What Is Peptide Half-Life?
Half-life (t½) is the time required for the plasma concentration of a compound to decline by 50% from its peak value. For a peptide with a 4-hour half-life administered subcutaneously, plasma concentration will be at ~50% of peak at hour 4, ~25% at hour 8, ~12.5% at hour 12, and so on — declining exponentially until effectively cleared.
For research peptides, half-life is shaped by four primary variables:
Enzymatic Degradation
Serum proteases cleave peptide bonds. Small, linear, unmodified peptides are cleaved within minutes. The primary driver of short t½ in most research peptides.
Renal Clearance
Peptides below ~50 kDa are filtered by the glomerulus. Small peptides (under 10 AA) clear rapidly. Larger analogs or those bound to albumin escape filtration.
Molecular Size & Structure
Cyclic, PEGylated, or fatty acid–conjugated peptides resist protease cleavage and kidney filtration, extending t½ from minutes to days.
Route of Administration
IV gives the shortest measured t½ (immediate exposure, fast clearance). SubQ adds an absorption phase, extending apparent t½. Oral: near-zero for unmodified peptides.
Albumin Binding
Peptides engineered to bind plasma albumin (half-life ~19 days) borrow its long circulation time. CJC-1295 DAC uses this mechanism to extend t½ from 30 minutes to 6–8 days.
D-Amino Acid Substitution
Replacing L-amino acids with their D-isomers at protease-vulnerable sites blocks enzymatic cleavage, extending t½ without changing receptor binding substantially.
Figure 1 — Peptide Plasma Concentration: Exponential Decay (Single Dose, SubQ)
Plasma concentration follows an exponential decay curve — halving at every half-life interval. Steady state (not shown) is achieved when dosing rate equals clearance rate after 4–5 half-lives.
Key Distinction
Half-Life ≠ Duration of Effect
A peptide can clear from plasma rapidly while its downstream biological effects persist for hours or days. GHK-Cu has an estimated plasma t½ of ~1 hour but initiates gene expression cascades that operate over days. Researchers must distinguish pharmacokinetic (PK) half-life from pharmacodynamic (PD) duration of effect — they are not the same measurement.
Figure 2 — Structural Modifications That Extend Peptide Half-Life
Structural engineering extends peptide half-life across 4 primary strategies. GLP analogs combine fatty acid conjugation with receptor design for multi-day persistence.
Why Half-Life Matters for Research Protocols
Half-life directly determines three critical protocol design decisions:
- Dosing interval. To maintain target plasma concentrations above a minimum threshold, the dosing interval must not exceed the point where clearance drops below the effective range. A 4-hour t½ compound generally requires daily or twice-daily administration; a 6-day t½ compound needs only weekly dosing.
- Steady-state timing. Steady state — consistent plasma levels with regular dosing — is reached after approximately 4–5 half-lives. For a 4-hour compound dosed every 4 hours, steady state arrives in ~20 hours. For a 6-day compound, it takes ~30 days. This affects when researchers should begin collecting outcome measurements.
- Washout period. Between protocol phases or before endpoint tissue collection, researchers often require a washout period to allow plasma clearance. This is typically 5 half-lives (reduces plasma levels to ~3% of steady state). A 4-hour compound needs a 20-hour washout; a 6-day compound needs a 30-day washout.
Visual Half-Life Comparison
Master Half-Life Reference Table
Values represent approximate plasma half-life based on the best available evidence as of June 2026. Where formal human pharmacokinetic studies exist, those values are used. Where only preclinical or estimated data exists, that is noted in the data quality column. Always consult individual compound literature and your institution's protocols for research design decisions.
Table 1 — Peptide Half-Life Master Reference (June 2026)
| Compound | Plasma t½ | PK Category | Route (Ref.) | Dosing Freq. | Data Quality |
|---|---|---|---|---|---|
| GLP-3 RT (Retatrutide) | ~6 days | Ultra-Long | SubQ | Weekly | Clinical PK |
| GLP-2 TRZ (Tirzepatide) | ~5 days | Ultra-Long | SubQ | Weekly | Clinical PK |
| CJC-1295 (with DAC) | 6–8 days | Ultra-Long | SubQ | Weekly–biweekly | Clinical PK |
| TB-500 | ~2–3 days | Long | SubQ / IP | 2× weekly | Preclinical (Tβ4 analogy) |
| BPC-157 | 4–8 hours | Medium | SubQ / IP / oral | Daily–twice daily | Preclinical / estimated |
| Selank | ~2–3 hours | Medium | SubQ / intranasal | 1–2× daily | Preclinical / estimated |
| Semax | ~2 hours | Medium | Intranasal / SubQ | 1–2× daily | Preclinical / estimated |
| Tesamorelin | ~26 minutes | Short | SubQ | Daily | Clinical PK (FDA label) |
| GHK-Cu | 30 min–2 hours | Short | SubQ / topical | Daily (injectable) | Estimated |
| NAD+ | ~1 hour (IV) | Short | IV / SubQ | Daily–several times/wk | Limited human data |
| CJC-1295 (no DAC / Mod GRF 1-29) | ~30 minutes | Short | SubQ | 2–3× daily (pulsatile) | Clinical PK |
| Sermorelin | ~10–20 minutes | Ultra-Short | SubQ / IV | Daily (bedtime) | Clinical PK (FDA label) |
| GHRP-2 | ~15–30 minutes | Ultra-Short | SubQ / IV | 2–3× daily | Limited human PK |
| GHRP-6 | ~15–30 minutes | Ultra-Short | SubQ / IV | 2–3× daily | Limited human PK |
| Ipamorelin | ~2 hours | Medium | SubQ / IV | 1–2× daily | Preclinical / estimated |
| Hexarelin | ~2–3 hours | Medium | SubQ / IV | 1–2× daily | Preclinical / estimated |
| PT-141 (Bremelanotide) | ~2.7 hours | Medium | SubQ / intranasal | As-needed (single dose) | Clinical PK (FDA label) |
| Epithalon | ~1–3 hours* | Short | SubQ / IV | Daily (cycled) | Estimated |
| DSIP (Delta Sleep-Inducing Peptide) | ~2 minutes (IV) | Ultra-Short | IV (mainly) | Pre-sleep / as-needed | Limited human data |
| Melanotan II | ~2–3 hours | Medium | SubQ | Daily–every other day | Preclinical / estimated |
* = Estimated from preclinical data, analogy to parent molecules, or detection window analysis. No formal published human pharmacokinetic study available as of June 2026. All values are research reference data, not dosing guidance.
