What are the long term effects of synthroid (thyroxine)? i've read about connections to cancer.

No relation: Hi. There is no causative relation between l-thyroxine (Synthroid) and cancer. None whatsoever. It just shows that just because something is found in print doesn't make it true.

No connection: with cancer . People with a history of thyroid cancer often take synthroid (thyroxine) for the rest of their lives. Synthroid (thyroxine) is T-4 a form of thyroid hormone!