Cycle

Also known as: protocol cycle · run

A cycle is a planned period of taking a compound followed by a planned break, often repeated over time.

A cycle splits a protocol into an on-cycle phase, when you take the compound, and an off-cycle phase, when you stop. Patterns such as "8 weeks on, 4 weeks off" are often written as if they were rules, but for most research peptides those lengths are community conventions. They did not come from trials comparing one cycle length with another.

The usual rationale is that continuous exposure can blunt the response (receptor desensitization) and that a break lets it recover. That does happen for some compounds. In a 16-week study of twice-daily hexarelin, a growth hormone-releasing peptide, the growth hormone response to a test dose was significantly lower at weeks 4 and 16 than at the start and returned to baseline 4 weeks after stopping. It does not happen for every compound. In a randomized trial of the oral ghrelin mimetic MK-677 in adults aged 60 to 81, daily use raised growth hormone and IGF-1 to young-adult levels over 12 months of treatment.

Why it matters

Whether cycling helps depends on the compound, and for some it is the wrong model entirely. When semaglutide 2.4 mg and lifestyle support were stopped after 68 weeks in the STEP 1 trial extension, participants regained about two-thirds of their prior weight loss within a year, and most cardiometabolic improvements moved back toward baseline. For a drug whose effect depends on ongoing exposure, the off phase is a loss of effect, not a reset.

So "should I cycle this?" has a compound-specific answer. Is there evidence the response fades with continuous use? Does it recover after a break? What happens to the outcome you care about while you are off? For most research peptides, nobody has measured all three, which means any cycle length you choose is a judgment call, not a researched schedule.

How to plan a cycle

Look for direct evidence of tolerance for that specific compound, meaning a measured drop in response with continued use, not a forum rule.
Set the on-cycle length around what you want to measure, and record baseline values before you start.
Make the off-cycle at least 5 half-lives of the longest-acting compound, so the drug is mostly gone before you judge what persists.
Decide in advance what result would make you stop early, extend, or not repeat the cycle.

Fraction eliminated after n half-lives = 1 − 0.5^n

Worked example

A compound with a 5-day half-life is about 97% eliminated after 5 half-lives (1 − 0.5^5 = 0.969), which is 25 days. An off-cycle shorter than that is still measuring a period with drug on board.

Common mistakes

Treating "8 weeks on, 4 weeks off" as a researched rule when it is a convention.
Cycling off a compound whose benefit depends on continued exposure, then being surprised when the benefit fades.
Assuming every peptide causes tolerance because some growth hormone secretagogues have shown it.
Making the off phase shorter than the compound's clearance time, so "off" measurements still reflect drug in your system.
Changing doses or adding compounds mid-cycle without noting it, which makes the cycle impossible to evaluate.

Sources

Clinical trialGrowth hormone status during long-term hexarelin therapy. J Clin Endocrinol Metab, 1998. PMID 9589671.
Clinical trialEffects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med, 2008. PMID 18981485.
Clinical trialWeight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes Obes Metab, 2022. PMID 35441470.

Page updated October 3, 2026. How we grade evidence: methodology.

Related Terms

On-Cycle

On-cycle is the phase of a cycle when you are actively taking a compound, as opposed to the planned break (off-cycle).

Off-Cycle

Off-cycle is the planned break in a cycle when you stop taking a compound, used to let the drug clear and to see which effects last.

Receptor Desensitization

Receptor desensitization is the drop in a cell's response to a drug or hormone after repeated or continuous stimulation of its receptor.

Stack

A stack is two or more compounds used during the same period, usually chosen because they are thought to act through different mechanisms on the same goal.

Look up any peptide term inside DoseCraft Pro

The glossary is just the start. Inside DoseCraft you get 90+ compound deep-dives, a PK-aware protocol engine, interaction checker, and vendor trust scores — every term surfaced in protocol-design context, not a separate page.

Start Free Trial