What is MK-677?
MK-677 is the popular name for the synthetic steroid Ibutamoren. MK-677 is a growth hormone secretagogue, which means it enhances Growth Hormone (GH) and Insulin-like Growth Factor 1 (IGF-1) release by mimicking the effects of the peptide for weight loss, ghrelin.
Ghrelin is the primary hunger hormone released from the stomach, commonly associated with the stomach growling when you are hungry. However, ghrelin can also stimulate the release of growth hormone (GH) and, consequently, Insulin-like Growth Factor I (IGF-I) [1, 2, 3]. This property of ghrelin makes MK-677 a popular supplement to enhance GH and IGF-1 levels in people with growth hormone deficiencies or recreationally muscle-building athletes. However, MK-677 is not an approved supplement and is banned by the anti-doping agency [4].
MK-677 Stimulates Growth Hormone
Growth Hormone is the critical downstream hormone that facilitates many benefits attributed to MK-677. These include tendon growth in adolescence, tissue healing, Injury recovery, muscle growth, and cell specialisation [5]. Similarly, IGF-1 is critical for anabolic growth, which can promote cell growth and division and inhibit cell death [5].
In the following sections, we will cover the scientific evidence about MK-677 and testosterone, focusing mainly on the link between GH, the downstream hormone MK-677, and testosterone.
MK-677 Side Effects
As with other supplements, taking MK-677 comes with side effects. In our previous blogs, we discussed the link between MK-677 and cancer, brain damage, or how MK-677 may influence erectile function.
MK-677 and Testosterone
MK-677 stimulates the release of growth hormone (GH) and insulin-like growth factor-I (IGF-I) in the body. It has been studied for its potential effects on body composition, muscle mass, and hormone levels, which are also associated with testosterone.
Several studies have looked at the link between MK-677 and testosterone:
One study found that MK-677 treatment in obese males decreased serum total testosterone levels. However, the ratio of total testosterone to sex hormone-binding globulin (SHBG), an index of free testosterone, remained unchanged. This suggests that while MK-677 may reduce total testosterone levels, it does not appear to affect the levels of bioavailable testosterone in the body [6]. These results have implications for using MK-677 in bodybuilding and as a supplement therapy for growth hormone deficiencies.
In another case study, a 25-year-old male who combined MK-677 with LGD-4033 for five weeks experienced a significant decrease in both free and total testosterone levels. However, these levels returned to pre-cycle values after the treatment period, suggesting that the impact on testosterone levels may be temporary [7]. This study demonstrates the critical importance of drug and supplement combinations. It underscores the necessity to report all drugs and supplements to your healthcare provider so they can account for any interactions.
To summarise, MK-677 reduces total testosterone levels, although this may not alter the amount of bioavailable testosterone. Hence, you may not register any physical changes relating to testosterone. Critically, the studies presented are limited to drawing firm conclusions, especially when taken in bodybuilding settings, growth hormone therapy or when combined with other drugs.
MK-677 And Testosterone: A Connection Between Testosterone And Growth Hormone?
What is the interaction between growth hormone and testosterone?
Growth hormone (GH) and testosterone interact synergistically to influence body composition and protein metabolism. Testosterone alone can decrease protein oxidation rates by 28%, and this effect is enhanced to a 36% decrease when combined with GH [13]. Testosterone and GH together can increase fat-free mass [14]. Testosterone also shows a positive correlation with insulin-like growth factor-binding protein-1 (IGFBP-1), which actively regulates the cellular actions of IGF-I, a mediator of GH effects [15]. However, the exact mechanisms of these interactions are complex and not fully understood.
Several studies have shown that testosterone supplementation can increase GH and IGF-I levels in men. This is the opposite of what supplementing MK-677, a growth hormone secretagogue, was demonstrated to do.
In a study involving healthy older men at risk of age-related testosterone reductions, testosterone supplementation increased GH and IGF-I concentrations [8]. This shows the beneficial effect of testosterone on maintaining muscle and bone mass.
Another study involving healthy men found that when a testosterone formulation was administered, serum IGF-I levels increased after six weeks of treatment [9, 10].
In a study involving hypogonadal men, meaning men with reduced function of the sex organs, testosterone treatment significantly increased circulating IGF-I levels [11, 12]. This finding is particularly relevant for congenital diseases linked to insufficient testosterone production. Insufficient testosterone can affect not only sexual development but also growth, bone mineral density, bone health, lean muscle and skin elasticity. In this instance, there is evidence to support using testosterone for growth enhancement instead of growth hormone replacement therapy, for example, by MK-677.
Furthermore, both MK-677 and testosterone have anabolic functions and a common target of increasing growth hormone. Hence, MK-677 has similar functions, although it may not have a clear role in increasing/decreasing testosterone levels.
Summary: MK-677 and Testosterone
To summarise, there is preliminary evidence that taking MK-677, a growth hormone secretagogue, could reduce testosterone levels in men. However, both MK-677 and testosterone have anabolic functions, which means they may counteract each other rather than complement each other.
Finally, MK-677 is a banned doping substance with potential side effects, so exercise extreme caution when considering supplementing with MK-677.