Giving synthetic thyroid hormone externally raises levels of thyroid hormone in the blood and makes an existing overactive thyroid condition more severe.
Evidence from Studies
Supporting (2)
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Association between Over- and Under-Replacement with Thyroid Hormone and Incident Heart Failure
Giving people extra thyroid hormone pills can raise their thyroid hormone levels too high, which can hurt the heart — just like how too much of a good thing can become bad. This supports the idea that extra thyroid hormone can make hyperthyroidism worse.
Heterogenous biochemical expression of hormone activity in subclinical/overt hyperthyroidism and exogenous thyrotoxicosis
When people take extra thyroid hormone pills, their blood thyroid levels go up — even higher than in people whose own thyroid is overactive. This makes their hyperthyroid condition worse.
Contradicting (0)
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Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.