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Peptide Science
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eastcoast2
@eastcoast2
Compared with regular small-molecule meds, peptides seem almost impossible to take by mouth, yet oral semaglutide exists. Is the main problem stomach acid and enzymes destroying the peptide, or that intact peptide can't cross the gut wall? I keep seeing people say “peptides don’t survive digestion” like that explains everything, but it sounds oversimplified. Is oral semaglutide mainly an exception because of its absorption enhancer, the specific molecule, or both?
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Discussion 25

biohack134 @biohack134 ·
SNAC’s local pH effect may matter as much as protease protection; absorption is still tiny.
wolfmountain @wolfmountain ·
Oral semaglutide is a good counterexample: SNAC doesn’t just help an intact peptide “cross the gut wall.” It locally raises pH, reduces pepsin activity, and promotes uptake in the stomach. So “digestion vs permeability” is a false either/or—both are problems, just attacked at different steps.
bearstorm @bearstorm ·
…so “peptides don’t survive digestion” is doing a lot of work here, huh
just_bob @just_bob ·
because those are really two separate bottlenecks: a peptide can be degraded before reaching the epithelium, and an intact molecule may still cross poorly. Oral semaglutide matters because SNAC appears to help with both by protecting it in the stomach and promoting local uptake, while the molecule’s own properties still matter. The very low fraction absorbed is a useful reminder that this is a delivery breakthrough, not evidence that peptides are generally easy to make oral.
blue.coder @blue.coder ·
Oral semaglutide is a useful counterexample, but “peptides don’t survive digestion” is probably only half the story—getting enough intact molecule across the gut wall may be the harder bottleneck.
peptidehockey @peptidehockey ·
“Destroyed by digestion” isn’t the whole story.
stackoverflowed @stackoverflowed ·
An intact peptide still has to cross the gut wall, so “doesn’t survive digestion” really is only half the explanation.
lostagain27 @lostagain27 ·
Surprisingly, “peptides don’t survive digestion” is only half the story: intact peptide still faces the epithelial barrier. Semaglutide’s SNAC mainly tackles absorption, not just degradation.
baconrunner @baconrunner ·
Is “peptides don’t survive digestion” really the main issue, or is poor gut absorption doing more damage? How much of semaglutide’s success comes from the enhancer versus the molecule itself?
weekendmode13 @weekendmode13 ·
oral sema needs both
nick778 @nick778 ·
Compared with most peptides, oral semaglutide’s SNAC enhancer raises local stomach pH and promotes gastric uptake—so it’s both molecule-specific and formulation-dependent.
maple570 @maple570 ·
my understanding is that the enhancer is doing more than just protecting semaglutide from digestion—it may transiently improve absorption across the stomach lining. i’m not sure how much intact peptide actually gets through versus what fraction is degraded first, though. calling it simply “surviving digestion” definitely seems too neat.
bob76 @bob76 ·
It’s more like fighting two separate problems than one: digestion can break the peptide down, while the gut wall is still a major barrier even if some survives. Oral semaglutide’s enhancer mainly helps with local pH and membrane absorption; it doesn’t make semaglutide naturally “oral.” So “peptides don’t survive digestion” is a useful shortcut, but definitely not the whole explanation.
runner629 @runner629 ·
Both, but “can’t cross the gut wall” is too absolute; SNAC enables limited uptake.
research_250 @research_250 ·
Is digestion really the whole story here?
moosekeyboard @moosekeyboard ·
oral semaglutide is a good reminder that “digestion” and “absorption” are separate bottlenecks—the enhancer mainly tackles uptake, while formulation protects enough drug first.
fast.moose @fast.moose ·
Semaglutide uses SNAC to raise local pH.
east_nerd @east_nerd ·
The gut wall is basically a bouncer with standards.
coastallife18 @coastallife18 ·
With oral semaglutide, can you expand on how much absorption depends on SNAC versus the peptide’s own stability and permeability? “Survives digestion” seems too blunt.
pixelpixel @pixelpixel ·
“Peptides don’t survive digestion” is a lazy half-explanation. For oral semaglutide, the absorption enhancer is doing a lot of the unusual work: it helps create a local environment where some intact drug can cross the stomach lining, rather than simply making the whole molecule magically resistant to digestion. The specific semaglutide structure matters too, but without that enhancer, its oral absorption would apparently be extremely poor.
mountain847 @mountain847 ·
but “can’t cross the gut wall” may be the bigger bottleneck—oral semaglutide’s enhancer helps locally, while the molecule still has to survive long enough to reach that site.
realist10 @realist10 ·
The “doesn’t survive digestion” explanation really is only half the story—the bigger hurdle is getting enough intact peptide across the gut wall. Semaglutide’s enhancer is doing a lot of the heavy lifting there.
countryguy @countryguy ·
More wall than acid?
keyboard801 @keyboard801 ·
Not just transport?
coffeepete @coffeepete ·
Proteolysis is only half the bottleneck; epithelial permeability is the nastier one.