FTA: "So to summarize the state of the art in oral peptide delivery: there are exactly two FDA-approved products that use permeation enhancers to get peptides into your bloodstream through your GI tract. Both achieve sub-1% bioavailability. Both required over a decade of development, thousands of clinical trial participants, and hundreds of millions of dollars."
Injection is really the only method with any substantial bioavailability. BUT, low (<1%) bioavailability does not necessarily mean useless.
Can you say more about that point ?
Injectable Semaglutide/Tirzepatide (>99.8% pure) are currently sold at a profit from China for around $2-3/weekly dose. Rybelsus (oral semaglutide) is sold at roughly the same cost per milligram, even though it's made in FDA-approved facilities (you just need to take >= 40x more milligrams per month, bringing it to $1000/month in the USA)
So manufacturing oral doses 100x higher than injectable seems to be economically viable.
Cyclization + N-methylation — lipophilicity, protease resistance (cyclosporine)
D-amino acid substitution — protease evasion (desmopressin)
Permeation enhancers — transient tight-junction opening or membrane fluidization (semaglutide/SNAC, insulin formulations)
Extreme potency — tolerating <1% bioavailability (desmopressin)
Minimizing size to di/tripeptides — exploiting PepT1 active transport (collagen hydrolysates)
Prodrug masking — protecting reactive groups, intracellular unmasking (S-acetyl-glutathione)
Local buffering — pH microenvironment control (semaglutide)
One I take, PEP19, apparently is unique in being naturally bioactive. Evidence is early stage, but I get noticably better sleep with it (by some non-drowsiness mechanism), taking 6mg, 3x the recommended dosage for sleep, but the higher dose may promote fat burning and fat browning at night (only 1 study). It only has 10 residues which apparently avoid having typical cleavage points, fragments may retain bioactivity, and it has extreme potency in very small doses so any absorption means a lot.
Despite a plethora of peptides, successes are not common.