How peptides work in your body.
Many peptides work as messages. Where the message lands, how long it lasts and how it gets in decide almost everything about the schedule.
- Some peptides carry messages between cells. A receptor is the molecule that picks up the message and starts a response.
- Half-life is how fast the body clears a dose. Semaglutide's is about 1 week; tesamorelin (Egrifta WR) is a mean 11 minutes.
- Half-life shapes the schedule: semaglutide and tirzepatide are weekly shots, tesamorelin is daily.
- Swallowed peptides are poorly absorbed. Semaglutide under the skin is about 89% absorbed; Wegovy tablets about 1 to 2%.
- For many research peptides, like BPC-157, the human half-life is simply unknown.
A message, and something to read it
Binding, switching on and the effect that follows are separate steps. The GLP-1 drugs show how much the target matters: each one reads a different set of hormone signals.
- Semaglutide GLP-1 receptor only.
- Tirzepatide GIP and GLP-1 receptors.
- Retatrutide GLP-1, GIP and glucagon receptors.
Half-life sets the rhythm
A long half-life means steady levels from a weekly shot. A short one means a quick pulse that fades within the hour.
- Semaglutide About 1 week
- Retatrutide About 6 days in early studies
- Tirzepatide About 5 days
- PT-141 (Vyleesi) Mean 2.7 hours
- Tesamorelin (Egrifta WR) Mean 11 minutes
- BPC-157 Unknown in humans
It also explains slow exits. Semaglutide can stay in the blood about 5 to 7 weeks after the last dose, which is why its label says to stop at least 2 months before a planned pregnancy.
Why most of them are shots
Under the skin, most of a dose reaches the blood. By mouth, very little does, so tablets need an absorption helper and their milligrams mean something else.
Oral and injectable milligrams are not interchangeable. Nasal milligrams can't be swapped for injection milligrams either.
Next: Lesson 3: The main
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