How Half-Life Shapes Peptide Dosing Schedules

Why half-life sets the schedule

A peptide's half-life is the time it takes for half of a dose to clear from the blood. It decides whether a compound produces a short spike or a level that stays up for days, so two peptides aimed at the same growth hormone (GH) axis can end up on schedules as different as several injections a day versus one a week.

Half-life isn't the whole story, because the hormones people care about (GH, then IGF-1) run on their own timeline. This page looks at how those timelines shape the schedules that trials used and that users report. Dose-response and saturation dosing are covered in our guide to general peptide dosing principles.

Short-acting GH peptides

Ipamorelin is the best-measured example. In a 1999 pharmacokinetic study, 40 healthy men received IV infusions at five dose levels. Ipamorelin had a terminal half-life of about 2 hours. Each dose produced a single burst of GH that peaked at roughly 40 minutes and then fell to negligible levels. One dose, one pulse: that pattern is why community protocols for ipamorelin and GHRPs such as GHRP-2 and GHRP-6 repeat doses through the day instead of relying on a single injection. Our explainer on the growth hormone pathway covers how these compounds act on the pituitary.

Vendor guidance for ipamorelin lists 200-300 mcg per dose, two to three times daily. Many users describe something simpler: one bedtime dose of 100-300 mcg combined with Mod GRF 1-29. For GHRP-2 and GHRP-6, community and vendor guides describe 100-300 mcg per injection, one to three times daily. None of these figures comes from a trial; the human studies gave these compounds intravenously, dosed by body weight.

Mod GRF 1-29 (often sold as "CJC-1295 without DAC") is a modified fragment of growth hormone-releasing hormone (GHRH). Native GHRH lasts only minutes in the blood, the same limitation the CJC-1295 researchers set out to fix. Community guides put Mod GRF 1-29's half-life at about 30 minutes, but we couldn't find a human pharmacokinetic study confirming it. Users commonly report 100-300 mcg with ipamorelin at bedtime, often five days on and two off.

The reason for pairing the two goes back to a 1990 study in 18 healthy men. Low IV doses of a GHRP given together with GHRH released GH synergistically, more than either did alone, which suggested the two act through separate pathways. As of October 2026, no controlled trial has tested the Mod GRF 1-29 plus ipamorelin combination that users actually run.

CJC-1295 with DAC: a half-life measured in days

CJC-1295 with DAC (Drug Affinity Complex) was built to last. The DAC lets the peptide bind to albumin in the blood, which protects it from rapid breakdown. In two 2006 placebo-controlled trials in healthy adults aged 21-61, its estimated half-life was 5.8-8.1 days. After one injection, mean GH rose 2- to 10-fold for six days or more, and IGF-1 rose 1.5- to 3-fold for 9-11 days. With repeated doses, IGF-1 stayed above baseline for up to 28 days.

Those trials used weight-based doses: single injections ranging from 30 to 250 mcg/kg, or two to three doses given weekly or every other week. The authors reported no serious adverse reactions and found tolerability best at 30-60 mcg/kg. Vendor and community guides describe 500-1,000 mcg per week, given as one or two injections; we couldn't trace that range to any study. Either way, a weekly rhythm follows from the half-life.

Pulse vs. bleed: what the human data show

Community guides, including an earlier version of this page, split GH protocols into two camps. The "pulse" approach uses short-acting peptides several times a day to create sharp GH peaks. The "bleed" approach uses CJC-1295 with DAC, on the assumption that a GHRH analog present around the clock flattens GH into a steady, raised level that is weaker than natural pulses.

The one human study that measured this directly found something different. Ionescu and Frohman (2006) sampled blood every 20 minutes overnight in healthy men aged 20-40 before and one week after a single injection of 60 or 90 mcg/kg CJC-1295. GH release stayed pulsatile: the frequency and size of GH pulses didn't change. What changed was the floor between pulses. Trough GH rose about 7.5-fold, which lifted mean GH by 46%, and IGF-1 rose 45%, with similar results at both doses.

