The current Wiki article on levothyroxine has many references, including:
15 Midgley JE, Larisch R, Dietrich JW, Hoermann R (August 2015). "Variation in the Biochemical Response to L-Thyroxine Therapy and Relationship with Peripheral Thyroid Hormone Conversion". Endocr Connect. 4: pii: EC–15–0056. doi:10.1530/EC-15-0056. PMC 4557078 Freely accessible. PMID 26335522.
en.wikipedia.org/wiki/Levot...
Good to see someone has linked to diogenes, et al, research papers.