How fast will you lose thyroid hormone from your blood if you stop taking synthroid/levoxyl?

January 11, 2008 6:40 PM

How quickly will your TSH lower if you stop taking daily thyroid hormone pills such as Synthroid/Levoxyl?

I know quite a bit about Hashimoto's Thyroiditis. However, while I know it takes a long time for typical synthetic thyroid hormones like Synthroid and Levoxyl to get circulating in your blood at the desired level, depending how much you have to boost the level (as in various states of hypothyroidism) - suppose you want to lower the level? A few days ago, it was determined that my friend's TSH was now for the first time too low and outside the normal TSH range (down to about .075) and so he was feeling pretty wiggy. The doc told him to stop taking the dose he was on altogether for about 3 days, then start taking the next lowest level.

It was estimated he ought to start feeling quite a bit better in about a month, if his symptoms were indeed brought on as a result of too much thyroid hormone. ?

posted by bitterkitten to Health & Fitness (5 answers total)

I've been told that if I've been consistent about taking my Synthroid correctly, my levels should stay OK for about a week.
posted by Cricket at 7:24 PM on January 11, 2008

I've been on levoxyl for about 15 years (a moderate dose initially for Hashimoto's, then a larger, full replacement dose after thyroidectomy for cancer). In my experience, whenever I've adjusted my dosage downward, it takes at least a week to start feeling the shift and about a month or so to stabilize at the new dose.
posted by scody at 7:30 PM on January 11, 2008

If your friend were my patient, I'd have him lay off the medicine for about a week (anywhere from 3-14 days would be acceptable), then start the lower dose. (I've been a practicing internist for 12 years.)
posted by neuron at 9:56 PM on January 11, 2008

This is confusing. T(hyroid)S(timulating)H(ormone) is what your pituitary makes to tell your thyroid to make T4 (which becomes T3, which is the more active form). When T4 is high, TSH lowers very quickly. Your friend had LOW TSH because his T4 was too high, because he was taking too much synthetic T4. Now that he's not taking it, his TSH will RISE. Depending on what's wrong with him/her that could change a bit; the wiki article on TSH covers it.

From here

"Levothyroxine is nearly totally bound to serum proteins and has an elimination half-life of 6 to 7 days in the euthyroid subject. Half-life is shortened in hyperthyroidism and prolonged in hypothyroidism and in pregnancy. Deiodination of levothyroxine (T4) to 1-triiodothyronine (T3) occurs in various tissues, particularly liver and kidney. T3 is approximately 4 times as potent as T4 on a weight basis."

TSH itself is a peptide, and has a half-life of about an hour, so it will very quickly reflect what the brain thinks about the level of circulating T3/T4. T3/T4 will decay off slowly; how long it takes to get to normal will depend on how high he was. If he was double normal, then it will take a week or so.
posted by a robot made out of meat at 6:57 AM on January 12, 2008

Response by poster: Ooops. Yes, you are correct. I totally screwed that up, re TSH - indeed it should be, how fast will it rise. Unfortunately I cannot correct it, I don't think? Although more importantly, it was really about how fast he will feel better due to having less T4.

Thanks for the info though, that is helpful!
posted by bitterkitten at 6:02 PM on January 14, 2008