Peptide Half-Life Reference

What Half-Life Means

The plasma half-life of a peptide is the time it takes for its concentration in blood plasma to fall by half. It is the standard measure of how quickly the body clears a compound.

The decay is exponential, which has a useful consequence. After one half-life, half the peak concentration remains. After two, a quarter. After three, an eighth. By roughly four to five half-lives, the compound is largely cleared — down to about 3–6% of peak. This is why half-life, a single number, tells you so much: it sets the entire timescale on which a peptide rises and falls in circulation.

For a peptide with a 30-minute half-life, that whole arc plays out in about two to three hours. For one with a 7-day half-life, it stretches across a month. That span — minutes to weeks — is the subject of this reference.

This is the pharmacokinetics-focused companion to the Peptide Database and the Molecular Weight Database. Where those index peptides by class and by mass, this one sorts them by how long they persist.

The Range — Minutes to Days

The most striking thing about peptide half-life is the sheer scale of the range. Across this database it spans roughly four orders of magnitude — from peptides cleared in about a minute to peptides that persist for a week.

Bars are scaled to illustrate relative magnitude across the range; they are not to precise linear scale, since a true linear scale would render the minute-range peptides invisible next to the day-range ones.

Master Table — Sorted by Half-Life

All 45+ compounds, ordered from shortest to longest approximate plasma half-life. Sorting this way groups peptides by their natural dosing rhythm.

* "Typical dosing rhythm" describes the administration frequency reported in published research literature — it reflects the cadence half-life implies, not a dosing recommendation. ** Semax and Selank: plasma half-life is on the order of minutes, but reported central effects outlast plasma presence — see Plasma Half-Life vs Duration of Effect. Compounds with a qualitative entry (e.g. "intermediate") have less firmly established published pharmacokinetic data; see Why These Values Are Approximate. NAD+, 5-Amino-1MQ, Methylene Blue, Glutathione, and the peptide mixtures are omitted here as their pharmacokinetics fall outside a simple peptide half-life framing.

The Five Half-Life Classes

Sorting by half-life reveals five natural bands. Each band shares a characteristic clearance mechanism and a characteristic dosing rhythm.

How Half-Life Drives Dosing Frequency

Half-life is the single most important factor in how often a compound is administered in a research protocol. The logic is direct: to keep a compound's concentration within a useful window, you re-administer on a timescale set by how fast it clears.

• Ultra-short and short half-life peptides fall out of circulation within hours. Research protocols that aim to sustain exposure use frequent administration — often one to three times daily. The GHRH analogs and GHRPs sit here.
• Intermediate half-life peptides — BPC-157, Ipamorelin, TB-500 — are commonly studied with daily or several-times-weekly administration.
• Long and ultra-long half-life compounds persist for days. The lipidated GLP-1 agonists are the defining example: their ~5–7 day half-life is precisely what makes once-weekly administration possible in research settings. The long half-life is not incidental — it was the design goal.

Plasma Half-Life vs Duration of Effect

This is the most misunderstood point in peptide pharmacokinetics, and it is worth stating plainly: plasma half-life is not the same as duration of effect.

Plasma half-life measures one specific thing — how long the peptide molecule itself remains in blood plasma. Duration of effect measures something different — how long the biological response persists. The two are related, but they can diverge substantially.

The clearest example is the nootropic peptide class. Semax and Selank both have a plasma half-life measured in minutes — the peptides are cleared from circulation very quickly. Yet their reported central effects persist far longer than their plasma presence. The peptide triggers a downstream cascade — changes in signaling, in expression of other factors — and that cascade outlasts the molecule that set it in motion.

The same logic appears elsewhere. A peptide that drives a structural or regenerative process may produce effects that continue well after the compound clears. So a short plasma half-life does not reliably mean a short-lived effect.

How Peptides Are Engineered to Last Longer

Native peptides are, as a rule, cleared fast. The body is efficient at breaking down peptide molecules — enzymes such as DPP-4 cleave them, and the kidneys filter them out. A natural signaling peptide doing its job in the body often has a half-life of just a minute or two.

Every long-half-life peptide in this database is long-acting because someone designed it to be. The main strategies:

• Fatty-acid acylation (lipidation). Attaching a fatty-acid chain lets the peptide bind to albumin, the most abundant protein in blood plasma. Albumin-bound peptide is shielded from clearance and released slowly. This is the mechanism behind Semaglutide and Tirzepatide — and it is why their half-lives are measured in days.
• The Drug Affinity Complex (DAC). CJC-1295 with DAC carries a chemical group that binds to blood proteins, extending its half-life from the ~30 minutes of the un-modified version to roughly 6–8 days. Same peptide backbone, radically different pharmacokinetics.
• Amino acid substitution. Swapping in residues that degradation enzymes do not recognize — for example, the non-standard amino acid Aib used in several incretin agonists, or the substitutions that distinguish CJC-1295 no DAC (Modified GRF 1-29) from native Sermorelin. This blocks the cleavage site and slows clearance.
• Structural stabilization. Cyclization and other backbone modifications can make a peptide inherently more resistant to enzymatic attack.

Understanding which mechanism is in play explains otherwise puzzling pairs — like why two versions of "CJC-1295" sit at opposite ends of this database's half-life table.

Why These Values Are Approximate

Half-life is not a single fixed constant for a given peptide. Published values vary, sometimes considerably, and this reference uses approximate figures and ranges deliberately. The main reasons values differ:

• Species. Much peptide pharmacokinetic data comes from animal models. Half-life in one species does not transfer exactly to another.
• Route of administration. Subcutaneous, intramuscular, intravenous, oral, and intranasal routes produce different absorption and clearance profiles for the same peptide.
• Assay method. Different analytical methods measuring the same sample can report somewhat different half-lives.
• Distribution vs elimination phase. Many peptides show a fast initial drop (distribution) followed by a slower decline (elimination). Sources sometimes report different phases, which is one reason published numbers diverge.
• Formulation. Especially for engineered long-acting peptides, the specific formulation affects the observed half-life.

Entries in the master table marked qualitatively — "intermediate," "short–intermediate" — are compounds for which firm, consistent published pharmacokinetic data is harder to pin down. They are placed in the band the available evidence supports, without a false-precision number.