292

Data Sources & Revision History

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

FOI FOI Summary oA 200-771 Approved July 8, 2024.pdf

Summary

For the treatment of hyperthyroidism in cats.

SPL Packages

Felanorm® (ZIP)

FDA page: Open in Animal Drugs @ FDA

Documents

FOI FOI Summary oA 200-814 Approved June 27, 2025.pdf

Summary

For the treatment of hyperthyroidism in cats.

SPL Packages

Methimazole Coated Tablets (ZIP)

FDA page: Open in Animal Drugs @ FDA

Documents

FOI UCM165091.pdf

Summary

For the treatment of hyperthyroidism in cats.

SPL Packages

Felimazole® (ZIP)

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)

Aggregated reaction terms from FDA openFDA reports (not verified; does not prove causation).

Dog

Digestive

Vomiting (1)

Cat

Digestive

Vomiting (128) Loss of appetite (64) Diarrhea (59) Loss of appetite (4) Loss of appetite (4) Loss of appetite (4) Loss of appetite (4) Loss of appetite (4) Loss of appetite (4)

Neurologic

Tiredness (lethargy) (81) Tiredness (lethargy) (3) Tiredness (lethargy) (3) Tiredness (lethargy) (3) Tiredness (lethargy) (3) Tiredness (lethargy) (3) Tiredness (lethargy) (3)

Effectiveness

Lack of efficacy - NOS (76) Lack of efficacy - NOS (4) Lack of efficacy - NOS (4) Lack of efficacy - NOS (4) Lack of efficacy - NOS (4) Lack of efficacy - NOS (4) Lack of efficacy - NOS (3)

Other

Weight loss (88) Not eating (76) Death by euthanasia (64) Weight loss (4) Weight loss (4) Weight loss (4) Weight loss (4) Weight loss (4) Intentional misuse (3) Intentional misuse (3) Intentional misuse (3) Intentional misuse (3) Intentional misuse (3) Intentional misuse (3) Medication error NOS (3) Medication error NOS (3) Medication error NOS (3) Medication error NOS (3) Medication error NOS (3) Medication error NOS (3) Not himself/herself (3) Not himself/herself (3) Not himself/herself (3) Not himself/herself (3) Not himself/herself (3) Not himself/herself (3) Weight loss (3) Abnormal radiograph finding (2) Abnormal radiograph finding (2) Abnormal radiograph finding (2) Abnormal radiograph finding (2) Abnormal radiograph finding (2) Abnormal radiograph finding (2)

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 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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Medical Disclaimer: The medication details provided on PetWisePlus are for informational purposes only and are not a substitute for professional veterinary advice. Always consult your veterinarian about your pet's specific needs.

Methimazole

Pet Owner Quick Guide

Methimazole

Quick Facts

Warnings / Contraindications

Adverse Reactions

Most Reported Reactions

Storage & Handling

Documents

Promotional Materials (Marketing)

At a Glance

Counseling and Monitoring Highlights

Identifiers & Packages

Enriched Documents

Data Sources & Revision History

FDA Products & Applications (Animal Drugs @ FDA)

What It's For (FDA Label Highlights)

Felanorm® • Oral Solution • Oral

Methimazole Coated Tablets • Coated Tablets • Oral

Felimazole® • Coated Tablets • Oral

Official Documents (FDA)

Felanorm® • 200771

Methimazole Coated Tablets • 200814

Felimazole® • 141292

Usage

Contraindications

Side Effects

Top Reported Reactions (openFDA)

Adverse Event Case Summaries (openFDA)

Sep 19, 2025 • Cat • Cat (unknown) • General illness, Hiding • Outcome Unknown

Sep 15, 2025 • Cat • Cat (unknown) • Lack of efficacy - NOS, Urinary tract infection • Outcome Unknown

Sep 11, 2025 • Cat • Domestic Shorthair • Shaking • Ongoing

Sep 11, 2025 • Cat • Domestic Shorthair • Open mouth breathing, Not himself/herself • Died

Sep 10, 2025 • Cat • Domestic Longhair • Unsteady walking (ataxia) • Recovered/Normal

Sep 10, 2025 • Cat • ['Siamese', 'Mixed (Cat)'] • Lack of efficacy (ectoparasite) - NOS • Outcome Unknown

Jun 12, 2025 • Dog • ['Shepherd Dog - Australian', 'Collie - Border'] • Vomiting • Ongoing

Overdose Information

Storage & Handling

Share Your Thoughts