CJC-1295, ipamorelin and MK-677: the GH and IGF-1 debate

The promise

Growth hormone (GH) secretion declines from mid-puberty throughout life³; in healthy men, age and adiposity were associated with fewer GH bursts and lower daily output¹⁵. In 1990, six months of GH in 12 men over 60 was associated with +8.8% lean body mass and −14.4% adipose tissue, a study that fueled the idea of GH as "anti-aging"¹². Hence the idea of secretagogues, compounds that stimulate the pituitary to release more GH. The most searched are CJC-1295 (a GHRH analog), ipamorelin (a ghrelin-receptor agonist, described in 1998 as the first selective secretagogue)⁸⁹ and MK-677 or ibutamoren, which is taken by mouth and is not a peptide, though it is often sold in the same bundles¹²³.

They do raise GH: CJC-1295

In healthy adults aged 21 to 61, a single dose of CJC-1295 was associated with dose-dependent 2- to 10-fold GH increases for 6 days or more and 1.5- to 3-fold IGF-1 increases for 9–11 days, with a half-life of 5.8–8.1 days and a cumulative effect with repeat doses. No serious adverse reactions were reported in those trials¹. In another study in healthy young men, GH kept coming in pulses after one dose, but trough GH between pulses rose 7.5-fold and IGF-1 rose 45% at one week¹⁰.

Ipamorelin: one trial, negative

Ipamorelin has a single randomized clinical-efficacy trial indexed in PubMed: a phase 2 study with 114 patients analyzed after bowel resection, aimed at speeding recovery from postoperative ileus. Median time to a tolerated solid meal was 25.3 vs 32.6 hours (p = 0.15): there was no significant difference vs placebo in the efficacy analyses, although it was well tolerated². We found no human trials on body composition or aging.

MK-677: the metabolic side

The longest study is of MK-677: a 2-year randomized trial (primary endpoints at one year) in 65 healthy adults aged 60 to 81. It brought GH and IGF-1 to young-adult levels and was associated with +1.1 kg fat-free mass (vs −0.5 kg on placebo) and +2.7 kg body weight (vs +0.8 kg), with no change in strength or function. But fasting glucose rose about 5 mg/dL and insulin sensitivity fell; cortisol rose, and the most frequent side effects were increased appetite (which subsided within a few months), transient mild edema and muscle pain³. In 123 older adults recovering from hip fracture, IGF-1 rose on MK-677 without improvement in most functional tests, and the trial was stopped early for a safety signal of congestive heart failure in a limited number of patients¹¹. With GH itself, a systematic review in healthy older adults found small changes in body composition and more edema, arthralgia, carpal tunnel syndrome and gynecomastia¹³.

The cancer question

IGF-1 stimulates cell growth, and that is the concern. A 2004 meta-analysis associated higher blood IGF-1 with more prostate cancer (OR 1.49 comparing the 75th with the 25th percentile) and premenopausal breast cancer (OR 1.65), with modest associations that varied by cancer type⁴. An analysis of up to 20 prospective studies plus Mendelian randomization found, per standard deviation of IGF-1, an OR of 1.09 for prostate cancer (1.07 with the genetic method)⁵. The other extreme points the same way: in Ecuador, among adults with congenital GH receptor deficiency (very low IGF-1 for life), only 1 of 20 who died did so from cancer, versus 20% of about 1,500 relatives¹⁴.

Two caveats matter. First, these are associations with the body's own IGF-1, not trials of secretagogues. Second, we found no study that has measured long-term cancer risk with these compounds, so the risk is an inference, neither confirmed nor ruled out.