What Are the Side Effects of Melatonin Treatment in Canines?

Melatonin (brand name Melatonex) is a human medication prescribed for dogs that suffer from seizure disorders like epilepsy or as a sedative for dogs suffering from phobias. This is an off-label use of the drug. Side effects are common.

  1. Most Common Effects

    • According to veterinarian Dr. Nicholas Dodman, the most common side effect of melatonin in dogs is drowsiness. The dog also may be slower to react to any given stimulation.

    Unusual Side Effects

    • According to Canine Epilepsy Guardian Angels, call the vet if a dog on melatonin has coordination problems, walks into furniture as though blind or urinates in the house. These problems could be caused by a slight overdose.

    Irregular Cycles

    • Dodman also notes that Melatonex can cause unspayed female dogs to have irregular heat cycles.

    Speculation

    • According to the American Journal of Respiratory and Critical Care Medicine, dogs on melatonin breathed easier because melatonin relaxed the bronchial tubes in the dogs' lungs. The use of melatonin may help dogs with asthma or other breathing problems.

    Warning

    • Symptoms of an allergy to melatonin or a lethal overdose include seizures, vomiting, diarrhea, coordination problems and uncontrollable quivering. The dog should be taken immediately to the vet.