When your dog doesn't produce enough thyroxine naturally to maintain a normal metabolic rate, your vet may prescribe tablets to assist a sluggish thyroid. If your dog's an "easy keeper" -- or tends to gain weight even when fed the minimum amount of food recommended for his size and breed -- he could have a thyroid condition requiring medication. Your dog likely will need to stay on this medication for life. Your vet will help you weigh the benefits and advise you of the side effects.
Look for Symptoms
In addition to gaining weight easily, a dog suffering from hypothyroidism tends to be low energy and spends much of his time sleeping. As the condition advances, a dog's coat becomes dull and hair begins to thin, especially on the tail and rear legs. Laboradors and golden retrievers are two breeds most prone to hypothyroidism, but the disorder is commonly seen in cocker spaniels, dachshunds, Dobermans, boxers and greyhounds.
Look for Side Effects
Levothyroxine sodium is commonly prescribed for canine hypothyroidism. Keep track of side effects as they can let your vet know whether to increase or lower your dog's dosage. If the dosage is too high, it may produce side effects that include diarrhea, agitation and frequent trips to the water bowl. If the dosage is too low, the condition will continue to progress. Your vet will do a blood screening 30 days after beginning the medication to confirm a correct dosage.