The MDR1 Gene:

What Every Aussie Owner Needs to Know

One in two Australian Shepherds carries a genetic mutation that can make common medications deadly. Here's everything you need to know and what to do about it.

Of Aussies carry MDR1

Test Needed

Conditions Embark Tests For

50%

250+

1x

Important: Always inform your veterinarian: If your Aussie has tested MDR1 positive, share their results with every veterinarian who treats them; including emergency vets, groomers who use sedation, and boarding facilities. Keep a copy of their test results and the drug sensitivity list in their records at all times.

What Is the MDR1 Gene?

MDR1 stands for Multi-Drug Resistance 1 — a gene that produces a protein called P-glycoprotein. In healthy dogs this protein acts as a pump, preventing certain drugs from crossing into the brain and clearing them from the body efficiently.

In dogs with the MDR1 mutation, this pump is either partially or fully non-functional. When affected dogs are given certain medications, those drugs enter the brain, fail to be cleared, and build up to toxic levels — causing serious neurological reactions that can include tremors, seizures, disorientation, and in severe cases, death.

The MDR1 gene is also known as ABCB1, and you may see either name used by your veterinarian or on DNA test results. They refer to the same mutation.

Why Aussies Are Especially at Risk

The MDR1 mutation occurs across a number of herding breeds, but Australian Shepherds are among the most commonly affected. Approximately 50% of Australian Shepherds carry at least one copy of the mutation — meaning if you have an Aussie, there is a one-in-two chance they are affected to some degree.

This is not a rare edge case. It is one of the most clinically significant genetic considerations for the breed, and every Aussie owner — whether their dog is a rescue, a purchased puppy, or an Aussie mix — should know their dog's MDR1 status."

Info box: "Also affects Aussie mixes — If your dog is an Australian Shepherd mix, they can still carry the MDR1 mutation. ASF recommends testing any dog with known or suspected Aussie heritage, particularly before any procedure involving sedation or the medications listed below.

Understanding Your Dog's Test Results

DNA tests for MDR1 return one of three results. Understanding what each means will help you communicate your dog's needs clearly to their veterinary team.

Normal / Clear - No copies of the mutation. Your dog can receive all medications normally. No restrictions needed.
Carrier (1 copy) - One copy of the mutation. Your dog has some drug sensitivity. Caution and veterinary guidance required for listed medications.
Affected (2 copies) - Two copies of the mutation. Highest sensitivity. The listed medications should be avoided or significantly dose-adjusted under specialist guidance.

The test only needs to be done once in your dog's lifetime. Results do not change. Once you have them, keep a copy on file and share them with every vet who treats your dog.

Medications to Use With Caution or Avoid

1. Tell every vet who treats your dog - Give a copy of their test results and the drug sensitivity list to your primary vet, any specialists, emergency vets, and even groomers who use sedation. Ask them to note it prominently in your dog's file.

2. Keep documentation on hand - Store a photo of the test results and drug list on your phone. In an emergency where your dog needs immediate treatment, you may not have time to explain - having it ready can be lifesaving.

3. Check all medications before administering - Before giving any new medication - including over-the-counter products like Imodium - check whether it appears on the MDR1 sensitivity list. When in doubt, call your vet before giving it.

4. Ask about alternatives before any procedure - If your dog needs surgery or sedation, discuss MDR1-safe anesthetic protocols with your vet in advance. Safer alternatives exist for almost every affected medication - your vet just needs to know to use them.

5. Consider a medical alert tag - The Washington State University Veterinary Clinical Pharmacology Lab (VCPL) offers a medic-alert style collar tag for MDR1-affected dogs. This can be helpful if your dog is ever treated without you present.

FAQs

My vet has never mentioned MDR1 - should I be worried?
- Not worried, but proactive. MDR1 awareness varies significantly among veterinary practices, and many vets who don't specialize in herding breeds may not routinely test for it or discuss it. It's worth raising with your vet at your next visit and requesting a DNA test if your dog hasn't been tested. Simply knowing the status puts you and your vet in a position to make safe decisions.
Can my dog live a completely normal life with the MDR1 mutation
- Absolutely. The MDR1 mutation only becomes a problem when an affected dog is given one of the sensitive medications. With knowledge of their status, your dog can live a full, healthy life - you and your vet simply need to make informed medication choices. Many Aussies go their entire lives without ever encountering a problematic medication.
My dog is an Aussie mix - do they need to be tested?
- Yes, we recommend testing any dog with known or suspected Australian Shepherd heritage. The mutation can be passed on through mixed breeding, and there's no way to know without testing. Given how common the mutation is in Aussies, it's a sensible precaution for any Aussie mix.
How much does MDR1 testing cost?
- A standalone MDR1 test through your vet typically costs $40–$70. A comprehensive DNA test like Embark - which includes MDR1 along with 250+ other health conditions, breed breakdown, and trait information - is a more complete option and provides a much richer picture of your dog's health profile.
Does my dog need to be retested over their lifetime?
- No. The MDR1 mutation is genetic - it doesn't change over time. The test only needs to be done once, and the results are valid for your dog's entire life. Keep a copy of the results somewhere accessible.
Is MDR1 the only genetic concern I should know about for my Aussie?
- MDR1 is one of the most important, but Aussies have a few other genetic health considerations worth knowing about - including hereditary eye conditions (CEA, PRA), epilepsy, and hip dysplasia. A comprehensive DNA test like Embark covers many of these alongside MDR1, giving you a complete genetic health picture in one test. Visit our Genes & Health page for more information on Aussie genetic health.

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