Peptide bioavailability is the share of a dose that reaches your bloodstream unchanged, and it swings wildly by route. On FDA labels, injected peptides range from 36% to about 100%, a calcitonin nasal spray delivers 3% to 5% of an injection, and peptide tablets such as oral semaglutide absorb only about 0.4% to 2%.[7][8][11][2]
Below is a table of real numbers taken from prescribing information, followed by why the routes differ and what it means for unapproved peptides. New to peptides? Start at the peptide basics hub.
What bioavailability means
Bioavailability compares how much drug reaches the blood by one route with an intravenous (IV) dose, which counts as 100%. “Absolute” bioavailability is measured against IV. “Relative” bioavailability compares two non-IV routes, such as nasal versus injection.
A low number does not mean a drug fails. Manufacturers raise the dose to compensate, which is why a Wegovy tablet contains 25 mg of semaglutide while the weekly injection contains 2.4 mg.[1]
Bioavailability by route: label numbers
| Peptide (brand) | Route | Bioavailability | Source |
|---|---|---|---|
| Bremelanotide (Vyleesi) | Subcutaneous | About 100% | Label[8] |
| Teriparatide (Forteo) | Subcutaneous | About 95% | Label[6] |
| Semaglutide (Wegovy) | Subcutaneous | 89% | Label[1] |
| Tirzepatide (Zepbound) | Subcutaneous | 80% | Label[3] |
| Calcitonin salmon | Subcutaneous / intramuscular | 71% / 66% | Label[12] |
| Dulaglutide (Trulicity) | Subcutaneous | 65% (0.75 mg), 47% (1.5 mg) | Label[5] |
| Liraglutide (Saxenda) | Subcutaneous | About 55% | Label[4] |
| Abaloparatide (Tymlos) | Subcutaneous | 36% | Label[7] |
| Tesamorelin (Egrifta, 1 mg vial) | Subcutaneous | Less than 4% | Label[9] |
| Calcitonin salmon | Nasal spray | 3% to 5% of intramuscular | Label[11] |
| Semaglutide (Ozempic tablets, Wegovy tablets) | Oral | About 1% to 2% | Label[2][1] |
| Enlicitide (Lipfendra) | Oral | About 1% | Label[15] |
| Semaglutide (Rybelsus) | Oral | About 0.4% to 1% | Label[2] |
| Desmopressin (DDAVP tablets) | Oral | About 0.16% of IV; about 5% of nasal | Label[10] |
See our profiles for semaglutide, tirzepatide, liraglutide, dulaglutide, teriparatide, abaloparatide, tesamorelin and bremelanotide (PT-141).
Injections: high, but not always 100%
Under the skin, a peptide has to survive local enzymes and travel through tissue, sometimes via the lymphatic system, before reaching the blood.[16] Most approved injectables land between about 50% and 100%.
There are exceptions. Tesamorelin, a growth hormone-releasing factor analog, absorbs at less than 4% from its original 1 mg/vial formulation, so the dose was set accordingly.[9] Dulaglutide shows a size effect: absorption fell from 65% at 0.75 mg to 47% at 1.5 mg.[5]
For the trade-offs between shots under the skin and into muscle, see subcutaneous vs intramuscular injection.
Nasal sprays: fast but small
The nose has a thin, blood-rich lining, so absorption is quick. Calcitonin nasal spray peaks in about 13 minutes. Its bioavailability is only 3% to 5% of an intramuscular dose.[11]
Glucagon shows the same pattern in dosing. Nasal glucagon (Baqsimi) is given as 3 mg,[13] while an injected dose for adults is 1 mg.[14] More detail is in peptide nasal sprays vs injections.
Pills: the hardest route
Stomach acid, digestive enzymes and the gut lining all work against peptides.[16] Approved peptide pills reach about 1% by adding absorption enhancers: SNAC in oral semaglutide and sodium caprate in enlicitide.[2][15] Desmopressin tablets, with no such enhancer, reach about 0.16% of an IV dose.[10] Our guide to oral peptide delivery explains the technology.
Inhaled peptides: dose conversion tells the story
Insulin is a 51-amino-acid peptide hormone, and inhaled insulin (Afrezza) shows how route changes dosing even when the label gives no single bioavailability figure. People switching from injected mealtime insulin start with more inhaled units: up to 3 injected units converts to 4 inhaled units, 4 to 5 units to 8, 6 to 7 units to 12, and 8 or more to 16.[17] The conversion is set by the label, not by guesswork, and blood sugar monitoring is increased after a switch.
Bioavailability vs half-life
These two terms are often confused online. Bioavailability is how much of a dose gets in. Half-life is how long it stays. Natural GLP-1 has a half-life of only 1.5 to 2 minutes because enzymes break it down. Liraglutide was engineered to resist those enzymes and lasts about 13 hours, which suits daily dosing.[4] Semaglutide binds albumin and lasts about a week.[1] A drug can have high bioavailability and a short half-life, or the reverse.
Why this matters for your dose
Route-specific numbers explain why doses are never interchangeable between forms. A weekly semaglutide injection and a daily tablet use different amounts of the same molecule.[1][2] Switching between them follows label instructions set by a clinician, not simple arithmetic. The same logic applies to compounded or unregulated products: without a measured bioavailability, there is no reliable way to know how much reaches the blood.
What’s established vs preliminary
Established:
- Injections deliver most of a peptide dose, oral delivery very little.[1][2]
- Nasal delivery of peptides typically achieves a few percent of an injection.[11]
- Absorption can depend on dose and formulation, not just route.[5][9]
Preliminary or unknown:
- Bioavailability of BPC-157, TB-500 and other unapproved peptides in humans.
- Whether cosmetic peptides in creams reach meaningful levels beyond the skin. Most are designed to act locally; see peptide creams vs serums.
Limitations of these numbers
- Healthy volunteers. Many label studies used small groups of healthy adults, so patients may differ.
- Averages hide variation. Oral and nasal routes vary most between people. The Wegovy label notes greater variability in blood levels with tablets than with injections.[1]
- Bioavailability isn’t effect. A drug with lower absorption can still work well if the dose is set correctly. Clinical trial results, not absorption alone, show whether a product works.
- Product-specific. A number applies only to that formulation. Compounded or unregulated versions may behave differently, and storage matters too; see lyophilized vs premixed peptides.
What’s next
Drug makers are working to push oral peptide absorption higher with new enhancers, ring-shaped (cyclic) peptides and ingestible devices.[16] Longer-lasting options that avoid daily dosing are covered in peptide delivery technologies.
Questions to discuss with a clinician
- Is there more than one form of my medicine, and how do their doses compare?
- Could other drugs, food or acid reducers change how much I absorb?
- If I’m considering an unapproved peptide, is there any human data on how much reaches the blood?
- Would switching routes require a different dose?
