Pet Drug Reports

Methimazole (Felimazole, Felanorm)adverse event reports that FDA received

Active ingredient

The names in brackets are brand names with this active ingredient.

The openFDA records give the value "MSK" for the brand name and for the manufacturer name of each drug. FDA says that MSK means "masked". So the site cannot count a report for a brand.

Read this first. FDA says this about the data:

An API dataset query result cannot be used to estimate the risk associated with the product or compare one drug or device product with another. When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event. This dataset should not be the sole source of information for clinical decision-making or other assumptions about the safety or effectiveness of a product. The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.

FDA Center for Veterinary Medicine publishes these words. Source: Adverse Event Reports for Animal Drugs and Devices, read on . The data have the reports that FDA received through .

This page is not veterinary advice. For an animal that is ill, speak to a veterinarian.

Contacting a veterinarianHow to report to FDA

From August 1998 to June 2026, FDA received 1,283 adverse event reports that name a drug with methimazole as its active ingredient. Of the 1,283 reports, 1,249 (97.3%) are about cats.

In January to March 2026, FDA received 60 reports that name this drug. The signs that appear in the largest number of the 1,283 reports are "Vomiting", "Lethargy" and "Weight loss". A report is not proof that a drug caused a sign.

Reports that name this drug rose by 4.0% in the 12 months to June 2026, compared with the 12 months before. Reports for all animal drugs fell by 4.6% in the same periods. The newest months can get more reports in a later update. Reports about cats are 97.3% of the reports that name this drug, and 11% of all reports.

Since the last update of the FDA data

The latest update of the FDA data, recorded on , changed no count of this page.

January to March 2026 is the latest closed quarter in the data. In that quarter FDA received 60 reports that name methimazole: 1 dog, 59 cat, 0 horse, 0 other or not given.

All updatesFeed of updates (RSS)

Signs that the reports list

A sign is a coded term from the report. The words in brackets are a plain gloss of the term. The percentage is the share of the 1,283 reports that list the sign. One report can list more than one sign.

The sign that is in the largest number of the reports comes first.

  1. Vomiting16.6%213 reports
  2. Lethargy[unusually tired or inactive]15.2%195 reports
  3. Weight loss11.7%150 reports
  4. Lack of efficacy - NOS[the product did not have the expected effect]9.1%117 reports
  5. Anorexia[not eating]8.9%114 reports
  6. Not eating8.6%110 reports
  7. Death by euthanasia[the animal was euthanized]7.1%91 reports
  8. Diarrhoea[diarrhea]6.5%83 reports
  9. Decreased appetite6%77 reports
  10. Ataxia[unsteady, uncoordinated movement]5.8%74 reports
  11. Behavioural disorder NOS[behaviour change, type not specified]5.5%70 reports
  12. Death5.3%68 reports
  13. Dehydration5%64 reports
  14. Vocalisation[crying out or unusual noise]5%64 reports
Show the next 16 signs
  1. Elevated blood urea nitrogen (BUN)[a kidney value above the normal range]4.2%54 reports
  2. Pruritus[itching]4.2%54 reports
  3. Hiding4%51 reports
  4. Other abnormal test result NOS[abnormal laboratory result, type not specified]3.9%50 reports
  5. Seizure NOS[seizure, type not specified]3.7%48 reports
  6. Skin scab3.7%47 reports
  7. Anaemia NOS[low red blood cell count]3.6%46 reports
  8. Elevated creatinine[a kidney value above the normal range]3.5%45 reports
  9. Elevated alanine aminotransferase (ALT)[a liver enzyme above the normal range]3.4%44 reports
  10. Emesis[vomiting]3.4%44 reports
  11. Emesis (multiple)[vomiting more than once]2.7%34 reports
  12. Not drinking2.7%34 reports
  13. Hyperglycaemia[high blood sugar]2.6%33 reports
  14. Ketosis[ketones building up in the body]2.6%33 reports
  15. Abnormal radiograph finding2.3%29 reports
  16. Dilated pupils2.2%28 reports

The list shows 30 of 867 coded signs. A report is not proof that a drug caused a sign. Download all signs (CSV)

Reports by species

  • Cat97.3%1,249
  • Dog0.4%5
  • Human exposure0.1%1

The share is of all 1,283 reports that name methimazole. The other reports give a different species or no species.

Reports for each month, Jul 2021 to Jun 2026

Dog4 reports

No chart: no month has 5 or more reports.

Cat812 reports. Largest count in one month: 25 (Dec 2025)
Horse0 reports

No chart: no month has 5 or more reports.

Other or not given26 reports

No chart: no month has 5 or more reports.

The month is the month in which FDA received the report. Each chart has its own scale. FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.

Reports by year

  • Dog
  • Cat
  • Horse
  • Other or not given
Reports that name methimazole, by the year in which FDA received them and by species
YearDogCatHorseOther or not givenAll species
2026311301117
20251244021266
2024020402206
2023016202164
20220620062
20210440044
20200400141
20190490049
20180420042
20170310031
20160370138
20150390039
20141290030
20130530154
20120390039
20110280028
201008008
200908008
200601001
200202002
20010120012
200001001
199801001

2026 has the reports that FDA received through Jun 2026. Download the years (CSV)

What the reports record

Outcome at the time of the report

  • Recovered/Normal20.3%261
  • Recovered with Sequela[recovered, with a lasting effect]1.2%15
  • Ongoing36.9%473
  • Died5.9%76
  • Euthanized7.1%91
  • Outcome Unknown22.8%293

An outcome in a report is not proof that the drug caused it. The person who sends the report gives the outcome. Each share is of the 1,283 reports that name methimazole.

