Breed profile
Collie & MDR1
70%
carry the mutation
Last verified June 16, 2026
The Collie is the breed where the MDR1 (ABCB1) mutation was first recognised, and it carries the highest published frequency on the WSU table. WSU notes that approximately three of every four Collies in the United States carry at least one copy of the mutant gene. Because the frequency is so high, many Collie owners and breeders test as a matter of routine before any anaesthesia, mange treatment, or chemotherapy. A high population frequency does not tell you your individual dog's genotype — a normal/normal Collie is not at increased risk from these drugs — so a DNA test is the only way to know.
MDR1 status is one factor among many in your dog's health
A high breed frequency is not a diagnosis, and a positive result is not a crisis. The mutation affects a specific, knowable list of drugs at specific doses. Most affected dogs live entirely normal lives once their owners and vets know the list.
Drugs to flag for a Collie
These are among the most commonly encountered MDR1-relevant drugs. The full list and every dose-tier rule lives in the drug checker below — and on each drug's own page.
- LoperamideClass A · Avoid
Avoid in all dogs with the MDR1 mutation
- IvermectinDose-tier dependent
Safe at heartworm-prevention dose · dangerous at high (mange) doses
- AcepromazineClass B · Caution
Use a reduced dose — affected dogs are more sensitive
- ButorphanolClass B · Caution
Use a reduced dose — affected dogs are more sensitive
Check any drug for your Collie
The checker is pre-set to the Collie. Pick a drug to get the cite-pinned verdict.
Which drug for your Collie?
Search by drug name, brand (e.g. Imodium, Heartgard), or class.
This is general information, not veterinary advice for your dog. It does not diagnose or prescribe. Always discuss any medication decision with your veterinarian before acting — they know your dog's full picture, including its MDR1 status if it has been tested. See our disclaimer and how we research.
What a Collie's test result will say
- Mutant/mutant — Both copies of the gene are mutated. This is the highest-sensitivity genotype. WSU describes affected drugs as causing toxicity in homozygous dogs; reduced doses or avoidance apply most strongly here.
- Mutant/normal — One copy is mutated and one is normal. This is an intermediate-sensitivity genotype. WSU advises that heterozygous dogs can also experience toxicity and should receive reduced doses of affected drugs.
- Normal/normal — Both copies are normal. A normal/normal dog does not carry the MDR1 mutation and is not at increased risk from these drugs at normal doses. A DNA test is the only way to confirm a dog is normal/normal.