For canine hypothyroidism, thyroid hormone supplements are the best treatment. Levothyroxine (Soloxine) is the medication used, either once or twice a day. Medication is begun slowly and is adjusted until the proper blood level is achieved as measured by T3/T4 and TSH levels.
Once the medication is begun, improvement is seen in a few weeks. For example, many pets become more active and appear more alert within 1-2 weeks. Skin conditions resolve over a few months. Levothyroxine (Soloxine) is given for the rest of the pet's life. Because brands of Levothyroxine can be absorbed differently, the dose may change if the brand is changed.