Nearly every community protocol for growth-hormone peptides repeats the same rule: run it 8 weeks on, then take 8 weeks off, or the pituitary will desensitize and the peptide will stop working. It is treated as settled fact. The clinical literature does not settle it that way.
The single most-studied GHRH peptide, tesamorelin, was dosed every day for 52 continuous weeks in its Phase 3 program and kept working the entire time. Meanwhile the peptide that desensitizes most clearly — hexarelin — loses most of its effect in about two weeks, far faster than any 8-week cycle would catch. The "cycle to avoid desensitization" rule is too blunt to describe either case. What actually determines whether a GH peptide loses its punch is not the calendar. It is which receptor the peptide hits and whether it preserves the body's natural pulse.
Research-context information only. The compounds discussed below are research peptides; some are also the active ingredients in FDA-approved products. Protocols, doses, and reactions reported here come from published research and self-reported community sources. This article reports what has been documented, not what should be done. Consult a licensed physician for personal medical decisions.
The real variable: pulsatility, not weeks on the calendar
Growth hormone is not secreted continuously. The healthy pituitary releases it in discrete pulses — the largest during deep sleep — with quiet troughs in between. That pulsatile pattern is not incidental; it is how the downstream signaling is meant to work, and continuous GH exposure produces different effects than pulsatile exposure.
Both peptide families act on G-protein-coupled receptors, and the general rule for that receptor class is that continuous agonist occupancy drives the receptor to internalize and downregulate, while transient, intermittent stimulation does not. So the question for any GH peptide is mechanical: does this molecule deliver a brief pulse that clears and lets the receptor reset, or does it bathe the receptor in continuous stimulation? Half-life answers most of it.
That single distinction — pulse-preserving versus continuous — explains the trial data far better than "weeks on the calendar" does, and it splits cleanly along the two receptors these peptides use.
GHRH-receptor analogs: a short half-life preserves the pulse
Sermorelin, tesamorelin, and modified GRF 1-29 (the peptide sold as "CJC-1295 without DAC") all act on the GHRH receptor and all clear quickly — sermorelin's half-life is roughly 10 to 20 minutes, tesamorelin's around 25 to 40 minutes. Each injection produces one transient GHRH pulse that is gone well before the next dose. Daily injection, in other words, is not continuous receptor occupancy. The somatotroph still gets its downtime, and the natural rhythm is preserved.
The trial record reflects this. In a 16-week study of nightly GHRH-(1-29) in adults aged 55 to 71, integrated growth-hormone output rose roughly 107% in men and 70% in women and stayed elevated across the full treatment period, with IGF-1 rising and remaining above baseline — no sign of the pituitary desensitizing to nightly stimulation over those 16 weeks (Khorram et al., 1997). Tesamorelin goes further: in its Phase 3 program it was given at 2 mg daily for 52 continuous weeks, IGF-1 reached its plateau by week 26 and was maintained at that level through week 52, and visceral-fat reduction held across the full year with the trials reporting no tachyphylaxis (Falutz et al., 2007; long-term data). The FDA-approved protocol for tesamorelin is, accordingly, continuous daily dosing with no cycling.
The one GHRH analog where continuous stimulation is mechanistically plausible is CJC-1295 with DAC. The DAC modification binds it to albumin and stretches its half-life to roughly six to eight days, producing near-continuous GHRH signaling — a "GH bleed" rather than a pulse. That is exactly the continuous-occupancy pattern that could desensitize the receptor over time. Interestingly, even here one study found that GH pulsatility was largely preserved during continuous CJC-1295 stimulation (Teichman et al., 2006), and no long-term human trial has tested whether extended DAC use blunts the axis. So the long-acting form is the one peptide in this group where a cautious, monitor-IGF-1 approach is defensible — and notably, it is the form community protocols built the cycling rule around.
GHRPs: the ghrelin receptor is where desensitization is real
The GHRPs — ipamorelin, GHRP-2, GHRP-6, and hexarelin — are a different mechanism entirely. They act on the ghrelin receptor (GHS-R1a), and this is where receptor downregulation with prolonged stimulation is genuinely documented. But it follows a gradient, not a blanket rule.
Hexarelin sits at the severe end. Daily dosing studies documented the GH response falling roughly 60% within two weeks, and over 16 weeks of continuous use the same dose that initially raised GH by around 800% produced only about 120% above baseline by the end — clear, dose-limiting tachyphylaxis driven by ghrelin-receptor internalization, and reversible after a washout (hexarelin desensitization study). GHRP-2 and GHRP-6 show some attenuation with prolonged continuous use but markedly less than hexarelin. Ipamorelin is the most spared: in preclinical work it maintained its GH-releasing effect across repeated dosing without tachyphylaxis (Raun et al., 1998), though that work ran on short timescales and no long-term human trial has quantified it.
So for the GHRPs, cycling logic has real mechanistic backing — strongest for hexarelin, weakest for ipamorelin. The mistake is not the cycling instinct itself; it is exporting that instinct wholesale onto the GHRH analogs, which use a different receptor and behave differently.
So where did "8 weeks on, 8 weeks off" come from?
If the trial evidence doesn't require an 8/8 cycle for most of these peptides, why is it the near-universal community default? Several threads feed it, and most have nothing to do with GHRH-receptor desensitization:
- Conflation across the two receptors. People run GHRH + GHRP stacks and apply the ghrelin-receptor cycling logic — which is legitimate for hexarelin — to the whole stack, including the GHRH half that doesn't need it.
- Carryover from steroid culture. "Cycle everything" is the default mental model from anabolic-steroid and exogenous growth-hormone use, where the rationale (suppression of the body's own axis) is real but does not transfer to a secretagogue acting on an intact pituitary.
- IGF-1 hedging. A lot of the "give the axis a rest" instinct is really a hedge against keeping IGF-1 elevated indefinitely — a safety-margin argument, not a receptor-desensitization argument. The two get blurred.
- Cost. Eight weeks off is eight weeks of vials not bought. For many users that is the honest primary driver, with desensitization offered as the after-the-fact rationale.
None of these are unreasonable reasons to cycle. They are simply different from "the peptide will stop working," which is the claim the trial data does not support for the short-acting GHRH analogs.
What the evidence supports, peptide by peptide
| Peptide | Receptor | Desensitization with continuous use | What the evidence supports |
|---|---|---|---|
| Sermorelin | GHRH | Not seen over 16 weeks of nightly dosing | Cycled or continuous both documented; cycling mainly cost/IGF-1 driven |
| Tesamorelin | GHRH | None over 52 weeks (FDA protocol is continuous) | Continuous use is the trial-validated path |
| Modified GRF 1-29 (CJC-1295 no-DAC) | GHRH | No long-term human data; short half-life preserves pulse | Cycling is community convention, not desensitization-proven |
| CJC-1295 with DAC | GHRH | Theoretical (continuous "GH bleed"); untested long-term | Monitor IGF-1; cautious cycling defensible |
| Ipamorelin | Ghrelin | Minimal in preclinical work; no long-term human data | Least desensitizing GHRP; cycling is convention |
| GHRP-2 / GHRP-6 | Ghrelin | Some attenuation with prolonged use | Cycling has partial mechanistic backing |
| Hexarelin | Ghrelin | Documented and rapid (~60% by 2 weeks) | Cycling genuinely warranted; short cycles only |
The short version: the calendar is the wrong unit. Match the approach to the receptor. Short-acting GHRH analogs preserve the pulse and have trial support for continuous use; ghrelin-receptor peptides desensitize on a gradient that peaks with hexarelin; and the long-acting DAC form is the one GHRH peptide where continuous stimulation warrants caution.