If you are hypothyroid, you might find lipoic acid interferes making T3 (active thyroid hormone) from T4 (synthroid, levoxyl) and you could become more hypothyroid. This happened to me, I believe; although I won't know for sure until my next set of bloods, drawn after I stopped the lipoic acid.

Effect of alpha-lipoic acid on the peripheral conversion of thyroxine to triiodothyronine and on serum lipid-, protein- and glucose levels.
Segermann J, Hotze A, Ulrich H, Rao GS.

Institute of Clinical Biochemistry, University of Bonn, Fed. Rep. of Germany.

The influence of alpha-lipoic acid (LA, thioctic acid, CAS 62-46-4) on thyroid hormone metabolism and serum lipid-, protein- and glucose levels was investigated. In the first setup of experiments administration of LA together with thyroxine (T4) for 9 days suppressed the T4 induced increase of T3 generation by 56%. This suppression was similar to that affected by 6-propylthiouracil (54%). LA or T4 alone did not affect the cholesterol level, but together they led to a reduction. LA decreased the triglyceride level by 45%; the decrease induced by T4 or LA plus T4 was not significant. Total protein and albumin levels decreased by LA plus T4 treatment when compared to the LA control. The slight increase in glucose level by LA or T4 alone was not observed when they were administered together. In the second setup of experiments the administration of T4 for 22 days increased the serum T3 level 3-fold. When LA was combined with T4 and the treatment continued, the T3 production decreased by 22%. T4 reduced cholesterol level by 30%, and LA plus T4 further reduced it by 47%. The triglycerides were not affected. A moderate decrease in total protein was observed after treatment with T4 plus LA; T4 and LA plus T4 decreased the albumin level. The decrease in serum glucose by T4 recovers by LA treatment. These results demonstrate that LA interferes with the production of T3 from T4 when it is co-administered with T4. The elevated level of T3, after T4 administration, is reduced by treatment with LA.(ABSTRACT TRUNCATED AT 250 WORDS)

PMID: 1815532 [PubMed - indexed for MEDLINE]