Measured half-lives for tesamorelin, BPC-157, TB-500, PT-141, cagrilintide, NAD+ and others, each beside the schedule its label or trials used, with sources.
"How often to inject peptides" has no single answer, and most pages that give one are answering a different question. A half-life says how quickly a molecule leaves the blood; a dosing schedule says how often a dose is given. For the few compounds with a label, the regulator-reviewed schedule sometimes follows the half-life and sometimes ignores it. For the rest there is no label, and often no human half-life at all. This page puts the measured half-lives beside the schedules that exist, with the source of each, and marks where the number is missing.
The GLP-1 medicines have their own pages — tirzepatide's half-life, retatrutide's, and every label side by side on the GLP-1 dosage chart — so they are left out of the table below.
The table
| Compound |
Measured half-life |
Route and who |
Source |
Schedule with a source behind it |
| Sermorelin (GHRH 1-29) |
4.3 min |
IV infusion, 10 healthy men |
JCEM 1994, PMID 7962295 |
None current; no label is in force |
| Tesamorelin |
8 min (SV) · 11 min (WR) |
Under the skin, healthy adults |
EGRIFTA labels, 2026-07-29 |
Once daily (label) |
| Glutathione |
14.1 min |
IV, 10 healthy volunteers |
Eur J Clin Invest 1991, PMID 1907548 |
None (no approved injection) |
| BPC-157 |
under 30 min |
IV and IM, rats and dogs |
Front Pharmacol 2022, PMID 36588717 |
None; no human data |
| Thymosin beta-4 (TB-500's parent) |
0.5–2.08 h |
IV, 54 healthy adults (recombinant) |
J Cell Mol Med 2021, PMID 34346165 |
Once daily for 10 days in that study |
| Ipamorelin |
2 h |
IV, healthy men |
Pharm Res 1999, PMID 10496658 |
None; two IV surgical trials only |
| Bremelanotide (PT-141) |
2.7 h (1.9–4.0) |
Under the skin |
VYLEESI label, 2025-11-13 |
As needed; ≤1 in 24 h; ≤8 a month (label) |
| CJC-1295 with DAC |
5.8–8.1 days |
Under the skin, healthy adults |
JCEM 2006, PMID 16352683 |
Weekly or every two weeks in that study |
| Cagrilintide |
159–195 h |
Under the skin, weekly, adults with overweight |
Lancet 2021, PMID 33894838 |
Once weekly in that trial |
| Semax |
not measured in people |
— |
4 of 208 PubMed records touch PK; none human |
None |
| NAD+ |
not measured as a half-life |
IV infusion, pilot |
Front Aging Neurosci 2019, PMID 31572171 |
None (no approved injection) |
Two cautions about reading across the rows. An intravenous half-life excludes absorption from under the skin, which stretches the curve, so the IV figures are not what a subcutaneous injection produces. And "CJC-1295" in a research vial is usually the form without the drug affinity complex, whose half-life is minutes, not the DAC form measured in 2006; the CJC-1295 dosage page sets out the difference.
Half-life is not the schedule: three cases
Tesamorelin — minutes in the blood, once a day on the label. EGRIFTA SV's half-life of 8 minutes means that a day contains about 180 half-lives; by arithmetic, nothing of a dose is left long before the next one. Both EGRIFTA labels still set one injection daily. The drug's job is to trigger growth-hormone release, and the IGF-1 that follows lasts far longer than the peptide. The label's schedule tracks the effect.
Bremelanotide — hours in the blood, no fixed schedule. VYLEESI's 2.7-hour half-life would fit several doses a day, and its label allows none of that: one dose as needed, at least 45 minutes before the activity it is for, never more than one in 24 hours, and more than eight a month "is not recommended". Here the limit is set by side effects and the trial design, not by clearance.
Cagrilintide — a week in the blood, once a week. At 159 to 195 hours, about half of each weekly dose is still present at the next one, so the level builds to roughly twice a single dose before levelling off (arithmetic by this site). This is the one row where half-life and schedule line up the way the search expects, and it is the same pattern as the weekly GLP-1 medicines.
What the arithmetic says about a missing number
For a compound with a half-life of minutes, the frequency of injection cannot keep a steady level in the blood at any practical schedule; a twice-daily schedule for BPC-157 would still leave about two dozen half-lives between doses, even taking the rat figure at its longest. So a frequency attached to such a compound is a claim about how long its effect lasts. For BPC-157, TB-500 and Semax no human study has measured that effect's duration either, which is why this page reports no schedule for them: none exists with a source.
The frequencies that do circulate for those compounds — once or twice daily, five days on and two off, courses of weeks — are taken from vendor and clinic pages. They are reported on each compound's own page as what circulates, attributed and dated: BPC-157, TB-500, Semax, NAD+, PT-141, tesamorelin, ipamorelin, sermorelin and cagrilintide.
Frequency changes the volume, not the arithmetic
A schedule split into more injections puts less in each one. Units on a U-100 syringe = dose in mg ÷ concentration in mg/mL × 100, so at 2 mg/mL a 500 mcg amount is 25 units and the same 500 mcg split into two injections is 12.5 units each. The vial's concentration, not the schedule, sets how many units carry a given amount; the mg to units page has the tables, and the reconstitution calculator works any vial.
What is not established
Nine of the eleven compounds have no labelled schedule; three have no human half-life at all (BPC-157, TB-500 as sold, Semax); for NAD+ the one human infusion study measured disappearance rather than a half-life. The human figures that exist are mostly single studies of 10 to 54 people, several intravenous, several decades old. Nothing on this page is a frequency to follow; for the labelled products the label governs, and for the rest there is no validated schedule.
Sources and dates
Opened 2026-09-25: the EGRIFTA SV and EGRIFTA WR labels (Theratechnologies, openFDA, effective 2026-07-29) and the VYLEESI label (Cosette Pharmaceuticals, openFDA, effective 2025-11-13), sections 2 and 12.3; abstracts via NCBI E-utilities for PMIDs 7962295, 10496658, 16352683, 33894838, 36588717, 20536472, 1907548, 31572171 and 15344653; the full text of Wang et al. 2021 (PMC8419156, Table 4 and discussion); the PubMed Semax search described above. Half-lives-per-interval and accumulation figures are arithmetic by this site. Corrections go to the contact page.
