Peptide Cycling Schedules Compared: What the Evidence Shows

Why lifters cycle peptides

Most cycling advice for growth hormone (GH) peptides rests on one idea: stimulate a receptor often enough and it stops responding as well. Forum guides call this receptor downregulation and build their on/off schedules around it. The idea is reasonable, and pituitary desensitization has been measured in people. What the guides skip is how big the effect is and how fast it reverses.

Two receptor systems are involved. GHRH analogs such as CJC-1295, tesamorelin and sermorelin act on the receptor for growth hormone releasing hormone. GHRPs such as GHRP-2, GHRP-6, hexarelin and ipamorelin act on the ghrelin receptor. An earlier version of this page put all of them on the ghrelin receptor, which was wrong. Our overview of peptide cycling strategies covers the general case for cycling; this page compares the schedules against the human data.

What human studies show about fading response

As of October 2026, no trial has compared one cycling schedule with another. What exists are studies that gave a GH-releasing compound repeatedly and checked whether the response held up. The response shrinks somewhat but doesn't disappear, and in the one study that tested a break, it came back.

• GHRH, over hours. In 10 healthy men, a 6-hour GHRH infusion left the pituitary partly unresponsive to a follow-up GHRH dose, while its response to a different trigger was larger, so it hadn't run out of GH. The authors called this partial desensitization (Vance, 1986).
• GHRP-2, over 30 days. In 17 healthy older adults given GHRP-2 by continuous infusion under the skin, GH secretion was more than 3 times the saline level on day 1 and still about 1.8 times higher on days 14 and 30. IGF-1 held at a plateau (Bowers, 2004). That's a smaller response, not a pituitary that has stopped listening.
• Hexarelin, over 16 weeks. In 12 healthy older adults injecting hexarelin twice daily, the GH response had fallen about 45% by week 16. Four weeks after stopping, it was back to baseline (Rahim and Shalet, 1998). It's the only human test of an "off" period we found.
• MK-677, over 2 years. MK-677 (ibutamoren) is an oral drug, not a peptide, but it acts on the ghrelin receptor. At 25 mg daily in 65 adults aged 60-81, GH and IGF-1 stayed in the young-adult range through the first year. Fat-free mass rose about 1.1 kg, strength didn't change, and insulin sensitivity fell (Nass, 2008).
• Tesamorelin, over 52 weeks. In HIV-associated lipodystrophy, daily tesamorelin cut visceral fat about 18%, and the cut held over 52 weeks of continuous use. People switched to placebo regained the fat (Falutz, 2008).

The tesamorelin result matters most here, because it's a prescription medicine with controlled long-term data. Continuous use kept working for a year, and stopping reversed the benefit. Strong downregulation would predict the opposite.

Common schedules compared

These schedules come from forum guides and user reports. None has been tested in a trial, so the right-hand column gives the nearest human data.

"Blast and cruise" is borrowed from anabolic steroid culture. One forum-style example for the no-DAC form of CJC-1295 (Mod GRF 1-29) plus ipamorelin describes 100 mcg twice a day for 12 weeks, then 100 mcg once at bedtime with no set end date. That's a community protocol, not a tested one. Its biggest unknown is what months of raised GH and IGF-1 do to blood sugar, a cost the MK-677 trial suggests is real. Our article on long-term effects of peptide cycling looks at that question.

Users on 5-on/2-off schedules often say the weekend gives their receptors a break. Nobody has measured how much sensitivity returns in two days; the hexarelin study only checked recovery at four weeks.

CJC-1295 with DAC and the "GH bleed" claim

The earlier version of this page said CJC-1295 with DAC (drug affinity complex) causes a constant "bleed" of GH that makes cycling tricky and speeds up downregulation. The human data don't support that. The DAC binds the peptide to albumin, giving it a half-life of about 6-8 days. In two placebo-controlled trials in healthy adults, one injection raised mean GH 2- to 10-fold for 6 days or more, and after repeat doses IGF-1 stayed above baseline for up to 28 days (Teichman, 2006).