So in this study, CJC-1295 with DAC kept the natural pulse pattern and raised the baseline underneath it. The authors suggested the higher trough levels may drive the IGF-1 increase, since IGF-1 didn't correlate with any measure of the pulses themselves.

That doesn't settle which schedule is better. The study was small, followed people for one week after one dose, and measured hormones rather than body composition or recovery. As of October 2026, no trial has compared a pulse protocol with CJC-1295 with DAC on any physical outcome, so claims that one approach builds more muscle rest on reasoning about physiology and on user reports.

Whether months of constant GHRH exposure cause desensitization is also untested in people. The closest long-term data point in this drug class is a 16-week study of twice-daily hexarelin in 12 older adults: the GH response fell by roughly half and recovered within four weeks of stopping. Our page on peptide cycling and desensitization goes into that in more detail.

Timing around sleep and training

Short-acting peptides let users choose when the pulse happens, and most community timing advice tries to line doses up with the body's own GH release.

Sleep. In healthy young men, a pulse around sleep onset is usually the largest daily GH release and sometimes the only one, according to a 2000 review by Van Cauter and Copinschi. GH output tracks slow-wave sleep, while women have more frequent daytime pulses. That research is the basis for the common user practice of a bedtime dose, but no study has tested whether bedtime dosing of ipamorelin or Mod GRF 1-29 gives better results than other times. Hexarelin offers a caution: in a 2004 study of seven young volunteers, four 50 mcg doses given through the night raised GH but reduced deep sleep and raised cortisol.

Training. Exercise and sleep are the strongest natural triggers of GH release. A 2003 review in Sports Medicine reported a significant GH response to resistance training, with the largest responses to endurance exercise above the lactate threshold for at least 10 minutes. Users often add a post-workout dose to build on that response; we found no trial that measured whether it adds anything. Because glucose suppresses GH, community guides also describe dosing on an empty stomach, though the exact fasting windows come from user and vendor guidance rather than studies of these peptides.

CJC-1295 with DAC sidesteps most of this. With a half-life of several days, the hour of injection has little bearing on when GH rises.

Why BPC-157 and TB-500 are scheduled differently

Repair peptides aren't aimed at the GH axis, so pulse timing doesn't apply. Their schedules come mostly from vendor guidance and community habit. As of October 2026, we found no published human half-life for either compound at the doses people use.

BPC-157. Users commonly report 250-500 mcg per day by subcutaneous injection, sometimes split into morning and evening doses, and some report 1-2 mg per day for injuries. No human dose-finding study exists. Many users inject close to the injury on the theory that local concentration matters, but the animal research doesn't test that idea. A 2025 systematic review in HSS Journal found 35 of 36 studies were preclinical, mostly with systemic routes. The often-cited 2003 rat Achilles tendon study gave BPC-157 by intraperitoneal injection far from the tendon and still reported faster healing. No human study has compared injection sites. Some users take oral forms for gut goals, based on rodent data and the peptide's reported stability in gastric juice; that hasn't been tested in people.

The human data are very thin. A 2025 IV safety pilot gave two adults up to 20 mg and reported no adverse events. A placebo-controlled pilot after rotator cuff surgery (NCT07803250, about 30 participants, daily subcutaneous injections for 90 days) is registered to start in January 2027.

TB-500. TB-500 is a seven-amino-acid fragment of thymosin beta-4, not the full 43-amino-acid protein. Vendor guidance describes a "loading" phase of 2-2.5 mg twice weekly for 4-6 weeks, followed by monthly maintenance doses. Users on peptide forums describe wider ranges: 2-5 mg twice weekly is common, and others report 0.5-2 mg daily or every other day. There's nothing to check the loading idea against: as of its April 2026 update, FDA says it has identified no human exposure data for the fragment. Vendor claims that injection site doesn't matter because TB-500 acts "systemically" have no human absorption data behind them either. Animal and cell research on the full protein, which binds actin, doesn't automatically apply to the fragment.

What we still don't know

• Whether any GH secretagogue schedule changes body composition or recovery; the human studies measured hormone levels.
• How CJC-1295 with DAC behaves over months of repeated dosing.
• The human half-lives of Mod GRF 1-29 and the repair peptides at the doses users report.