Treating hypothyroidism
For canine hypothyroidism, thyroid hormone supplements are the best treatment. Levothyroxine 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 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.

Are there homeopathic remedies for hypothyroidism?
Some dogs benefit from homeopathic remedies for hypothyroid disease, which can include kelp and seaweeds because they are natural sources of iodine. Alfalfa, parsley, fennel, oats, the B Vitamins, Vitamin A—especially from cod liver oil—and Vitamin C can be helpful. If the immune system is sluggish, pets benefit from Omega fatty acids such as Super Pure Omega 3.