TSH moving on cutting cycle — context: down 18 lbs in 10 weeks
40 posts
Not sure if this is a peptide question, a caloric deficit question, or both, so posting here.
On tirz 5mg/week, 10 weeks in, down 18 lbs. Pulled thyroid labs.
Baseline:
- TSH: 1.8 mIU/L
- Free T4: 1.3 ng/dL
- Free T3: 3.2 pg/mL
Week 10:
- TSH: 3.1 mIU/L
- Free T4: 1.2
- Free T3: 2.7
TSH almost doubled, Free T3 dropped 16%. Still 'in range' but directionally this is the classic 'cutting phase thyroid suppression' shape.
Is this the GLP-1 or the deficit? And is a TSH of 3.1 something to act on or just ride out?
8 Replies
40 posts
That's the deficit, not the GLP-1. Prolonged caloric deficit + significant weight loss reliably nudges TSH up and pulls T3 down. It's the body's adaptive response — 'less fuel coming in, lower thyroid output'. Happens independent of any drug.
TSH 3.1 is nothing to act on. Free T4 is fine. It'll normalize within a few months of maintenance cals.
50 posts
Seconded. My TSH went 1.4 -> 2.9 during my biggest loss phase. Came back to 1.6 after 6 weeks of maintenance.
- Tirzepatide · 5 mg · weekly · sub-Q
29 posts
Free T3 is the meaningful one here and 3.2 -> 2.7 is a real drop (CV ~5-7%). But it's still well inside the reference range. Symptoms (temperature, bowel, energy) more than the number should drive any action.
- Sermorelin · 300 mcg · pre-bed · sub-Q
- Ipamorelin · 200 mcg · pre-bed · sub-Q
38 posts
Cold feet mid-cut is basically the body saying 'thank you for noticing, please eat'. Normal adaptation. Doesn't mean you need T3 or anything crazy.
51 posts
Seen this exact pattern twice on tirz cuts. Both times TSH climbed and T3 dipped but it all rebounded within 2-3 weeks of eating normal again. The GLP-1 definitely suppresses appetite which forces the deficit deeper than you'd naturally sit, so yeah, some thyroid adaptation is just gonna happen. If you feel fine energy-wise you're prob not destroying anything.