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PK Categories Explained
Ultra-Short (<30 min)
Short (30 min–2 h)
Medium (2–12 h)
Long (12 h–3 days)
Ultra-Long (>3 days)
Table 2 — PK Category Guide
| Category | t½ Range | Typical Examples | Protocol Implication | Structural Basis |
|---|---|---|---|---|
| Ultra-Short | <30 min | Sermorelin, DSIP, GHRH fragments | Pulsatile timing critical; peak occurs within minutes; dose before sleep or fast for GH protocols | Small, unmodified; rapid protease cleavage and renal clearance |
| Short | 30 min–2 h | GHK-Cu, CJC-1295 no DAC, Epithalon | Daily injection typically required; downstream effects may outlast plasma presence | Small linear peptides; cleared by proteases; some receptor-mediated internalization |
| Medium | 2–12 h | BPC-157, Selank, Semax, Ipamorelin | Once or twice daily protocols; most common category in tissue repair research | Moderate size or stability; partial resistance to proteolysis |
| Long | 12 h–3 days | TB-500, some analogs | 2× weekly sufficient; simpler protocol design; easier steady-state maintenance | Larger molecular size; natural or partial protease resistance |
| Ultra-Long | >3 days | Retatrutide, Tirzepatide, CJC-1295 DAC | Once weekly dosing; long washout periods needed; extended steady-state timeline | Fatty acid conjugation, albumin binding, or engineered protease resistance |
Half-Life & Dosing Frequency Reference
This table provides a practical reference for research protocol design based on half-life. Values represent general guidelines derived from pharmacokinetic principles — individual compound protocols may differ based on receptor kinetics and endpoint requirements.
Figure 3 — Dosing Frequency Timeline by PK Category (7-Day Reference)
Figure 3 — Dosing frequency across PK categories over a 7-day window. Ultra-long compounds (Retatrutide, Tirzepatide) require only one injection per week; ultra-short GH secretagogues may require 2–3 injections daily timed to GH pulses.
Table 3 — Half-Life to Protocol Design Reference
| Half-Life | Min. Dosing Interval | Time to Steady State | Washout (5× t½) | Protocol Notes |
|---|---|---|---|---|
| 10–30 min | 3–4 × daily (or pulsatile) | 1–2 hours | ~2.5 hours | Timing precision critical; pulsatile dosing typically used to mimic endogenous rhythm |
| 1–2 hours | 2–3 × daily | 5–10 hours | ~10 hours | Daily morning + evening protocols common in rodent models |
| 4–8 hours | Once–twice daily | 20–40 hours | ~1.5–2 days | Most common category; BPC-157 sits here; once daily is standard in most protocols |
| 1–3 days | 2–3 × weekly | 5–15 days | ~5–15 days | TB-500 range; 2× weekly protocols provide stable exposure |
| 5–7 days | Once weekly | ~30 days | ~30–35 days | GLP analogs; once-weekly sufficient; plan 4+ weeks before measuring steady-state outcomes |
Understanding Data Quality
The half-life values in this chart come from different evidence tiers. Not all half-life numbers are equally reliable, and researchers designing protocols need to understand the basis for each figure.
