Short answer: even “microdosing” tirzepatide probably bumps GLP-1 receptor signaling by roughly one to two orders of magnitude above normal physiology, at least around peak levels. So, yes, even the “baby” doses are not subtle.

I’ll walk through the logic, since I know you care about the actual numbers:

1. Baseline endogenous GLP-1 levels

Active (“intact”) GLP-1 in plasma is tiny:

• Fasting: typically < 2 pmol/L active GLP-1
• Post-meal: ~5–10 pmol/L, sometimes up to ~40 pmol/L in more “exuberant” responses depending on assay / meal size

In molar terms, that’s roughly:

• “Ordinary” postprandial: 5–10 pmol/L → 0.005–0.01 nM
• Rare higher end: 40 pmol/L → 0.04 nM

So your gut is playing in the 10⁻³–10⁻² nM range most of the time.

2. Tirzepatide potency at GLP-1R

In vitro signaling data:

• At GLP-1R, tirzepatide is ~13× less potent than native GLP-1 for cAMP (EC50 ≈ 934 pM vs 70.5 pM)
• So to get the same GLP-1R activation as 1 nM GLP-1, you need ~13 nM tirzepatide.

So it’s a “weaker” GLP-1 agonist per molecule, but you are delivering massive amounts of it.

3. Tirzepatide plasma levels at standard doses