Can you tell me what to expect with someone who has undergone radioisotope thyroid therapy?

Hyperthyroid: Hi. Since you don't mention thyroid cancer, I'm going to assume the radioiodine therapy is to treat hyperthyroidism. If it's Graves' disease (the most common hyperthyroidism), the radioiodine is expected to make you hypothyroid; you then go on levothyroxine for life (easy & cheap - good therapy). If it's a toxic adenoma or toxic multinodular goiter, you may end back up with normal thyroid function

RAI post treatment: When treating Graves disease, sometimes the thyroid can get mildly tender and hyperthyroidism can get temporarily worse for about 1-2 weeks after RAI. A b-blocker helps, along with methimazole. But this is usually mild, temporary, and should not dissuade you. With thyroid cancer of other conditions, this is not an issue.