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Antidepressents interfering with FT3 blood results - just want to inform others

Since being Hashi/hypo I have had phases on and off AD's. Actually I was taking AD's long before being diagnosed. So what's new!!!

However over the years I have noted that when I am not taking AD's my FT3 levels are much lower. Now I put this down to a slight over conversion issue. Caused by the SSRI. That's a guess. Naturally.

Just thought I'd throw this out there.

So if you are on SSRI's and come off them and then see your FT3 blood levels drop.......don't be surprised.

I know SSRI's affect a lot of things and work in a very complex way. Not even the doctors truly fully understand I believe. I haven't mentioned this to my GP because of course I'd be deemed MAD AS A BOX OF FROGS!!!!😀

7 Replies

This effect has been known for a while. Here's an oldish reference:

Scand J Clin Lab Invest. 1980;40(8):767-74.

Effect of anticonvulsant and antidepressant drugs on iodothyronines in serum.

Liewendahl K, Helenius T, Majuri H, Ebeling P, Ahlfors UG.


Serum iodothyronine concentrations were measured in patients on long-term therapy with one or two anticonvulsant drugs. Diphenylhydantoin (DPH) and carbamazepine (CBZ) reduced the serum levels of thyroxine (T4) free T4 index, reverse triiodothyronine (rT3) and 3,3'-diiodothyronine (3,3'-T2), whereas the depressant effect on the serum levels of triiodothyronine (T3) and free T3 index was small but statistically significant. In patients administered DPH and phenobarbital (PB) or CBZ and primidone (PD) the serum iodothyronine levels were also depressed, except for normal T3 and free T3 index. Patients receiving only PB or PD had normal serum levels of total and free thyroid hormones, but decreased concentrations of rT3 and 3,3'-T2. Only supratherapeutic concentrations of DPH and CBZ added in vitro to control sera significantly reduced the number of T4 and T3-binding sites, as reflected in increased T4 and T3 uptake test results. This indicates that the DPH and CBZ-induced decrease in thyroid hormone concentrations in vivo is not due to a displacement of thyroid hormones from their binding sites on serum proteins. The antidepressant drugs amitriptyline and mianserin had no effect on the thyroid hormone levels in serum.


Could you post a link to this please? I want to show gp


(As I'm deemed mad as a box of frogs!!!!)


There is an even nicer long review you can access direct which is more modern:

Journal of Thyroid Research

Volume 2012 (2012), Article ID 590648, 8 pages

Review Article

The Link between Thyroid Function and Depression

Mirella P. Hage and Sami T. Azar

1 like

Interesting - I've been very unwell indeed since being on sertaline. It is the only one where its known it affects Tsh abd t4 levels but I belive it affected my ability to convert t4 to t3. Of course I've never had t3 done, but my muscles have been severely affected. 5 weeks off it and I'm suddenly starting to feel better.....


Suspect it's more likely that you've been over converting than under converting. Your ft3 could have been too high. That's what happened to me on Seroxat.x


My doctor prescribed sertaline for my perimenopausal mood swings but I was not keen on starting a drug with a long list of possible side effects so I consulted my kinesiologist who advised upping my fish oils to 4g and lo and behold I am feeling much much better in my mind though my body is still catching up (but maybe because some other neurotransmitters than serotonin tested out of kilter so we will try to treat them with GLA and Vit B complex).

You might want to check this link anyway..


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