Codeine Side Effects in Dogs

By Susan Paretts

Codeine is an opioid narcotic that must be prescribed by your vet to treat pain, diarrhea or to suppress a dog's cough. Give this drug to your dog only as directed by your vet because it is a controlled substance, usually given orally or by injection. Side effects of codeine in dogs are generally mild if given in the correct dosage.

Codeine for Dogs

Codeine is derived from the opium poppy plant and works similarly to morphine.

  • The medication works by mimicking the brain's natural pain-reducing chemicals to help relieve your pup's discomfort.
  • While codeine isn't approved for use in dogs by the U.S. Food and Drug Administration, your vet may prescribe it for your pooch off-label.
  • She may prescribe it to treat pain due to joint issues, surgical pain, back issues and muscle pain.
  • Because codeine has a constipating effect, it also may be prescribed to treat diarrhea in dogs.
  • It also has cough-suppressant properties and your vet might prescribe it to treat your pup's cough.

Codeine Side Effects

The primary side effects of codeine are sedation and lethargy in dogs, especially when first taking this medication. These effects will decrease over time as your pup continues to take the medicine and his body adjusts to it.

  • Your dog may experience constipation, vomiting and a decrease in his appetite after taking codeine.
  • In some cases, you may notice labored breathing as a side effect of codeine.
  • Codeine may cause urine retention in your dog.
  • Your dog's heartbeat may slow after taking this medication.
  • Dogs with seizure disorders may experience convulsions after taking this drug.

If you notice any of these side effects, consult with your vet to determine if your dog's codeine dosage should be adjusted.

Possible Allergic Reactions and Precautions

Allergic reactions to opioid medications, including codeine, aren't common in dogs, according to "Anesthesia and Analgesia in Laboratory Animals." If your dog is allergic to codeine, he may experience a variety of symptoms, including restlessness, vomiting, diarrhea, low blood pressure or a fast heartbeat. If you notice any of these or other symptoms, bring your dog to the vet. He may be experiencing anaphylaxis, a type of severe allergic reaction, which your vet can treat with medications such as epinephrine to counteract the effects of codeine in your pup's body.

Discuss using codeine with your vet if he is elderly, debilitated or suffers from kidney, liver, respiratory, adrenal gland or thyroid disease. This drug may not be safe for him.

Drugs That Interact With Codeine

Codeine may react negatively with a number of drugs, so alert your vet if your pooch is taking any other medications before giving it to him.

  • Opiate antagonists such as naloxone can negate the effects of codeine.
  • Central nervous system depressants, including benzodiazepines and barbiturates, such as phenobarbital, may increase the depressant effects of codeine.
  • Don't use topical insecticides such as Amitraz on your dog when he's taking codeine, as the drugs may interact negatively.
  • Other medications, including monoamine oxidase inhibitors such as selegiline, should not be given with codeine. Note that aged cheese reacts negatively with codeine in a similar way to monoamine oxidase inhibitors.
  • Some antibiotic, anticholinergic and steroid medications also may react badly with codeine.