This is the version of the explanation I wish somebody had given me, written down before I forget what confused me. It is about oral semaglutide, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
Oral semaglutide is absorbed in the stomach with the help of SNAC, which locally raises pH and protects the peptide long enough to cross. That mechanism is fragile: bioavailability is roughly 1% and highly sensitive to gastric contents, so a mouthful of coffee genuinely changes the exposure. This is why the label wants 30 minutes and no more than half a glass of plain water.
The condition it depends on
The absorption variability is real, but it partly averages out over weeks — the steady-state trough is less erratic than any single day would suggest. Where it bites is in the first fortnight, when people conclude the tablet does nothing.
The practical version
The practical numbers: about 1% oral bioavailability, 30 minutes fasted before food, no more than 120ml of plain water, and coffee counts as food for this purpose.
What I am not sure about
The bit I cannot resolve on my own is how much of the oral variability is the SNAC absorption window and how much is dose, because the two get conflated constantly. I would rather have one careful answer than five confident ones.
— amy_econ_NJ · corrections welcome and will be edited into this post with credit