Thyroid UK

Levothyroxine: from sheep thyroid injections to synthetic formulations

Here we go again!!

I've just read an article and one of the phrases struck home:

“Levothyroxine is the most perfect hormone replacement that has yet been devised for endocrine conditions, but there are undoubtedly people who fall outside the current treatment model. Animal-derived products that contain T4 and T3 are not physiological and are not the answer in the longer term, but we do need to find ways to ensure that all our patients with hypothyroidism feel the full benefits of replacement therapy.”

Another phrase:

The ETA concluded that there was insufficient evidence to show that combination treatment is more effective than monotherapy. Having considered the factors that have been linked to persistent symptoms in the presence of adequate biochemical control of hypothyroidism, the ETA recommended that endocrinologists should reassure patients about their condition and support them in coming to terms with a chronic disease requiring life-long medication.

The T4/T3 ratio stated in the article is:-

When combination treatment is considered appropriate, the ETA suggests that treatment should be started in a L-T4/L-T3 dose ratio between 13:1 and 20:1 by weight, and that L-T3 should be divided in two doses (one before breakfast and the largest one at bedtime).

whereas another study below recommends (page 80)

Subsequent research by the US National Institutes of Health

(NIH) found the therapeutic equivalence was 3:1. Thus, most of the subjects were under treated with the T3/T4 combination. In light of the NIH finding, the conclusion that T3 therapy is never needed is invalid.

In the article no mention is made about the possibility of the DIO2 (deiodinase 2 gene). preventing the uptake of T3. Nothing about thyroid hormone resistance (they may not think that's possible). We already know that the statement is by a doctor who would rather diagnose a 'Somatization Disorder' than attempt to give the sick patient an alternative when bloods show the 'exquisite' TSH is in range.

A sensible, responsible response in the BMJ

3 Replies

I'm no maths genius but how does 20% = 14:1? These are in two paragraphs with a quote in between. I sometimes feel like Alice.


NDT isn't physiological but synthetic levothyroxine therapy is? If only these "experts" would disappear in a puff of their own logic!


One of the problems with much of the written material is that there are assumptions, not always obvious, which need to be understood.

The classic one is that so many guidelines and reviews are actually strictly limited to "simple" hypothyroidism. Throw in any degree of hypopituitary, or resistance to thyroid hormone, or autoimmune disorder, or ...., and they are inapplicable. But all too many readers (e.g. GPs) fail to understand that limitation. (They might still not be valid, but that is another issue.)


You may also like...