Is Ivermectin safe for dogs?
The short answer
Ivermectin's safety in dogs splits cleanly along one genetic line. In dogs without the MDR1 mutation it has decades of use as a heartworm preventive and is generally well tolerated. In dogs carrying the MDR1 (ABCB1) mutation it cannot be cleared from the brain, and at the investigational oncology doses discussed here the resulting neurotoxicity can be fatal. Collies, Australian Shepherds, Shelties, Old English Sheepdogs, Border Collies and herding mixes are the high-risk populations. The cheek-swab test is inexpensive and must precede the first dose.
The critical risks
⚠ MDR1 gene mutation — testing is mandatory
Dogs carrying the MDR1 (ABCB1) mutation cannot clear ivermectin from the brain and suffer neurotoxicity at doses other dogs tolerate. At the investigational oncology doses discussed here, that reaction can be fatal. Affected breeds include Collies, Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, Border Collies, Long-haired Whippets, and any mixed breed with herding ancestry. The test is a simple cheek swab available through Washington State University and commercial laboratories. It must be done before the first dose.
Additional cautions
Neurological signs require immediate attention
Unsteadiness, dilated pupils, excessive drooling, disorientation, tremors, or blindness indicate ivermectin toxicity. Stop dosing and seek emergency veterinary care.
Breeds that require testing first
These breeds carry a genetic trait that changes how Ivermectin is handled. Testing must be completed before the first dose.
Border Collie — MDR1 (ABCB1) mutation risk — genetic testing required before ivermectin
This breed carries a meaningful frequency of the MDR1 gene mutation, which prevents the drug-efflux protein at the blood-brain barrier from clearing ivermectin out of the central nervous system. Affected dogs develop neurotoxicity at doses other dogs tolerate without difficulty, and at the investigational oncology doses discussed on this site that reaction can be fatal. A cheek-swab test through Washington State University or a commercial laboratory settles the question and must be done before the first dose.
Australian Shepherd — MDR1 (ABCB1) mutation risk — genetic testing required before ivermectin
This breed carries a meaningful frequency of the MDR1 gene mutation, which prevents the drug-efflux protein at the blood-brain barrier from clearing ivermectin out of the central nervous system. Affected dogs develop neurotoxicity at doses other dogs tolerate without difficulty, and at the investigational oncology doses discussed on this site that reaction can be fatal. A cheek-swab test through Washington State University or a commercial laboratory settles the question and must be done before the first dose.
Rough Collie — MDR1 (ABCB1) mutation risk — genetic testing required before ivermectin
This breed carries a meaningful frequency of the MDR1 gene mutation, which prevents the drug-efflux protein at the blood-brain barrier from clearing ivermectin out of the central nervous system. Affected dogs develop neurotoxicity at doses other dogs tolerate without difficulty, and at the investigational oncology doses discussed on this site that reaction can be fatal. A cheek-swab test through Washington State University or a commercial laboratory settles the question and must be done before the first dose.
Shetland Sheepdog — MDR1 (ABCB1) mutation risk — genetic testing required before ivermectin
This breed carries a meaningful frequency of the MDR1 gene mutation, which prevents the drug-efflux protein at the blood-brain barrier from clearing ivermectin out of the central nervous system. Affected dogs develop neurotoxicity at doses other dogs tolerate without difficulty, and at the investigational oncology doses discussed on this site that reaction can be fatal. A cheek-swab test through Washington State University or a commercial laboratory settles the question and must be done before the first dose.
Old English Sheepdog — MDR1 (ABCB1) mutation risk — genetic testing required before ivermectin
This breed carries a meaningful frequency of the MDR1 gene mutation, which prevents the drug-efflux protein at the blood-brain barrier from clearing ivermectin out of the central nervous system. Affected dogs develop neurotoxicity at doses other dogs tolerate without difficulty, and at the investigational oncology doses discussed on this site that reaction can be fatal. A cheek-swab test through Washington State University or a commercial laboratory settles the question and must be done before the first dose.
What the evidence base actually is
Safety claims are only as good as the studies behind them.
Ivermectin has been given to dogs as a heartworm preventive for decades, and its discovery earned a Nobel Prize. Separate research has investigated it in cancer models, where it appears to interfere with several signalling pathways cells use to survive and proliferate. One published study used canine mammary tumour cells specifically. It also carries the single most important breed-specific warning on this site.
