Peptide Cycling in Bodybuilding: Hard Cycles vs. Pulsing

Two ways lifters schedule GH peptides

Most cycling talk in bodybuilding is about growth hormone (GH) secretagogues. That means GHRH analogs such as CJC-1295 and Mod GRF 1-29, plus GHRPs such as ipamorelin and hexarelin. Users widely report that these compounds seem to work less well after weeks of daily use, and the usual explanation is desensitization of the GH-releasing cells in the pituitary.

The two camps agree on that worry and disagree on the fix. One runs a defined block of daily use and then stops completely for weeks. The other keeps going for months but builds in short, regular breaks, most often 5 days on and 2 days off. No trial has tested either schedule against the other, so this page checks each side's claims against the few human studies that tracked GH response over time. Why peptide classes behave differently at the receptor is covered in our page on the receptor science behind peptide cycling.

The hard on/off cycle

The hard cycle is the older bodybuilding model, borrowed from how lifters plan steroid cycles. A user picks a phase such as contest prep and runs the peptides daily until it ends. Community guides commonly describe on-blocks of 8-16 weeks for GHRH and GHRP combinations. Forum guides also repeat a rule of thumb that the off period should be at least half as long as the on period, and ideally equal. We couldn't trace that rule to any study.

Durations listed for single compounds come from vendors and users, not trials. Vendor and community guidance lists 8-12 weeks for ipamorelin and for GHRP-6, 8-16 weeks for GHRP-2, and 12-16 weeks for CJC-1295. Hexarelin gets the shortest cycle. A common community pattern is 4-8 weeks on, followed by a break of about the same length. In a 2018 thread on one bodybuilding forum, a user summed up the reasoning: people desensitize to hexarelin "pretty quick, I think like 4 weeks roughly."

The claim behind this approach is that desensitization builds steadily with daily use. On that view, a short weekly break can't undo it, and only a full stop of several weeks lets the pituitary recover.

The pulse schedule

The pulse approach treats GH peptides as a long-term routine rather than a phase. The version users describe most often pairs Mod GRF 1-29 (CJC-1295 without DAC) with ipamorelin, each at about 100-300 mcg by subcutaneous injection at bedtime. Many run it 5 days on and 2 days off for many months. People who prefer it usually say they want steady effects on sleep and recovery, not a peak for one event.

Proponents say two days off each week keep sensitivity from sliding, so a long break is never needed. Some argue that even the off days are optional and point to the long MK-677 trial described below.

A related forum claim concerns CJC-1295 with DAC, which stays active for about a week. Community copy, including an earlier version of this page, said it produces a constant "bleed" of GH that flattens natural pulses. The one human study that measured this found otherwise (see below).

What human studies show about desensitization

Only a handful of human studies followed the GH response to these compounds for more than a few days. They are small and mostly enrolled older adults or children. None used the doses or combinations common in bodybuilding.

Hexarelin: a partial drop that reversed

The study cited most often gave 12 healthy older adults subcutaneous hexarelin twice daily for 16 weeks. The GH response, measured as the area under the GH curve after a dose, fell from 19.1 to 13.1 µg/L per hour after one week. It reached 12.3 at week 4 and 10.5 at week 16, a drop of about 45%. Four weeks after stopping, a fresh dose produced 19.4, no different from the start. The authors called the loss "partial and reversible."

A 1996 study in seven short children taking intranasal hexarelin three times daily showed a similar shape. The GH peak after a test dose roughly halved within 7 days, then held steady for 6 months. The children's growth rate still rose, from 5.3 to 7.4 cm a year. Three months after stopping, the GH response had partly recovered.

In both studies most of the drop came in the first week, faster than either schedule assumes. The response then leveled off instead of sliding toward zero.

