Hi there, Hypothyroidism is the most common side effect of radioactive iodine therapy. It occurs in almost 90-95% patients over long run. Since I don t know what was the primary indication for which radioactive iodine was given, I can t say whether you made the right choice. But in general for Grave s disease and Toxic nodule, radioactive iodine therapy is the first choice because of its efficacy and low toxicity. Only drawback is that patient almost always becomes hypothyroid and is needed to be put on thyroxine supplementation from outside. Hope I was able to help.