Medications Can Diminish Dog’s Sense of Smell

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Q: I’m training my dog Roger for search and rescue, which requires him to use his nose. I noticed while I was taking a particular medication that my sense of smell worsened. Can the same thing happen to dogs? If so, what drugs affect their sense of smell?

A: A dog’s nose has more than 300 million olfactory receptors that detect scent, while humans have only 400. Is it any wonder dogs are so good at scent work?

In humans, more than 70 drugs affect the sense of smell. So it shouldn’t be surprising that some medications can reduce scenting ability in dogs.

High doses of two commonly used steroid hormones, dexamethasone and prednisone, decrease dogs’ olfaction, or sense of smell. Metronidazole, often prescribed for diarrhea, can diminish dogs’ scenting ability, though olfaction returns to normal within 10 days of drug discontinuation.

Tobacco smoke decreases olfaction in rats and humans, though no research has been done on its effects on dogs.

Some drugs that impair the sense of smell in humans are suspected of affecting olfactory ability in dogs, although no research has been done on their effects on dogs. These include marijuana, the erectile dysfunction drug sildenafil, and the antihypertensive medications enalapril and captopril.

A single case report describes loss of the sense of smell in a human after the local anesthetic lidocaine was sprayed into the nostrils for nasal endoscopy. Another single human case report documents decreased olfaction after use of a ketamine nasal spray for pain. Both medications are used in dogs.

Research shows that some commonly used drugs do not diminish scenting ability in dogs. These include the antibiotic doxycycline, the anesthetics propofol and isoflurane, the pain reliever fentanyl, and naloxone, which is used to treat drug-detection dogs exposed to fentanyl and other opioids.

Fluoxetine, which relieves anxiety in dogs, actually improves olfaction in mice, though similar research has not been done in dogs.

Diet can affect the sense of smell, too. Research involving certified scenting dogs fed diets containing different amounts and kinds of fat found that neither a high- nor a low-fat diet affected scenting ability. However, a diet supplemented with corn oil produced mild olfactory improvement, while coconut oil decreased olfactory ability.

Some diseases also affect olfaction. If Roger gets sick and needs medication, let your veterinarian know about his scenting work, and ask when he'll be ready to return to duty.

Q: Dotty, my middle-aged calico cat, is losing the hair between her eyes and ears. She doesn’t scratch, and her coat is thick everywhere else. What is causing this?

A: Dotty may have feline pattern baldness, formally called preauricular alopecia. “Auricular” refers to the ear flap, and “alopecia” means hair loss, so this is thin or absent hair in front of the ears.

The condition is common in cats. Other than having sparse hair between the eyes and ears, affected cats look normal. They don’t scratch or rub, the skin isn’t red or bumpy, and the hair doesn’t fall out easily when tugged.

If Dotty does develop any of these clinical signs, make an appointment with her veterinarian. If not, you can wait until her next wellness exam to ask her veterinarian about her sparse facial hair.

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