The research showed that taking vitamin C along with levothyroxine reduced TSH levels substantially, by as much as 27%. Taking the levothyroxine along with 1 gram of vitamin C mixed with water over a period of six weeks was able to help the majority of patients achieve their TSH target level. The researchers concluded that vitamin C can enhance oral absorption of levothyroxine, and taking vitamin C along with levothyroxine medications should be considered in patients with difficulties in the absorption of levothyroxine.
So, if you're not able to get your thyroid problem under control, talk to your doctor about the possibility of using supplemental vitamin C along with your thyroid medication.
Source: S. Licht et. al. ďDifficulties In The Absorption Of Levothyroxine: Improvement Using Vitamin CĒ Abstracts of the American Thyroid Association October 2008 Meeting, Online