Online Facilitator
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    Hello – Ultimately, your doctor will need to help you sort this out, but there are a few possible reasons. If your thyroid wasn’t completely destroyed by the RAI (which is the goal with RAI these days, as they don’t want any thyroid tissue left behind), it’s possible for the tissue to regenerate, or for more tissue to be destroyed over time. But it could also be other factors – aging, weight gain/loss, changes in how you take the medication (time before breakfast, waiting 4 hours for iron/calcium supplements, etc.), or changes in the formula that affects your absorption (especially for generics if your pharmacy starts using a different manufacturer).