Table 4 — Data Quality Tiers
| Quality Badge | Definition | Reliability | Examples in Chart |
|---|---|---|---|
| Clinical PK | Formal pharmacokinetic study in human subjects with measured plasma concentrations over time | Highest — direct human data | Retatrutide, Tirzepatide, Tesamorelin, Sermorelin, PT-141 |
| Limited Human | Small human studies (n<20), case series, or single-route PK data without full characterization | Moderate — directionally useful, not definitive | NAD+, GHRP-2, DSIP |
| Preclinical | Animal model pharmacokinetic data (rat, mouse) — may not translate directly to human | Lower — useful for protocol design but treat as approximate | BPC-157, Selank, Semax, GHK-Cu |
| Estimated | Inferred from detection windows, structural analogy, molecular modeling, or community literature without formal study | Lowest — use as rough orientation only | Epithalon, some GHRPs at specific routes |
📋 Important Note on BPC-157 Half-Life
BPC-157's frequently cited 4–8 hour half-life is an estimate derived from animal pharmacokinetic models and detection window data from a limited 2025 pilot study (IV, n=2). No formal, published human pharmacokinetic study with complete t½ determination exists for BPC-157 as of June 2026. Researchers should design protocols with this uncertainty in mind and build in appropriate measurement timepoints to bracket the effective window.
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Frequently Asked Questions
What is peptide half-life?
Peptide half-life (t½) is the time required for the plasma concentration of a peptide to decline by 50% from its initial value. It is shaped by enzymatic degradation by serum proteases, renal clearance, molecular size, and structural modifications. Short, unmodified peptides may clear in minutes; engineered analogs can persist for days.
Which research peptide has the longest half-life?
Among common research peptides, GLP receptor agonists engineered with fatty acid chains have the longest half-lives. Retatrutide (GLP-3 RT) is approximately 6 days. Tirzepatide (GLP-2 TRZ) is approximately 5 days. CJC-1295 with DAC achieves 6–8 days via albumin binding. All values from clinical pharmacokinetic studies.
What is BPC-157 half-life?
BPC-157's half-life is estimated at 4–8 hours based on animal pharmacokinetic models. No formal published human PK study with complete half-life determination exists as of June 2026. The relatively short half-life is why most preclinical BPC-157 protocols use daily administration.
What is TB-500 half-life?
TB-500 has an estimated half-life of 2–3 days based on parent molecule Thymosin Beta-4 pharmacokinetic data. This longer estimated half-life supports twice-weekly dosing protocols used in preclinical models, rather than the daily dosing required for shorter-acting peptides like BPC-157.
Why do some peptides have very short half-lives?
Short, linear, unmodified peptides are rapidly degraded by serum proteases — enzymes that circulate in blood and cleave peptide bonds. Small peptides are also rapidly filtered by the kidneys. Structural modifications — D-amino acid substitutions, PEGylation, fatty acid conjugation, albumin binding — can extend half-life from minutes to days.
How does half-life affect research protocol dosing frequency?
Half-life directly determines dosing interval. A compound with a 4-hour half-life requires dosing every 4–8 hours to maintain target plasma concentrations; a 6-day half-life compound needs only weekly administration. Steady state is typically reached after 4–5 half-lives of regular dosing.
Is half-life the same as duration of effect?
No. Half-life describes how long the peptide remains in circulation; effect duration requires independent study. GHK-Cu, for example, has a short plasma half-life (~1 hour) but initiates gene expression changes that persist for days. Half-life informs dosing frequency — not how long downstream effects last.
What is the half-life of GHK-Cu?
GHK-Cu has a short estimated plasma half-life of approximately 30 minutes to 2 hours. The tripeptide is rapidly cleared, but its downstream effects on gene expression and collagen synthesis persist substantially longer. This is a common pattern in small peptide research — short PK window, extended PD effects.
What does 'data quality' mean in a peptide half-life chart?
Data quality refers to the evidence tier behind a reported half-life value. Clinical PK = formal human pharmacokinetic study. Preclinical = animal model data. Estimated = inferred from detection windows or structural analogy. Most research peptides lack formal human PK studies — their half-lives are estimates that should be treated accordingly in protocol design.
How does route of administration affect half-life?
IV gives the shortest measured t½ (immediate systemic exposure, fast clearance). SubQ adds an absorption phase that extends apparent t½ — the peptide absorbs slowly from the injection site. Oral administration of unprotected peptides results in near-complete GI protease degradation before absorption, making oral bioavailability effectively zero for most unmodified peptides.
What is steady-state plasma concentration?
Steady state is when the rate of peptide administration equals the rate of clearance — a stable, consistent plasma level. Achieved after approximately 4–5 half-lives of regular dosing. For a 4-hour t½ compound dosed every 4 hours, steady state arrives in ~20 hours. For a 6-day t½ compound dosed weekly, it takes ~30 days.
Which peptides have the shortest half-lives?
GHRH analogs like Sermorelin (~10–20 min) and CJC-1295 without DAC (~30 min) have very short half-lives, as do GHRPs like GHRP-2 and GHRP-6 (15–30 min). DSIP has a plasma t½ of approximately 2 minutes via IV — among the shortest of any research peptide. These short half-lives are why GH secretagogue protocols time injections precisely around sleep onset or fasting states.
Research Use Disclaimer — All peptide half-life data presented here is for in vitro laboratory research reference only. All values are approximate and sourced from published pharmacokinetic literature, preclinical models, or estimation. This information does not constitute medical advice, dosing guidance, or therapeutic recommendation. Evo Peptides products are sold for research use only and are not intended for human consumption.