Another paper asking deep questions about adding T3. It particularly mentions and discusses bone issues. Well worth a read if you are interested. Much of the paper is easier to read than the Abstract below! And free, open access to full paper.
Perhaps surprisingly, they equated 20 mcg of Liothyronine to 50 mcg levothyroxine.
Peripheral markers of thyroid function: the effect of T4 monotherapy vs T4/T3 combination therapy in hypothyroid subjects in a randomized crossover study
Background: A recent randomized controlled trial suggests that hypothyroid subjects may
find levothyroxine (L-T4) and levotriiodothyronine combination therapy to be superior to
L-T4 monotherapy in terms of quality of life, suggesting that the brain registered increased T3 availability during the combination therapy.
Hypothesis: Peripheral tissue might also be stimulated during T4/T3 combination therapy
compared with T4 monotherapy.
Methods: Serum levels of sex hormone-binding globulin (SHBG), pro-collagen-1-N-terminal
peptide (PINP), and N-terminal pro-brain natriuretic peptide (NT-proBNP) (representing
hepatocyte, osteoblast, and cardiomyocyte stimulation respectively) were measured in
26 hypothyroid subjects in a double-blind, randomized, crossover trial, which compared the
replacement therapy with T4/T3 in combination (50 mg T4 was substituted with 20 mg T3) to T4 alone (once daily regimens). This was performed to obtain unaltered serum TSH levels during the trial and between the two treatment groups. Blood sampling was performed 24 h after the last intake of thyroid hormone medication.
Results: TSH remained unaltered between the groups ((median) 0.83 vs 1.18 mU/l in T4/T3
combination and T4 monotherapy respectively; PZ0.534). SHBG increased from (median)
75 nmol/l at baseline to 83 nmol/l in the T4/T3 group (PZ0.015) but remained unaltered in
the T4 group (67 nmol/l); thus, it was higher in the T4/T3 vs T4 group (PZ0.041). PINP levels were higher in the T4/T3 therapy (48 vs 40 mg/l (P!0.001)). NT-proBNP did not differ between the groups.
Conclusions: T4/T3 combination therapy in hypothyroidism seems to have more metabolic
effects than the T4 monotherapy.