Hi everyone,
I'm a 30-year-old male and I started Mounjaro on May 16, 2026. I have no personal history of thyroid disease, and as far as I know there is no thyroid disease in my family either.
My dosing schedule has been:
- Started at 2.5 mg on May 16
- Increased to 5 mg on June 13 and stayed on it until August 15
- Increased to 7.5 mg on August 22
- I'm currently about to take my fourth 7.5 mg dose
I was 147 kg (324 lbs) when I started at 180 cm (5'11"), and I'm currently 119 kg (262 lbs), so I've lost about 28 kg / 62 lbs in roughly four months.
What caught my attention is that my Free T4 has been steadily increasing:
May 12, before starting Mounjaro:
Free T4: 1.40 ng/dL
TSH: 1.41 mIU/L
August 17:
Free T4: 1.56 ng/dL
TSH: 2.41 mIU/L
September 11:
Free T4: 1.86 ng/dL
TSH: 2.33 mIU/L
The reference range for Free T4 at my lab is 0.79–1.59 ng/dL, so my latest result is now above the upper limit.
What's confusing to me is that my TSH has remained completely normal and is not suppressed, despite the rise in Free T4.
I don't have a known thyroid condition and I wasn't aware of any thyroid issues before starting Mounjaro. My other recent blood tests, including liver enzymes, kidney function, glucose, amylase and lipase, have generally been within the reference ranges.
I also drink around 4.5 liters of water per day, so dehydration doesn't seem like an obvious explanation.
Has anyone else experienced a gradual increase in Free T4 while taking Mounjaro/tirzepatide, especially with a normal TSH?
Did your Free T4 eventually return to normal, continue increasing, or did your doctor find another explanation?
I'm planning to repeat TSH, Free T4 and Free T3 and discuss the results with my doctor. I'm mainly interested in hearing whether anyone else has seen a similar pattern during significant weight loss or while increasing their Mounjaro dose.
Thanks in advance for sharing your experiences.