GLP-1 agonists are specifically contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or MEN 2 syndrome—this is the black box warning. For common thyroid conditions like hypothyroidism (Hashimoto's) or hyperthyroidism (Graves'), GLP-1 agonists are generally considered safe, though you should tell your doctor. If you're on levothyroxine, be aware that GLP-1s may delay its absorption—take it on an empty stomach as usual, well separated from your injection.