Breed · Dog

Jack Russell Terrier: adverse event reports

FDA breed label "Terrier - Jack Russell" · single-breed animals only

Read this first · FDA's caveat, in its words

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

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Not veterinary advice. This site lists what was reported to FDA. For an animal that is unwell, contact a veterinarian.

10,504reports, 1990–20261.1% of dog reports

286reports, 12 months to March 2026309 in the 12 months before

37.4%classed serious, as reportedall dogs: 38.3%

15.2%name milbemycin oxime + spinosadall dogs: 13.1%

10,504 adverse event reports received by FDA describe an animal recorded as Jack Russell Terrier (FDA breed label "Terrier - Jack Russell"). That is 1.1% of all reports about dogs. Crossbred animals are not counted here, only reports that give this single breed.

286 reports arrived in the 12 months to March 2026, close to the 309 of the 12 months before. A breed's count mostly mirrors how common the breed is; registration and ownership figures by breed are not public data, so no per-animal rate can be given.

By active ingredient, the drugs named most often are milbemycin oxime + spinosad, ivermectin + pyrantel pamoate and spinosad. Milbemycin Oxime + Spinosad is named in 15.2% of this breed's reports, about the same share as in reports about all dogs (13.1%).

The terms listed most often are vomiting (21.5%), lethargy (8.6%) and lack of efficacy (ectoparasite) - flea (7.9%). Vomiting appears in 21.5% of reports, about the same share as in all dog reports (19.7%). 37.4% of reports stating seriousness were classed as serious, against 38.3% for dogs overall.

Drugs named most often, by active ingredient

Active ingredients recorded for the drug	Reports	Share of Jack Russell Terrier reports	Share of all dog reports
Milbemycin Oxime + Spinosad	1,595	15.2%	13.1%
Ivermectin + Pyrantel Pamoate	1,302	12.4%	14.9%
Spinosad	1,043	9.9%	5.8%
Fluralaner	630	6%	6.7%
Moxidectin	582	5.5%	5%
Afoxolaner	538	5.1%	5.7%
Oclacitinib	378	3.6%	2.9%
Selamectin	374	3.6%	3%
Milbemycin Oxime	363	3.5%	3%
Cyclosporine	344	3.3%	1.5%
Lufenuron + Milbemycin Oxime	297	2.8%	2.7%
Carprofen	293	2.8%	4.8%
Pyrantel Pamoate + Sarolaner	263	2.5%	5.1%
Melarsomine Dihydrochloride	204	1.9%	2.3%
Milbemycin Oxime + Praziquantel	195	1.9%	3.1%
Trilostane	185	1.8%	1.2%
Ivermectin	157	1.5%	1.3%
Imidacloprid + Moxidectin	154	1.5%	1.3%
Nitenpyram	148	1.4%	1.1%
Sarolaner	147	1.4%	1.7%

Ordered by report count. Differences from the species column often come from body size (which drugs a breed is prescribed) and from how common the breed was in the years a drug sold most. FDA states that these data cannot be used to estimate risk or to compare one product with another. Brand and manufacturer names are masked by FDA in these records.

