A dog that eats a human muscle relaxer can develop serious, potentially life-threatening symptoms within 30 minutes to a few hours. The severity depends on which medication was swallowed, how much, and how big your dog is. Some muscle relaxants, particularly baclofen, have an extremely narrow safety margin in dogs, and fatalities have been reported at surprisingly low doses. This is a veterinary emergency.
What to Do Right Now
Call your veterinarian or the nearest emergency veterinary clinic immediately. If you can’t reach one, call the ASPCA Poison Control Hotline at 888-426-4435 or the Pet Poison Helpline at 855-764-7661. Have the following information ready: the brand name or active ingredient on the pill bottle, how many pills are missing, when your dog ate them, and your dog’s approximate weight. Do not try to induce vomiting on your own unless poison control or a vet specifically tells you it’s safe to do so.
Symptoms to Watch For
Signs of muscle relaxant poisoning can appear as quickly as 30 minutes after ingestion, though extended-release formulations may take longer. The most common symptoms include:
- Behavioral changes: agitation, unusual vocalization (growling, whining), or the opposite: extreme drowsiness and dull awareness
- Loss of coordination: stumbling, wobbling, or inability to walk straight
- Tremors or shaking
- Drooling and vomiting
- Heart rate changes: either abnormally fast or abnormally slow
- Dangerously low blood pressure or body temperature
- Seizures or coma in severe cases
In one documented case, a 4-year-old Rat Terrier that ate cyclobenzaprine (sold as Flexeril) arrived at the emergency room with a heart rate of 180 beats per minute, panting, trembling, and growling, which was completely out of character. A 5-month-old mixed-breed puppy that swallowed the same drug lost its gag reflex and could barely coordinate its legs. Both dogs also had elevated blood pressure.
Which Muscle Relaxants Are Most Dangerous
Not all muscle relaxants carry the same risk. The type your dog ate matters significantly.
Baclofen
Baclofen is the most dangerous muscle relaxant for dogs. It has such a narrow safety margin that it’s not even recommended for veterinary use. Doses as low as 1.3 mg/kg of body weight have triggered vomiting, depression, and vocalization in dogs. Deaths have been reported at doses as low as 2.3 mg/kg. To put that in perspective, a single 10 mg baclofen tablet could be lethal for a small dog. The primary concern with baclofen poisoning is a severe drop in blood pressure that can lead to kidney damage.
Cyclobenzaprine (Flexeril)
Cyclobenzaprine affects the brain, targeting the same chemical messenger systems that regulate mood, alertness, and heart function. In dogs, it tends to cause a fast heart rate, high blood pressure, agitation, tremors, and altered mental state. One complicating factor is that cyclobenzaprine recirculates through the liver and gut, which means it can keep re-entering the bloodstream for hours after ingestion. This often requires repeated treatment to fully clear the drug.
Methocarbamol (Robaxin)
Methocarbamol is actually used in veterinary medicine, so it has a wider safety margin than baclofen or cyclobenzaprine. An overdose typically causes heavy sedation, drooling, weakness, and poor coordination. It’s still a serious situation that needs veterinary attention, but it’s generally less life-threatening than the other two if the amount ingested is modest.
How the Vet Will Treat It
If your dog ate the pill recently and isn’t yet showing severe symptoms, the vet will likely induce vomiting to get as much of the drug out as possible. They may follow this with activated charcoal, a substance that binds to the medication in the gut and prevents the body from absorbing more. Activated charcoal works best within the first one to two hours after ingestion.
For cyclobenzaprine specifically, because the drug keeps recirculating through the body, your dog may receive additional doses of activated charcoal at six- to eight-hour intervals. Dogs that ate baclofen may be treated with a special fat-based solution given through an IV, which has been reported to successfully counteract baclofen poisoning in some cases.
Beyond decontamination, treatment is largely supportive. Your dog will likely receive IV fluids to maintain blood pressure, replace fluids lost from vomiting, and help flush the drug from the kidneys. The vet will monitor heart rate, blood pressure, kidney function, and breathing throughout. Dogs with severe poisoning may need respiratory support if their nervous system becomes too depressed to breathe normally.
Recovery and What to Expect
Recovery depends heavily on the type and amount of medication, how quickly treatment began, and your dog’s size. Small dogs are at far greater risk simply because the same pill represents a much larger dose relative to their body weight.
Dogs that receive prompt treatment for methocarbamol or moderate cyclobenzaprine ingestion generally recover well. Hospitalization for monitoring and IV fluids typically lasts 12 to 48 hours, depending on the severity of symptoms and whether the drug continues to recirculate. Baclofen poisoning tends to require longer and more intensive care because of the risk of blood pressure collapse and kidney damage.
The single most important factor in your dog’s outcome is how quickly you get veterinary help. Dogs treated within the first hour or two, before the drug is fully absorbed, have a significantly better prognosis than those who arrive after symptoms have progressed to seizures, coma, or dangerously low blood pressure.