PC-ART-006 Reference 22 August 2026 7 min read

The intervals have no trial behind them

Eight to twelve weeks on, four to six weeks off. You will see that schedule everywhere growth hormone secretagogues are discussed, quoted with total confidence, and here is the remarkable part: no clinical study of any of these compounds has tested it. None has compared cycled dosing with continuous dosing at all. The longest controlled human data on a ghrelin-receptor secretagogue ran continuously rather than cyclically, and reported sustained effects rather than a fade.

The four-to-eight-week figure attached to repair peptides has the same footing. There is no controlled human trial of BPC-157 or TB-500 for tissue repair at any duration, so there is no human evidence a duration could be derived from. The FDA's own record puts the gap plainly: for BPC-157 it has identified no, or only limited, safety-related information.

One washout figure is real, and it deserves separating from the rest. CJC-1295 with the drug affinity complex has an estimated half-life of 5.8 to 8.1 days, measured in phase I trials, so a longer interval after it is a straightforward pharmacokinetic consequence. That is a number with a study behind it. The schedule around it is not.

Desensitisation was measured under a different exposure

The mechanism behind cycling is receptor desensitisation, and it is real — which is exactly why this is worth pulling apart carefully rather than dismissing. Continuous intravenous infusion of GHRP-6 over 34 hours in nine healthy men produced measurable homologous desensitisation, a blunted response to a further bolus. Desensitisation of G protein-coupled receptors under sustained agonist exposure is well described in general, and the growth hormone secretagogue receptor is one of them.

What it does not establish is the situation anyone is actually in. Thirty-four hours of continuous infusion is a fundamentally different exposure from an intermittent subcutaneous injection with many half-lives of gap between doses. Intermittent dosing at intervals long relative to the half-life is precisely the pattern that avoids sustained occupancy — and no study measures desensitisation under it for these compounds. Nor does any study measure how long a receptor population takes to recover, which is the one number a washout interval would need.

So: the mechanism is real, its relevance to an intermittent protocol is untested, and the specific intervals are invented. Read that as a gap in the evidence rather than a verdict against cycling. The record simply does not contain the study that would settle it either way, and saying so is more useful than picking a number.

The approved label monitors rather than cycles

One compound in this area is approved and dosed under a label, and what that label does instead of cycling is the most useful thing on this page. Tesamorelin is approved for continuous daily dosing, with no cycling anywhere in its labelling. What it carries is an instruction to monitor IGF-1 and to consider discontinuation at persistent elevations beyond three standard deviation scores — with 47% of patients recording an elevated level.

The label also names the effects that genuinely accumulate under sustained growth hormone elevation, which are the ones a break would be for. Fluid retention, arthralgia and carpal-tunnel-like paraesthesia are the best established, appearing both in the label and in a systematic review of growth hormone use in healthy elderly people. Glucose intolerance is the other: recipients were somewhat more likely to develop diabetes and impaired fasting glucose, and the tesamorelin label carries a section on it.

Notice the substitution, because it is the whole argument in one line. A stopping rule that exists is a laboratory value with a threshold and a decision attached to it. A stopping rule that does not exist is a calendar interval. They get presented as the same kind of thing and they are not.

One more claim runs against the evidence rather than with it. Stepping away from a protocol is usually described as costing nothing. No study has measured retention of body composition or symptom benefit after discontinuing any of these compounds, and the growth hormone literature leans the other way — the body-composition changes in that review were observed during treatment.

• IGF-1

  The biomarker with a real threshold behind it. The approved label instructs monitoring and names persistent elevation above three standard deviation scores as grounds to consider discontinuation. That is the closest thing to a published stopping rule in this area.

• Fasting glucose and insulin

  Growth hormone induces insulin resistance, and the approved label carries a glucose intolerance section. Drift here is measurable, unlike the subjective indicators usually listed beside it.

• Fluid, joints and nerves

  Oedema, arthralgia and carpal-tunnel symptoms are the classic consequences of growth hormone excess and appear in both the label and the systematic review. They are observations a person can make, and unlike receptor fatigue they have been counted.

Two things the record does say clearly

Two facts here are solid, and they are better things to carry away than any interval.

The first: mechanism does not travel across a class. GHRH analogues and ghrelin-receptor secretagogues act at different receptors on different cells, and flattening them into one row is what makes a single shared cycling rule look reasonable in the first place. Wherever the two are described together, a rule derived from one is being applied to the other with nothing to justify it.

The second is arithmetic, and it touches every dose whatever the schedule. A lyophilised peptide solid is typically 70 to 90% peptide by weight, the balance counter-ion and bound water. Reconstitution maths uses the labelled mass, so what actually gets delivered is lower than the calculated figure by somewhere between a tenth and a third. That is a larger and far more certain effect than anything a cycle length is being asked to control.

Homologous desensitisation

Reduced response to a further dose of the same agonist after sustained exposure. Measured for GHRP-6 under continuous intravenous infusion; not measured under intermittent injection.

GHS-R1a

The growth hormone secretagogue receptor, also the ghrelin receptor. The target of ipamorelin and the GHRPs — a different receptor from the GHRH receptor.

Washout

An interval intended to clear a compound before dosing resumes. For CJC-1295 with DAC the pharmacokinetics give a real basis; for the rest, no interval has been studied.

IGF-1

Insulin-like growth factor 1, the downstream marker of growth hormone action, and the only biomarker in this area with a published threshold attached to a decision.

Peptide content

The share of a lyophilised solid that is peptide rather than salt or water, typically 70 to 90%. The gap between labelled mass and delivered peptide.

Not on file

Used here to mean no record exists, as distinct from a value of zero or a figure nobody has looked for. Most cycling intervals fall into this category.

Sources and evidence