My kitty was just diagnosed with hyperthyroidism and I wanted to pass on some helpful information :

Comparison of Treatments for Hyperthyroidism in Cats

Methimazole (pill form or dermal)
(Can purchase on 1800petmeds.com for .45 cents per pill or around $15 a month)

Advantages
Medication readily available
Inexpensive in short-term
No anesthesia or surgery
No hospitalization or special facilities required
Treatment is reversible, if needed
Development of hypothyroidism very rare
Preferred in cats with kidney failure or other serious disease
Used prior to radiation or surgery to stabilize cat Not a cure; the adenoma will continue to grow

Disadvantages
Lifelong therapy necessary
Medication may need to be given more than once daily
May be difficult to give medication
Medication occasionally has side effects some cats cannot tolerate
Periodic blood work required

Surgery
Advantages
Cures the condition unless all of the abnormal tissue is not removed
Approximately the same cost as several years of methimazole
Short hospitalization
No need for daily medication Requires anesthesia
Cat must be a good surgical candidate

Disadvantages
Post-operative complications can occur to parathyroid gland or nerves in the area
Could rarely cause hypothyroidism
Not possible if thyroid tissue is located within the chest
May need to be repeated


Radioactive Iodine Treatment
Advantages
No anesthesia, sedation, or surgery
All abnormal tissue is treated
No need for daily medication
Does not destroy healthy tissue or other organs
Normal thyroid function returns within a month
Preferred if malignancy present, or thyroid tissue located within the chest

Disadvantages
Availability limited
Most expensive alternative: over $1,000
Specialized facility required
Hospitalization and quarantine required
Treating other diseases during initial days following treatment is not possible
In rare cases may need to be repeated
Could rarely cause hypothyroidism