Peptide Dosing Frequency: Half-Lives Against Schedules

"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

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, GHRP-6 (measured at 2.5 hours after an intravenous dose), 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. For a weekly medicine the split also reshapes the blood level, which the tirzepatide twice-weekly page models. 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. How long each compound was given in its labels and trials, as against the circulating cycle figures, is tabulated on the peptide cycle length page. The full BPC-157 record, every route and dose from the rat and dog study with the arithmetic of a sub-30-minute half-life, is on BPC-157 half-life.

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.