TSH moving on cutting cycle — context: down 18 lbs in 10 weeks
36 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?
7 Replies
32 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.
44 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
27 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
31 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.