Constant GHRH and GHRP-2 exposure

Studies of natural GHRH show both sides. In a 1986 study, a 6-hour GHRH infusion in 10 healthy men left the pituitary partly refractory to a further large GHRH dose. It still responded fully to a different stimulus, insulin-induced low blood sugar. When the same research group infused GHRH continuously for 14 days in five healthy men, GH pulses were preserved and IGF-1 roughly doubled. The response to a large test dose wasn't reduced, and the authors concluded the pituitary cells "remain responsive to prolonged constant stimulation."

A small 2001 study found the same for a GHRP. Ten older adults with low GH secretion received GHRP-2 by continuous subcutaneous infusion for 30 days. Pulsatile GH secretion and IGF-1 rose within 24 hours and stayed raised for the whole month. Continuous exposure, the thing both cycling camps try to avoid, didn't produce lasting tolerance in these short studies.

CJC-1295 with DAC and the "bleed" claim

In a 2006 study, healthy men aged 20-40 received one injection of CJC-1295 (60 or 90 mcg/kg). A week later, the number and size of GH pulses were unchanged. What rose was the level between pulses: trough GH went up 7.5-fold, lifting mean GH by 46% and IGF-1 by 45%. So the long-acting form raised the floor under normal pulses rather than replacing them with a flat line. The study looked at a single dose over one week, so it can't show what months of weekly dosing do. Our page on how half-life shapes dosing schedules covers the pulse versus bleed question in more detail.

MK-677 over two years

The longest data come from a 2-year randomized trial of oral MK-677 (ibutamoren), 25 mg once daily, in 65 healthy adults aged 60-81. GH and IGF-1 rose to levels typical of young adults, and the authors' 2-year exploratory analysis confirmed the 1-year results. Fat-free mass rose about 1.1 kg while the placebo group lost a little, though strength and function didn't change. Daily use with no break didn't erase the IGF-1 effect in this trial.

It did raise fasting glucose by about 5 mg/dL and lower insulin sensitivity. That's a different reason to take breaks, unrelated to receptor tolerance. Our page on long-term peptide use looks at that side of the question.

How the evidence fits each schedule

Neither philosophy comes out cleanly. The hexarelin data back the hard-cycle claim that the loss of response is real and that about four weeks off restored it. They don't back the idea that the loss keeps growing until the peptide stops working. The response settled at a little over half of baseline, and growth in the children kept improving.

For the pulse schedule, no study has tested whether two days off per week restores anything. Because most of the hexarelin drop came within 7 days, a weekend break may be too short to reset it, though that's an inference. The constant-exposure studies and the MK-677 trial suggest some compounds produce little desensitization to begin with, which would make the weekly break matter less than users assume.

The compounds also differ from one another. Hexarelin showed the clearest tolerance, while GHRH and MK-677 showed the least. As of October 2026, ipamorelin, the GHRP most often used on pulse schedules, has no long-term human study of GH response. Its human data are one IV dosing study and a failed Phase 2 trial in postoperative ileus. Applying one rule to every secretagogue, as many forum guides do, goes beyond the evidence.

Fading effects in user reports may have other causes. Early water retention settles, and gray-market products vary in content. No study has separated these from receptor tolerance.

Recovery peptides sit outside this debate

The on/off versus pulse question is mostly about the GH axis. For BPC-157 and TB-500, vendor and community guidance describes a single course instead: 4-12 weeks for BPC-157, and for TB-500 a 4-6 week loading phase followed by monthly doses. No human study has tested any duration for either. IGF-1 LR3 is commonly run in 4-6 week blocks, which users attribute to receptor downregulation that hasn't been measured for this analog. Plans built around a specific goal are covered in cycling protocols by goal.

What we still don't know

• No trial has compared a hard cycle with a 5-on/2-off schedule, or either with continuous daily use.
• There are no long-term human data on GH response to ipamorelin or Mod GRF 1-29 at the doses lifters report.
• None of the desensitization studies enrolled young, trained adults.
• Whether two days off per week restores any lost response has never been measured.
• The off-period rule of thumb (at least half the on period) has no traceable source.