Peptide cycling

The practice of using a peptide for a defined period followed by a break — to avoid receptor desensitisation, tachyphylaxis, or other adaptive responses.

Why it matters

Many peptides produce tolerance with continued use. GHRH analogues downregulate pituitary GHRH receptors over weeks of continuous use. Melanocortin agonists similarly produce receptor adaptation. Cycling protocols typically use 8–12 week on cycles followed by 4–8 week off periods.

In practice

Cycling is empirical rather than evidence-based for most peptides — the protocols evolved from anabolic steroid practice and are applied by analogy. Effects of cycling vs continuous use on outcome have not been rigorously studied for most research peptides.

Common confusion

“Cycling solves the tolerance problem” overstates the case — for some peptides the receptor adaptation persists beyond the off-cycle window.

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