When researchers sampled blood every 20 minutes overnight a week after a dose, GH pulses kept their normal frequency and size. Trough GH between pulses rose about 7.5-fold (Ionescu and Frohman, 2006). The pulses survived, with a higher floor underneath. Nobody has measured whether that floor causes more tolerance than short-acting Mod GRF 1-29, and we found no human data on months of DAC use. Users who prefer the no-DAC form because each dose can be timed have a reasonable point, but no trial has compared the two. Our CJC-1295 profile covers its safety record, including FDA's 2024 review.

Recovery peptides: run length, not cycles

Users usually run BPC-157 and TB-500 for the course of an injury and then stop, instead of cycling on a calendar. Neither acts on the GH receptors above. Rodent and cell studies point to angiogenesis (new blood vessel growth) through VEGF signaling as one BPC-157 mechanism.

Nobody has studied tolerance to either one; the old version of this page said they "don't appear to cause" downregulation, with no data either way. A 2025 systematic review of BPC-157 in sports medicine included 36 studies, and 35 were preclinical; this site rates its evidence as emerging. A typical example is a 2010 rat study in which BPC-157 improved healing of a cut knee ligament (Cerovecki, 2010). TB-500 has less. Anti-doping chemists found that a product sold as TB-500 contained a seven-amino-acid fragment of thymosin beta-4, not the full protein (Esposito, 2012), and the fragment has no human data. Its evidence level here is preliminary.

Users commonly report 250-500 mcg of BPC-157 a day by subcutaneous injection, sometimes split into two doses, and many stop once the injury feels better. The 4-12 week durations in vendor guides haven't been tested. Our guide to stacking peptides within a cycle covers how users combine these with GH peptides.

Goal-timed peptides: AOD-9604 and melanotan II

For these two, users set the run length by the goal: a cutting diet, or the time it takes to reach a tan.

AOD-9604 is a modified fragment of human GH. Users commonly time it to an 8-12 week cut. The earlier version of this page said limited human data suggest it works for fat loss, but FDA's 2024 review of the human trials found otherwise. The largest, OPTIONS, enrolled 536 adults with obesity on oral doses of 0.25-1 mg daily and found no significant difference from placebo in weight loss at 12 weeks, its primary endpoint. Development for obesity stopped, and FDA found no human data for the subcutaneous injections users describe. With no effect shown, run length matters less than whether it works at all. Our AOD-9604 profile has the trial details.

Melanotan II users describe daily or near-daily "loading" doses until they reach the skin tone they want, then a maintenance dose about once or twice a week, or stopping. That pattern comes from user and vendor guides. FDA's compounding safety list cites published case reports of melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome and priapism with melanotan II. Case reports can't prove cause, and a shorter run doesn't make them irrelevant.

Status in sport and medicine

As of October 2026, WADA's 2026 Prohibited List bans CJC-1295, tesamorelin, ipamorelin, hexarelin, GHRP-2, GHRP-6 and ibutamoren under S2.2.4 and AOD-9604 under S2.2.3. TB-500 falls under S2.3 as a thymosin beta-4 derivative, and BPC-157 is named under S0. Melanotan II isn't named; by our reading it falls under S0 as an unapproved substance. An off period doesn't change test status. Of the compounds here, only tesamorelin is currently approved as a prescription medicine in the US (as Egrifta, for excess abdominal fat in HIV-associated lipodystrophy).

What we still don't know

• Whether any cycling schedule gives better results than continuous use. No trial has compared them.
• How quickly sensitivity returns after short breaks, such as two days off. The only human recovery data point is hexarelin after four weeks.
• Whether partial tolerance to GH release changes muscle or fat outcomes. The studies above measured hormones, mostly in older adults, not in people who train.
• How years of on/off use affect blood sugar, given the glucose changes seen with MK-677.
• How much of the fading response users report comes from tolerance, and how much from expectation or inconsistent product quality in gray-market vials.