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TSH is checked 6 to 8 weeks after a Synthroid 75 mcg start or change
5 min readReviewed 21 August 2026. Updated
At a glance
Page typeNote
Strength75 mcg
Lab clock6–8 weeks
ReviewerCamille Rousseau, MD
Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. This note features 75 mcg. Peak therapeutic effect may not be attained for 4 to 6 weeks.
01The 6 to 8 week TSH clock
Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Peak therapeutic effect may not be attained for 4 to 6 weeks.
This note features 75 mcg. SYNTHROID is indicated as replacement therapy in primary, secondary, and tertiary hypothyroidism. The goal of replacement is a TSH in the reference range when that is the labelled target for the indication.
02Weight-loss use and the morning swallow
Do not use SYNTHROID for the treatment of obesity or for weight loss. Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast.
03How a 75 mcg tablet is adjusted
Titrate the dose every 6 to 8 weeks until the TSH is in the target range. Small milligram steps are written by the prescriber. Do not change 75 mcg on a home schedule because a single TSH print looked high.
In patients with primary hypothyroidism, TSH is the primary monitoring parameter. Free T4 may be used in central hypothyroidism when TSH is not the right marker.
How to cite this page - Vancouver style
Halo Medix Medicines Reference. TSH is checked 6 to 8 weeks after a Synthroid 75 mcg start or change [Internet]. Montreal: Halo Medix; 21 August 2026 [cited 2026 Aug 21]. Available from: https://halomedix.com/notes/synthroid-tsh-checks/
('Readers around Montreal asked when to recheck TSH on 75 mcg Synthroid. ', 'Answers follow the U.S. Synthroid label.')
Sophie Tremblay, Plateau asks
I started 75 mcg last week. When is the first TSH?
Reply from our reviewer
Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Peak therapeutic effect may not be attained for 4 to 6 weeks. This note features 75 mcg. A TSH drawn at day 7 is early for a replacement check on the labelled clock. The prescriber names the lab date.
Marc-Olivier Côté, Rosemont asks
Can I raise 75 mcg myself if I still feel tired at week 3?
Reply from our reviewer
Titrate the dose every 6 to 8 weeks until the TSH is in the target range. Small milligram steps are written by the prescriber. Do not change 75 mcg on a home schedule because a single feeling or a single TSH print looked high. In patients with primary hypothyroidism, TSH is the primary monitoring parameter.
Amina Benali, Saint-Léonard asks
Is TSH the right lab if my hypothyroidism is pituitary?
Reply from our reviewer
Free T4 may be used in central hypothyroidism when TSH is not the right marker. SYNTHROID is indicated as replacement therapy in primary, secondary, and tertiary hypothyroidism. Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose when TSH is the labelled marker.
Jonathan Reid, NDG asks
Does a TSH check change the empty-stomach rule?
Reply from our reviewer
Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast. The lab clock does not move that swallow. Do not use SYNTHROID for the treatment of obesity or for weight loss.
Luc Bergeron, Petite-Patrie asks
What tablet strengths sit next to the 75 mcg lock?
Reply from our reviewer
SYNTHROID tablets for oral administration are supplied as 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, and 300 mcg. This note features 75 mcg. Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Titrate the dose every 6 to 8 weeks until the TSH is in the target range. Peak therapeutic effect may not be attained for 4 to 6 weeks.
Amélie Saadi, Dollard-des-Ormeaux asks
Who reads TSH in primary hypothyroidism?
Reply from our reviewer
In patients with primary hypothyroidism, TSH is the primary monitoring parameter. Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Free T4 may be used in central hypothyroidism when TSH is not the right marker. SYNTHROID is indicated as replacement therapy in primary, secondary, and tertiary hypothyroidism. The prescriber names the lab date.
Patrick Gagné, Lachine asks
Does a TSH check allow a weight-loss indication?
Reply from our reviewer
Do not use SYNTHROID for the treatment of obesity or for weight loss. Doses within the range of daily hormonal requirements are ineffective for weight reduction. SYNTHROID is indicated as replacement therapy in primary, secondary, and tertiary hypothyroidism. SYNTHROID is not indicated for suppression of benign thyroid nodules.
Olivier Mansour, Plateau asks
Can biotin change a TSH print on 75 mcg?
Reply from our reviewer
Biotin supplements can interfere with immunoassays for TSH, T4, and T3. Stop biotin and biotin-containing supplements for at least 2 days before the draw. Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Peak therapeutic effect may not be attained for 4 to 6 weeks. This note features 75 mcg. In patients with primary hypothyroidism, TSH is the primary monitoring parameter.
Karine El-Amin, Longueuil asks
What T4 half-life range sits next to the 6 to 8 week clock?
Reply from our reviewer
The prescribing information gives a T4 half-life of 6 to 7 days in the usual state, 3 to 4 days in hyperthyroidism, and 9 to 10 days in hypothyroidism. Absorption of oral T4 runs 40% to 80%, mostly from the jejunum and upper ileum. Assess TSH 6 to 8 weeks after initiation or a change in SYNTHROID dose. Peak therapeutic effect may not be attained for 4 to 6 weeks. This note features 75 mcg. Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast. This note features 75 mcg. Titrate the dose every 6 to 8 weeks until the TSH is in the target range.