Signs listed in reports

share of Jack Russell Terrier reports listing the termall dog reports

Vomiting21.5%2,256
Lethargy[unusually tired or inactive]8.6%904
Lack of efficacy (ectoparasite) - flea[the product did not have the expected effect: fleas]7.9%827
Emesis[vomiting]7.7%812
Diarrhoea[diarrhea]7%739
Ineffective, heartworm larvae[legacy FDA term: the product did not have the expected effect (heartworm larvae)]6.9%725
Lack of efficacy - NOS[the product did not have the expected effect]4.7%498
Anorexia[not eating]4.7%493
Lack of efficacy (endoparasite) - hookworm[the product did not have the expected effect: hookworms]4.4%467
Depression[dull, quiet or withdrawn]4.4%465
Pruritus[itching]3.4%362
Seizure NOS[seizure, type not specified]3.2%341
Ataxia[unsteady, uncoordinated movement]3.2%337
Elevated alanine aminotransferase (ALT)[a liver enzyme above the normal range]2.9%303
Lack of efficacy (endoparasite) - heartworm[the product did not have the expected effect: heartworm]2.8%298
Trembling2.5%262
Elevated serum alkaline phosphatase (SAP)[a liver and bone enzyme above the normal range]2.4%247
Behavioural disorder NOS[behaviour change, type not specified]2.3%243
Accidental exposure[exposure that was not intended]2.3%238
Shaking2.3%237
Death2.2%236
Death by euthanasia[the animal was euthanized]2%205
Ineffective, ascarids NOS[legacy FDA term: the product did not have the expected effect (ascarids nos)]1.9%195
Other abnormal test result NOS[abnormal laboratory result, type not specified]1.8%191
Digestive tract disorder NOS[digestive problem, type not specified]1.8%187

Age and weight

Age of the animal

Under 1 year7.5%786

1 to 3 years24.9%2,619

4 to 7 years24.8%2,607

8 to 11 years21.8%2,290

12 years and over17.5%1,843

Age not given3.4%359

Weight of the animal

Under 5 kg (11 lb)10.4%1,097

5 to 9.9 kg (11–22 lb)66.7%7,004

10 to 24.9 kg (22–55 lb)19.2%2,017

25 to 44.9 kg (55–99 lb)0.1%9

45 kg and over (99 lb+)0.1%6

Weight not given3.5%371

Coloured bar: Jack Russell Terrier reports. Grey bar: all dog reports.

Trend and outcomes

Reports by month FDA received them. The newest months are incomplete because FDA posts reports with a delay of three to six months.

Outcome recorded in the report

Recovered/Normal25.2%2,642

Recovered with Sequela3%314

Ongoing15.8%1,662

Died3%315

Euthanized1.4%144

Outcome Unknown23.1%2,422

Beside all dogs

Measure	Jack Russell Terrier	All dogs
Reports	10,504	985,675
Latest 12 months	286	53,292
Classed serious, of reports stating it	37.4%	38.3%
Death or euthanasia recorded, per 1,000 reports	43.7	55

Questions about Jack Russell Terrier reports

How many FDA adverse event reports involve Jack Russell Terriers?

10,504 reports through March 2026, 1.1% of reports about dogs; 286 in the latest 12 months.

Which drugs are named most often in Jack Russell Terrier reports?

By active ingredient: milbemycin oxime + spinosad (1,595), ivermectin + pyrantel pamoate (1,302), spinosad (1,043), fluralaner (630) and moxidectin (582). Brands are masked in the public data.

What signs are reported most for this breed?

vomiting (21.5%), lethargy (8.6%), lack of efficacy (ectoparasite) - flea (7.9%), emesis (7.7%) and diarrhoea (7%).

Is the Jack Russell Terrier more sensitive to certain drugs?

Report counts cannot answer that. They show what was reported, not what a drug did, and they are not adjusted for how many Jack Russell Terrier animals exist or were treated. Breed-related drug sensitivities that are established are described on FDA-approved labels; a veterinarian is the person to ask about an individual animal.

Why are crossbreds not included?

FDA records crossbred animals with one or more component breeds. Counting them under each component would double count, so breed pages use single-breed reports only. Crossbreds remain in the species totals.

How do I report a problem?

Call the drug company using the number on the label, or send Form FDA 1932a to FDA. See the guide on how to report.

Where this comes from. Counts are built from the openFDA Animal & Veterinary adverse event bulk files released 28 Sep 2026, which hold reports FDA's Center for Veterinary Medicine received through 31 Mar 2026. openFDA masks brand and manufacturer names in these files, so drugs are counted by the active ingredients each record discloses and no figure is attributed to a brand, application or company. Ingredient names, and the separate reference lists of approved products, follow the FDA Green Book as of 1 Oct 2026. Breed names are FDA's labels rearranged into everyday order ("Terrier - Jack Russell" becomes "Jack Russell Terrier"). No report text, lot numbers or reporter details are published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.