Dosing context
Safety is dose-dependent. These are the figures reported in the source literature.
| Weight class | Reported dose | Frequency | Duration | Studied for |
|---|---|---|---|---|
| Small / toy breedunder 22 lb (10 kg) | 0.3-0.6 mg/kg per day | Daily, or five days on / two days off | 4-12+ weeks | Investigational oncology adjunct — MDR1 testing required first |
| Medium breed22–77 lb (10–35 kg) | 0.3-0.6 mg/kg per day | Daily, or five days on / two days off | 4-12+ weeks | Investigational oncology adjunct — MDR1 testing required first |
| Large / giant breedover 77 lb (35 kg) | 0.3-0.6 mg/kg per day | Daily, or five days on / two days off | 4-12+ weeks | Investigational oncology adjunct — MDR1 testing required first |
See the full Ivermectin profile for mechanism, protocol and monitoring detail.
Common questions
Is Ivermectin safe for dogs?+
Ivermectin's safety in dogs splits cleanly along one genetic line. In dogs without the MDR1 mutation it has decades of use as a heartworm preventive and is generally well tolerated. In dogs carrying the MDR1 (ABCB1) mutation it cannot be cleared from the brain, and at the investigational oncology doses discussed here the resulting neurotoxicity can be fatal. Collies, Australian Shepherds, Shelties, Old English Sheepdogs, Border Collies and herding mixes are the high-risk populations. The cheek-swab test is inexpensive and must precede the first dose.
What are the side effects of Ivermectin in dogs?+
MDR1 gene mutation — testing is mandatory: Dogs carrying the MDR1 (ABCB1) mutation cannot clear ivermectin from the brain and suffer neurotoxicity at doses other dogs tolerate. At the investigational oncology doses discussed here, that reaction can be fatal. Affected breeds include Collies, Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, Border Collies, Long-haired Whippets, and any mixed breed with herding ancestry. The test is a simple cheek swab available through Washington State University and commercial laboratories. It must be done before the first dose. Neurological signs require immediate attention: Unsteadiness, dilated pupils, excessive drooling, disorientation, tremors, or blindness indicate ivermectin toxicity. Stop dosing and seek emergency veterinary care.
Can Ivermectin be given to a dog with cancer?+
Ivermectin is among the compounds investigated as an adjunct in canine oncology rather than being contraindicated in it. That said, the evidence is investigational and this belongs entirely in the hands of a veterinary oncologist managing the specific case.
Does my dog need testing before starting Ivermectin?+
Yes, for some dogs. Border Collie, Australian Shepherd, Rough Collie, Shetland Sheepdog, Old English Sheepdog carry a genetic trait that changes how Ivermectin is handled, and testing must be completed before the first dose. Baseline bloodwork is also standard practice before starting any of the compounds covered on this site.
References
- 1.CANINE STUDYZhu M, et al. Ivermectin-induced apoptosis of canine mammary tumor cells through regulation of the cell cycle and WNT signaling. BMC Veterinary Research, 2019. PMC6679554
- 2.Juarez M, Schcolnik-Cabrera A, Duenas-Gonzalez A The multitargeted drug ivermectin: from an antiparasitic agent to a repositioned cancer drug. American Journal of Cancer Research, 2018. PMID 29344093
- 3.Tang M, et al. Ivermectin, a potential anticancer drug derived from an antiparasitic drug. Pharmacological Research, 2021. PMC7505114
- 4.Dominguez-Gomez G, et al. Ivermectin as an inhibitor of cancer stem-like cells: antitumor effects at clinically feasible concentrations. Cancer Chemotherapy and Pharmacology, 2020. View source
Educational information — not veterinary medical advice
Everything on this page is compiled from published peer-reviewed literature for educational and research purposes. It does not establish a veterinarian-client-patient relationship (VCPR) and is not a substitute for veterinary examination and diagnosis. Most compounds described here are investigational or used off-label and are not FDA-approved for these purposes in dogs. Extralabel drug use in animals requires a valid VCPR and the direct supervision of a licensed veterinarian under AMDUCA (21 U.S.C. §360b). Dosing figures are reported as they appear in the source literature and are not recommendations.