How long does it take for levothyroxine to reduce TSH?

[Yogamat123]

Hi, I was diagnosed with sub clinical hypothyroidism a few years ago. I later had antibodies tested too and they were in the 100’s. I took levothyroxine through my last pregnancy but my GP suggested stopping it and just monitoring blood test results for a while. Following a blood test result where my TSH went just above the upper range, a different GP suggested I re start Levothyroxine which has been great, and I’m feeling a lot better. However, my TSH is slow to decrease. Started at 4.26 when I first restarted Levo in July last year, down to 3.29 in the November and now 3.12 as of last week. The serum free thyroxine has remained in the lower range of normal. After each result I’ve requested to have a levo increase which the GP has agreed to. I have a telephone appointment tomorrow so will request another increase. I’m currently taking 75mcg. I find a similar pattern each increase: I feel lots better after a week or two, then after around 6 weeks I start to feel more tired and the brain fog kicks in again. I’m hoping for a sympathetic GP tomorrow who allows me to increase the dose again! I just wanted to check that it’s normal for it to be so slow for the TSH to decrease and if it’s fair to keep increasing the medication until it reaches the lower end of normal. Thank you 🙏

[SeasideSusie Remembering]

Yogamat123

However, my TSH is slow to decrease. Started at 4.26 when I first restarted Levo in July last year, down to 3.29 in the November and now 3.12 as of last week. The serum free thyroxine has remained in the lower range of normal. After each result I’ve requested to have a levo increase which the GP has agreed to.

Retesting should be done 6-8 weeks after any dose change.

It sounds like you are undermedicated and your GP should stick to the titration protocol.

I feel lots better after a week or two, then after around 6 weeks I start to feel more tired and the brain fog kicks in again.

This is typical, return of symptoms means you are ready for a dose increase and the timing is about right.

Is TSH all that is being tested? This doesn't give a full picture. TSH is not a thyroid hormone, it's a signal from the pituitary to tell the thyroid to produce more hormone when it detects there's not enough. The thyroid hormones are FT4 and FT3 and it's essential that these are also tested, although most GPs don't test them. If FT3 and, particularly, FT3 are low in range then we are undermedicated.

Dr Toft, past president of the British Thyroid Association and leading endocrinologist, states in Pulse Magazine (the professional magazine for doctors):

"The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l. In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance. But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l. This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l).*"

*He recently confirmed, during a public meeting, that this applies to Free T3 as well as Total T3.

You can obtain a copy of the article by emailing Dionne at

[e-mail]

print it and highlight question 6 to show your doctor and ask for full thyroid testing - TSH, FT4 and FT3.

[SlowDragon Administrator]

The aim of levothyroxine is to increase dose upwards in 25mcg steps until TSH is always under 2

When adequately treated, TSH will often be well under one. Most important results are ALWAYS Ft3 followed by Ft4. When adequately treated Ft4 is usually in top third of range and Ft3 at least 60% through range (regardless of how low TSH is)

Extremely important to have optimal vitamin levels too as this helps reduce symptoms and improve how levothyroxine works

Ask GP to test vitamin D, folate, ferritin and B12 levels

What vitamin supplements are you currently taking ?

TSH should be under 2 as an absolute maximum when on levothyroxine

gponline.com/endocrinology-...

Replacement therapy with levothyroxine should be initiated in all patients to achieve a TSH level of 0.5-2.0pmol/L.

[SlowDragon Administrator]

guidelines on dose levothyroxine by weight

Even if we don’t start on full replacement dose, most people need to increase levothyroxine dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until on, or near full replacement dose

NICE guidelines on full replacement dose

nice.org.uk/guidance/ng145/...

1.3.6

Consider starting levothyroxine at a dosage of 1.6 micrograms per kilogram of body weight per day (rounded to the nearest 25 micrograms) for adults under 65 with primary hypothyroidism and no history of cardiovascular disease.

Also here

cks.nice.org.uk/topics/hypo...

gp-update.co.uk/Latest-Upda...

Traditionally we have tended to start patients on a low dose of levothyroxine and titrate it up over a period of months. RCT evidence suggests that for the majority of patients this is not necessary and may waste resources.

For patients aged >60y or with ischaemic heart disease, start levothyroxine at 25–50μg daily and titrate up every 3 to 6 weeks as tolerated.

For ALL other patients start at full replacement dose. For most this will equate to 1.6 μg/kg/day (approximately 100μg for a 60kg woman and 125μg for a 75kg man).

If you are starting treatment for subclinical hypothyroidism, this article advises starting at a dose close to the full treatment dose on the basis that it is difficult to assess symptom response unless a therapeutic dose has been trialled.

BMJ also clear on dose required

bmj.com/content/368/bmj.m41

bestpractice.bmj.com/topics...

[NJB1418]

I was in a similar situation. It took a long time to regulate I can’t remember how long sorry but at least a year. I have been on 75mcg for approx 2 years now and tsh has maintained around 1.6 so just be patient I think. Hope that helps

[Yogamat123]

Thank you so much for your replies, really helpful. I will feel confident in asking the GP for an increase in dose tomorrow. I will ask for the thyroid hormones to be tested next time, as I don’t think they’ve been tested in the past. The vitamin D and B I requested last time as I’d read on here it’s common to be deficient. They were ok luckily. It’s good to know it can be a slow process to reduce the TSH