MK-677 vs CJC-1295: What Are The Differences?

In this article, we will examine the differences between MK-677 and CJC-1295, two growth hormone secretagogues. We will understand their mechanisms of action, bioavailability, and potential uses in in clinical and non-clinical settings, such as bodybuilding and equine sports.
Klara Hatinova

Klara Hatinova

Klara is postgraduate researcher in experimental psychology at the
University of Oxford.

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Differences between MK-677 and CJC-1295

MK-677 and CJC-1295 are both growth hormone secretagogues, but they function differently. MK-677, also known as Ibutamoren, stimulates the release of growth hormone through the ghrelin receptor, while CJC-1295, a synthetic GHRH (growth hormone-releasing hormone), increases the body's natural production of growth hormone. The main difference lies in their mechanism of action and their duration of effect, with CJC-1295 having a longer half-life than MK-677.

MK-677 vs CJC-1295

MK-677 and CJC-1295 are supplements that have been studied for their potential effects on growth hormone levels, but they work in different ways and have different properties.

What is MK-677?

MK-677, known as Ibutamoren, is a synthetic, orally active growth hormone secretagogue. It can stimulate human growth hormone (GH) release from the pituitary gland by mimicking the hunger hormone ghrelin [1]. Its ability to be taken orally as a pill contrasts with other growth hormone-stimulating treatments, including CJC-1295, which must be injected [2].

What is the Growth Hormone?

GH is the body's primary anabolic hormone. It is involved in protein synthesis and energy metabolism. Growth hormone production is regulated by growth-hormone releasing hormone (GHRH), somatostatin and ghrelin. These hormones are influenced by stress, exercise and sleep quality and quantity [1].

GH can increase muscle growth and bone density and accelerate injury recovery. It also increases Insulin-like Growth Factor 1 (IGF-1) levels, regulating blood sugar and energy levels.

What is CJC-1295

CJC-1295 is also a growth hormone secretagogue. However, its action is different to MK-677. MK-677 stimulates GH release by mimicking the regulator ghrelin, whereas CJC-1295 mimics the human endogenous growth hormone-releasing peptide, or GHRH. Like MK-677, CJC-1295 also increases IGF-1 levels and changes concentrations of proteins in plasma [3].

The chemical properties of CJC-1295 make it stand out amongst other peptides that increase GH levels. It can covalently bind to plasma proteins such as serum albumin, increasing its half-life—meaning it stays in the body and nervous system longer. This reduces the number of injections one must take. Studies indicate that CJC-1295 can stay in the body for up to 6 days [4].

Bioavailability of MK-677 vs CJC-1295

The timing of the dose will affect the bioavailability of MK-677. The time it takes for MK-677 to reach the nervous system will depend on previous foods eaten, a combination of foods, and the person's metabolism. To maximise absorption, it is recommended that it be taken on an empty stomach in the morning. However, if this causes nausea, your healthcare provider may suggest having some food with your pill.

CJC-1295, on the other hand, is injectable, which means it will have higher bioavailability. As CJC-1295 is a long-lasting GH-releasing hormone stimulant, the interval between doses may vary between 2 and 6 days, depending on the formulation.

MK-677 vs CJC-1295: Uses and Benefits

These uses of MK-677 are promising when applied in the correct clinical settings - for example, to support muscle mass in the elderly, in catabolic conditions, in patients on bed rest or in children with growth hormone deficiency [5]. For example, in a study involving 292 postmenopausal women with low femoral neck bone mineral density, MK-677 increased IGF-1. This was linked to increased bone mineral density and fat-free mass [6]. MK-677 has also been used in diet settings to reverse catabolism - the breakdown of lean body mass - in caloric restriction [7].

CJC-1295, on the other hand, is prominently used in equine sports [8]. This may be because horses tolerate an injectable substance better than humans do. CJC-1295 has also been administered to humans with no significant adverse events [3]. Clinical applications of CJC-1295 are still being explored. An internet chat room search revealed that CJC-1295 is commonly used in bodybuilding, similar to MK-677.


!MK-677 is a banned doping substance in performance sports. Moreover, researchers have found that MK-677 does not improve strength and power, which actually makes it detrimental to many sports performances.

Summary: MK-677 vs CJC-1295

In conclusion, while both MK-677 and CJC-1295 stimulate the production of GH and IGF-1, they do so through different mechanisms and have different properties. More research is needed to fully understand these substances' potential benefits and side effects.

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Klara Hatinova

Klara Hatinova

Klara is a postgraduate researcher in experimental psychology at the University of Oxford. She has worked across a spectrum of hot topics in neuroscience, including her current project measuring reinforcement learning strategies in Parkinson’s disease. Previously, she studied the efficacy of psilocybin as a therapy for critical mental health conditions and examined molecular circadian rhythms of migraine disorders. She completed her undergraduate degree in Neuroscience at the University of Glasgow and participated in a year abroad at the University of California, where she worked on a clinical trial for spinal cord injury.