A report about more than one animal can have more than one outcome.

Kind of report

  • Safety issue85.4%1,096
  • Lack of expected effectiveness4.9%63
  • Both safety and lack of expected effectiveness5.9%76
  • Manufacturing or product defect3.7%48
  • Other0%0

1,169 reports say if the event was serious. 50.2% of them have the serious flag. The person who sends the report sets the flag.

Show age, weight, breed and route

Age of the animal

  • Under 1 year0%0
  • 1 to 3 years0.2%3
  • 4 to 7 years1.2%16
  • 8 to 11 years12.2%156
  • 12 years and over81.6%1,047
  • Age not given4.8%61

Weight of the animal

  • Under 5 kg (11 lb)68%873
  • 5 to 9.9 kg (11 to 22 lb)23.9%307
  • 10 to 24.9 kg (22 to 55 lb)0.4%5
  • 25 to 44.9 kg (55 to 99 lb)0.2%2
  • 45 kg and over (99 lb and over)0.1%1
  • Weight not given7.4%95

Breed, where the report gives one breed

A breed with many animals has many reports.

Route in the report

  • Oral38.3%491
  • Topical5.6%72
  • Transdermal4.8%62
  • Other0.4%5
  • Auricular (Otic)0.3%4
  • Intradermal0.2%2

Each bar is on a scale of 0 to 100%.

Approved animal drugs with this active ingredient (FDA Green Book)

This section is reference data. It has no report count.

The openFDA records give the value "MSK" for the brand name and for the manufacturer name of each drug. FDA says that MSK means "masked". So the site cannot count a report for a brand.

Brand names

  • Felimazole
  • Felanorm

What the Green Book records give

Applications with an approval in force
4
Approved species
Cats
Dose forms
Coated Tablets, Oral Solution
Routes
Oral
Sale
RX (prescription)
Earliest approval date in the records

The species, dose forms and routes are the words of the Green Book records for all the applications together. One product can have fewer. The label of a product gives its approved use.

Applications in the Green Book of 2 Nov 2026, pioneer applications (NADA) first
Brand nameActive ingredientsSponsorApproved speciesApplication
FelimazoleMethimazoleDechra Veterinary Products LLCCatsNADA 141-292
FelanormMethimazoleVirbac AH, Inc.CatsANADA 200-771
Methimazole Coated TabletsMethimazoleFelix Pharmaceuticals Pvt. Ltd.CatsANADA 200-814
Methimazole Oral SolutionMethimazoleFelix Pharmaceuticals Pvt. Ltd.CatsANADA 200-860

Next in the A to Z list

All drugs by active ingredient. Brand names A to Z

FDA pages for this drug

The site checked these addresses on . The links open in a new tab.

Cite this page

Pet Drug Reports. Methimazole: adverse event reports that FDA received. https://petdrugreports.com/drug/methimazole/ Source: FDA Center for Veterinary Medicine, openFDA Animal and Veterinary adverse event reports, export of . Reports received through .

Embed this card on your site

Copy this code into your page. The card shows the figures above with their source. A line under the card links to this page.

How embedding works. It is free. Keep the link in the card and the link line under it.

Where the data come from

The counts come from the openFDA Animal and Veterinary adverse event files, export of 30 Oct 2026. The files have the reports that the FDA Center for Veterinary Medicine received through 26 Jun 2026. The files mask brand and manufacturer names. The site counts a drug by the active ingredients that each record gives, and gives no count to a brand, an application or a company. Ingredient names and the lists of approved products follow the FDA Green Book of 2 Nov 2026. The site does not use the application number that a record has.

The site does not publish report text, lot numbers or details of a reporter. FDA's record is the authority. See how the site counts reports, the data sources and the corrections page.

Questions about these reports

Which brand are these reports about?

The openFDA records give the value "MSK" for the brand name and for the manufacturer name of each drug. FDA says that MSK means "masked". So the site cannot count a report for a brand. The Green Book section of this page lists the brand names with this active ingredient.

Do the reports show that the drug caused the signs?

No. FDA states this about the data.

When looking at the results, be aware that there is no certainty that the reported drug or device caused the adverse event.

The adverse event may have been related to an underlying disease, other drugs used at the same time or other non-drug related sources.

FDA Center for Veterinary Medicine. Source: Adverse Event Reports for Animal Drugs and Devices

How many reports did FDA receive in the latest 12 months?

FDA received 257 reports in the 12 months to June 2026. It received 247 reports in the 12 months before. FDA says that a report can take 3 to 6 months to reach the public data. The newest months can get more reports in a later update.

What kinds of report are in the count?

Of the 1,283 reports received from August 1998 to June 2026, 85.4% are about a safety issue only. 10.8% are about a lack of expected effectiveness, alone or with a safety issue. 3.7% are about a defect of the product or its package.