Dosing reference
Peptide Half-Life Explained: Why Dosing Frequency Varies
By Baris Bingor · Last updated
What is a peptide's half-life and why does it matter?
A peptide's half-life is the time for half of it to clear your system. It sets dosing frequency: long-half-life peptides like semaglutide (~7 days) or CJC-1295 with DAC (~8 days) are dosed about weekly, while short-half-life ones like Modified GRF 1-29 (~30 minutes) are dosed one or more times a day. Matching dose timing to half-life keeps levels steady — and Peptly reminds you on whatever schedule you set.
What "half-life" means
A peptide's half-life is the time it takes for half of the amount in your system to be eliminated. After one half-life, half remains; after two, a quarter; and after roughly four to five half-lives, the dose is essentially cleared. It is one of the most useful numbers to know about any compound, because it largely determines how often you dose.
Why dosing frequency follows half-life
The principle is simple: short half-life → frequent dosing; long half-life → infrequent dosing. If a peptide clears in 30 minutes, a once-weekly shot would leave you with almost nothing in the system most of the time, so protocols dose it often. If it lasts a week, a single weekly injection holds levels steady. Dosing frequency is essentially an attempt to keep the amount in your body within a useful range given how fast it disappears.
Half-life by peptide (approximate)
| Peptide | Approx. half-life | Typical dosing cadence |
|---|---|---|
| Modified GRF 1-29 (CJC-1295 no-DAC) | ~30 minutes | Multiple times daily |
| Ipamorelin | Short (a few hours) | Daily or several times daily |
| BPC-157 | Short systemic | Often daily (sometimes split) |
| TB-500 | Extended tissue activity | ~Twice weekly |
| Tirzepatide | ~5 days | Weekly |
| CJC-1295 with DAC | ~8 days | Weekly |
| Semaglutide | ~7 days | Weekly |
These are approximate, commonly-cited figures; published pharmacokinetic and label values vary, and this is reference information, not dosing advice.
The DAC example: same peptide, very different half-life
CJC-1295 is the clearest illustration of half-life in action. The base peptide is the same, but the DAC (Drug Affinity Complex) version carries a linker that binds circulating albumin, stretching its half-life to roughly 8 days. The no-DAC version (Modified GRF 1-29) lacks that linker and clears in about 30 minutes. One molecule, two formulations, wildly different dosing schedules — purely because of half-life. See the CJC-1295 reference for the reconstitution math behind both.
Why GLP-1 peptides are weekly
Semaglutide (~7-day half-life) and tirzepatide (~5-day) were engineered for long persistence, which is exactly why they are once-weekly injections: levels stay in range across the whole week and build to a steady state over the first month or two. It is also why they are not "cycled" on and off — see the cycle length guide and the GLP-1 dose calculator.
Half-life is not the same as duration of effect
A common confusion: half-life measures how fast a compound clears, not how long its effect lasts. Tissue-repair peptides can act locally and produce effects that outlast their measurable presence in the blood. Treat half-life as a guide to dosing rhythm, not as a stopwatch on the benefit.
How Peptly fits in
Because the cadence depends on the peptide and your plan, Peptly lets you set your own schedule — from twice daily to weekly — and reminds you when each entry is due (one reminder free; unlimited with Peptly Pro). Each entry you log carries its time, so your actual timing is visible against the plan. For semaglutide and tirzepatide only, Peptly Pro also draws an estimated level chart from your own log and published half-lives, labelled "Estimated, not measured". The app keeps the record; it does not recommend a frequency or an amount.
See also
- Peptide cycle length — on/off basics
- CJC-1295 reference (DAC vs no-DAC)
- Peptide tracker — schedules & reminders
- How to reconstitute peptides
Frequently asked questions
What does half-life mean for a peptide? +
Half-life is the time it takes for half of the peptide to clear your system. After roughly four to five half-lives, most of a dose is gone. It is the main driver of how often a peptide is dosed — a short half-life needs frequent dosing, a long one needs infrequent dosing.
Why is semaglutide dosed weekly but Modified GRF 1-29 several times a day? +
Semaglutide has a half-life around 7 days, so a single weekly injection keeps blood levels steady. Modified GRF 1-29 (CJC-1295 without DAC) clears in roughly 30 minutes, so research protocols dose it far more frequently. The dosing frequency simply follows the half-life.
Does a longer half-life mean a stronger peptide? +
No. Half-life describes how long a peptide lasts in the body, not how potent it is. A long half-life means less frequent dosing and steadier levels — not a bigger effect. Potency and half-life are independent properties.
Is half-life the same as how long the effect lasts? +
Not always. Some peptides — tissue-repair compounds in particular — act locally and their effect can outlast their measurable time in the bloodstream. Half-life is a pharmacokinetic measure of clearance, not a direct measure of how long an effect persists.
Can Peptly remind me on my own schedule? +
Yes. You set the schedule — daily, twice daily, every other day, twice weekly or weekly — and Peptly reminds you when each entry is due (one reminder free; unlimited with Peptly Pro). Each entry you log carries its time, so you can see your actual timing against the plan. Peptly does not recommend a frequency.