- Apr 2018
There was a boy who was born with congenital hypothyroidism and was raised on traditional T3 (Cytomel). He was never treated with a T4-containing medicine, and so essentially never had a molecule of T4 in his body. By age 26 he had developed normally with no problems.
This is precisely the type of information I was looking for. Wikipedia implied T4 should be taken with long-term T3, but the reasoning was poorly explained. However, I'd like a more official source for this case report.
This case would also express no rT3 (reverse-T3). Thus, it appears that neither T4 nor rT3 serve any vital functions.