Original reference · reviewed July 1, 2026
Peptide Half-Life & Administration Route
How are peptides actually taken, and how long do they last? A physician-reviewed reference of administration route, half-life, and dosing frequency for 16 common molecules, with honest flags where human data does not exist.
Two practical questions decide how a peptide fits a person's life: how it is taken (injection, oral, topical, IV), and how long it lasts (the half-life, which sets the dosing frequency). This table answers both. For approved peptide drugs, half-lives are well established from human pharmacology. For unapproved “wellness” peptides, human pharmacokinetics often do not exist, and those rows say so instead of inventing a number.
This is dose-free by design. “Frequency” is general cadence (once weekly, daily), not a dosing instruction. For whether a given peptide is FDA-approved, see our FDA-approved peptides reference; for the peptide-versus-small-molecule distinction, see is it a peptide?.
The Reference Table — Route, Half-Life, Frequency
“Established (FDA-labeled)” = half-life from approved-drug human pharmacology. “Established pharmacology” = reasonably characterized but not all from a U.S. label. “Human PK not established” = no reliable human half-life data exists; animal data or trial estimates only.
Why Peptides Are Usually Injected
A peptide is a chain of amino acids. The stomach and gut are built to tear amino-acid chains apart; that is digestion. Swallow most peptides and they are destroyed before they reach the bloodstream. Injecting under the skin bypasses the gut entirely, which is why the GLP-1 weight-loss drugs (semaglutide, tirzepatide) are weekly subcutaneous injections rather than ordinary pills. An oral semaglutide formulation does exist, but it needs a special absorption enhancer and careful dosing conditions to survive.
Smaller peptides used in skincare, like GHK-Cu, are applied topically, but topical absorption of larger injected peptides is unreliable. NAD+ (not a peptide) is usually given by IV because oral NAD+ is poorly absorbed. The route is not a marketing choice; it follows from the molecule's chemistry.
Why Half-Life Drives the Schedule
Half-life is the time for the blood level of a drug to fall by half. It sets how often a peptide has to be given to keep a steady effect. A once-weekly GLP-1 like semaglutide (half-life about one week) fits ordinary life far better than a twice-daily injection. Short-acting peptides like sermorelin disappear from blood within minutes but their hormone-stimulating effect lasts hours, which is why they are given daily, often at night. CJC-1295 with DAC is chemically engineered to bind a blood protein and stretch its half-life to roughly a week.
For unapproved peptides, the honest caveat matters: where human half-life has never been measured, any “protocol” you see online is a guess, usually copied from rodent studies. That uncertainty is a core reason these belong under physician supervision, not self-directed from a website.
Frequently Asked Questions
Why are most peptides injected instead of taken as a pill?
Because peptides are chains of amino acids, stomach acid and digestive enzymes break them apart before they reach the bloodstream. Injecting under the skin (subcutaneously) skips the gut. This is why GLP-1 drugs like semaglutide and tirzepatide are weekly injections. An oral semaglutide formulation does exist, but it requires an absorption enhancer and specific dosing conditions to survive the gut.
What is the half-life of semaglutide?
About one week (roughly 165 hours), which is exactly why it is dosed once weekly. Tirzepatide is similar at about five days. Liraglutide is much shorter, around 13 hours, so it is dosed once daily.
What is the half-life of BPC-157?
The honest answer is that the half-life of BPC-157 in humans has not been established. Nearly all of its pharmacology comes from animal models. Anyone quoting a precise human half-life for BPC-157 is guessing. The same is true for TB-500, MOTS-c, and most other unapproved wellness peptides.
How often is sermorelin taken if its half-life is so short?
Sermorelin disappears from the bloodstream within minutes, but its effect — prompting your body to release its own growth hormone — lasts longer. That is why it is typically given as a daily injection, often at night to mirror natural growth-hormone rhythm. CJC-1295 with DAC is engineered to last much longer (about a week) by binding to a blood protein.
Why do half-lives matter for peptide therapy?
Half-life determines how often a peptide has to be taken, which drives convenience, cost, and how steady the effect is. A once-weekly GLP-1 fits most lives far better than a twice-daily injection. Half-life also hints at how quickly a drug clears if side effects occur.
Can peptides be absorbed through the skin?
Some small peptides are used topically in skincare, GHK-Cu being the best-known example, but skin absorption of larger injected peptides is unreliable. Topical use is a different category from injectable peptide therapy and should not be assumed to deliver comparable systemic effects.
Is NAD+ a peptide, and how is it given?
NAD+ is not a peptide — it is a nucleotide coenzyme (see our is-it-a-peptide classifier). It is most commonly given by IV infusion because oral NAD+ is poorly absorbed; oral precursors like NMN and NR are used instead. Its half-life in the blood is very short, measured in minutes to hours.
Are the half-lives of unapproved peptides reliable?
Often not. For FDA-approved peptide drugs, half-life is well characterized from human pharmacology. For unapproved research peptides, human pharmacokinetics are frequently unknown, and any number quoted usually comes from rodent data or is simply made up. This is one reason physician supervision and licensed-pharmacy sourcing matter.
Do you offer these as injections at your Las Vegas clinic?
LiveNow Longevity provides physician-supervised peptide therapy using licensed U.S. compounding pharmacies, with routes and cadences determined by your evaluation. Not every peptide is appropriate for every person, and some are not appropriate for clinical use at all. The route and frequency that fit you are decided with Dr. Kamen, not picked from a website.
How long until I notice effects from peptide therapy?
It depends on the peptide and the person. Some effects track the drug reaching steady levels over days to weeks; benefits like body-composition change with GLP-1s develop over months. We track your response against your own follow-up data rather than promising a fixed timeline.
Selected Research
Background sources supporting the pharmacology on this page.
- Müller TD, et al. Mol Metab. 2019;30:72-130. (Glucagon-like peptide 1 (GLP-1): physiology, satiety, and metabolism.)
- Wilding JPH, et al. N Engl J Med. 2021;384(11):989-1002. (STEP 1: once-weekly semaglutide in adults with overweight or obesity.)
- Walker RF. Clin Interv Aging. 2006;1(4):307-308. (Sermorelin for adult-onset growth hormone insufficiency.)
- Cerovecki T, et al. J Orthop Res. 2010;28(9):1155-1161. (BPC-157 and ligament healing in the rat — animal-model evidence.)
Reviewed by Dr. Charles Kamen, MD — board-certified neurologist, LiveNow Longevity, Las Vegas. Educational reference, not medical advice or dosing instructions.
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