Peptide cycling means running a compound for a defined number of weeks, then stopping for a defined number of weeks before starting again. The purpose is not tradition or caution for its own sake. It is a response to how specific receptor systems behave under sustained stimulation.
Why Peptide Cycling Exists
Growth hormone secretagogues work by binding a receptor (the GHS-R1a receptor for ghrelin mimetics, the GHRH receptor for sermorelin and CJC-1295) and triggering a pulse of growth hormone from the pituitary. Repeated stimulation of the same receptor produces two adaptations: receptor downregulation, where the cell reduces surface receptor density, and depletion of the readily releasable GH pool inside somatotroph cells.
The result is a fading response. A dose of 200 mcg that produced a strong GH pulse in week 2 may produce a noticeably smaller pulse by week 14. IGF-1, the downstream marker most people track, tends to plateau and then drift back toward baseline. Adding more dose to chase the original response accelerates the same adaptation rather than reversing it.
A structured off period gives receptor density and the pituitary GH reserve time to recover, so the same dose produces a meaningful response when you restart. Peptides that do not act through a feedback-regulated endocrine axis, such as local repair peptides, generally do not have this problem.
Which Peptides Actually Need Cycling
Sorting compounds by mechanism is more useful than applying one blanket rule:
- Cycle required: ghrelin mimetics and GH secretagogues (ipamorelin, hexarelin, GHRP-2, GHRP-6, MK-677). These directly downregulate GHS-R1a under continuous exposure.
- Cycle recommended: GHRH analogs (sermorelin, CJC-1295, tesamorelin). Desensitization is slower than with ghrelin mimetics, but pulse amplitude still declines over long uninterrupted runs.
- Cycle by course, not by receptor: repair peptides (BPC-157, TB-500). These are run for the duration of an injury or recovery phase, typically 4 to 8 weeks, then stopped because the goal is met, not because a receptor is fatigued.
- Dose-limited rather than cycled: GLP-1 class compounds (semaglutide, tirzepatide, retatrutide). These are titrated up and held, and interruption is driven by side effects or goal completion rather than receptor rescue.
- Fixed protocol courses: longevity peptides such as epithalon, which is conventionally run as a 10 to 20 day course two to three times per year rather than continuously.
The mechanism differences matter for planning. If you are running a GHRH analog alongside a ghrelin mimetic, as in the ipamorelin and CJC-1295 stack, the ghrelin side of the stack is the one that sets your cycle length.
Common Cycle Lengths and Off Periods
These ranges reflect what is used in practice and what the GH secretagogue literature suggests about desensitization timelines. They are starting points, not prescriptions.
- Ipamorelin: 8 to 12 weeks on at 200 to 300 mcg per dose, followed by 4 weeks off. Ipamorelin is the most selective of the ghrelin mimetics and tolerates the longer end of that range better than hexarelin.
- Hexarelin: 4 to 6 weeks on at 100 mcg per dose, followed by 4 to 8 weeks off. Hexarelin desensitizes fastest of the common secretagogues, which is why its on period is the shortest.
- GHRP-2 and GHRP-6: 8 to 12 weeks on at 100 to 300 mcg per dose, followed by 4 weeks off.
- CJC-1295 without DAC: 12 weeks on at 100 mcg per dose, followed by 4 weeks off. The no-DAC version has a short half-life and preserves pulsatility better than the DAC version.
- Sermorelin: 12 weeks on at 200 to 500 mcg nightly, followed by 4 weeks off.
- MK-677: 8 to 12 weeks on at 10 to 25 mg oral daily, followed by 4 or more weeks off. Because it is oral and long acting, exposure is continuous rather than pulsed, which makes the off period more important, not less.
- BPC-157: 4 to 8 weeks at 250 to 500 mcg daily for a specific injury, then stop.
The rough heuristic behind most of these: an off period of at least one third the length of the on period, with 4 weeks as the practical floor. A 12 week run followed by 4 weeks off puts you at three cycles per year with time to reassess between each.
Building a Cycle That Fits Your Goal
Cycle length should be set by what you are trying to measure, not by a calendar habit. Body composition and IGF-1 changes from a GH secretagogue take 8 to 12 weeks to read clearly, which is exactly why that range became the default. A 4 week run is too short to distinguish signal from noise. A 20 week run buries the useful signal under desensitization.
Practical structure for a first GH secretagogue cycle:
- Weeks 0: baseline IGF-1 draw, weight, waist measurement, and a sleep quality note.
- Weeks 1 to 2: start at the low end of the dose range (ipamorelin 200 mcg) to confirm tolerance before adjusting.
- Weeks 3 to 10: hold a steady dose. Do not change two variables at once.
- Week 8 to 10: repeat IGF-1 draw while still on cycle, which is the only window that shows the actual effect.
- Weeks 11 to 12: taper or finish, then begin the 4 week off period.
- Off weeks 1 to 4: no secretagogues. Repair peptides and non-endocrine compounds can continue if there is a reason for them.
Keep the dose fixed within a cycle so the data means something. Use the reconstitution calculator to lock in the unit count for your specific vial and BAC water volume, then draw the same number of units every time. Changing the concentration mid-cycle is the fastest way to make your own results uninterpretable.
Tracking and Restarting
IGF-1 is the standard proxy for GH secretagogue response because GH itself is pulsatile and a single random draw tells you almost nothing. Draw at baseline, again at week 8 to 10 on cycle, and optionally at the end of the off period to confirm you have returned near baseline before restarting.
When you restart, go back to the dose that worked at the start of the previous cycle rather than the highest dose you reached. If the response at the restart dose is clearly weaker than it was on the first cycle, the off period was too short. Extend the next one to 6 or 8 weeks before concluding the compound has stopped working for you.
One more practical note: a vial of reconstituted peptide will not survive a 4 week off period plus a full cycle. Plan vial sizes around your on weeks so you are not storing a partially used vial past its stable window.