GlossaryStacking & CyclingOn-Cycle
Stacking & Cycling

On-Cycle

Also known as: during cycle · active cycle

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

On-cycle is the active window of a protocol: the dates you are dosing, at the doses you planned. It starts with the first dose and ends with the last one. If the protocol includes a titration step, those lower-dose weeks are part of the on-cycle too, even though you have not reached the final dose yet.

Because this is when the drug is in your system, it is also when side effects and lab changes happen, and the response itself can change over the course of the on-cycle. In a 16-week study of twice-daily hexarelin, a growth hormone-releasing peptide, the growth hormone response to a test dose was already significantly lower at week 4 than at the start and was still reduced at week 16. The effect you notice at the end of an on-cycle may not match the effect you noticed in the first weeks.

Why it matters

Most of what you can learn from a protocol is learned on-cycle, so the measurements you take during it matter. Some changes show up in labs before you would feel anything. In a 12-month randomized trial of the oral ghrelin mimetic MK-677 in older adults, fasting blood glucose rose by an average of 0.3 mmol/L (5 mg/dL) and insulin sensitivity decreased, changes you would only catch with bloodwork.

Approved drug labels build monitoring into the active phase as well. The Wegovy (semaglutide) prescribing information tells prescribers to monitor kidney function when starting or increasing the dose in people reporting severe gastrointestinal side effects, because most reported kidney injury cases followed nausea, vomiting, or diarrhea that led to fluid loss. If an approved drug with large trials needs that kind of on-cycle check, a research compound with far less human data deserves at least as much attention.

How to run an on-cycle

  1. Record baseline labs and measurements before the first dose, so on-cycle values have something to be compared with.
  2. Log every dose with the date, time, amount, and injection site, plus any symptoms.
  3. Change one thing at a time. If you adjust the dose, note the date so you can line it up with later changes.
  4. Repeat the same labs partway through and near the end, under the same conditions each time (time of day, fasting or not).
  5. Write down your stop rule before you start: which symptom or lab value ends the on-cycle early.

Common mistakes

  • Skipping baseline labs, which leaves nothing to compare on-cycle results against.
  • Judging the whole cycle by how you felt in the first two weeks.
  • Changing dose, timing, and compounds in the same week, so no change can be traced to a cause.
  • Ignoring lab markers such as fasting glucose because you feel fine.
  • Pushing through severe vomiting or diarrhea without considering fluid loss.

Sources

  1. Clinical trialGrowth hormone status during long-term hexarelin therapy. J Clin Endocrinol Metab, 1998. PMID 9589671.
  2. 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.
  3. Prescribing informationWEGOVY (semaglutide) injection, for subcutaneous use: Prescribing Information. U.S. Food and Drug Administration, 2021.

Page updated . How we grade evidence: methodology.

Related Terms

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.

Cycle

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

Titration

Titration is starting a drug at a low dose and raising it in planned steps, so your body can adjust and side effects stay manageable.

Loading Phase

A loading phase is a period of larger initial dosing meant to reach a target drug level quickly, before switching to a smaller maintenance dose.

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