MK-677 is known as a selective androgen receptor modulator (SARM), however it technically does not fit into this category.
This drug is actually a growth hormone secretagogue that acts as an agonist to secretagogue-receptors. By doing so it is thought to increase growth hormone secretion in the body .
Growth hormone secretion by the pituitary gland is controlled mainly by two hypothalamic peptides: somatostatin (inhibitory) and growth hormone-releasing hormone (stimulatory).
Growth hormone is thought to be closely linked to aging as it directly stimulates IGF-I production and may influence muscle development, strength, fat loss, and bone mineral density.
In most scenarios, aging is associated with decline in serum concentrations of growth hormone and IGF-I .
By the time a person reaches 70 years old, they have lost ~5kg of muscle mass while also increasing their intra-abdominal fat stores .
Deficiencies in growth hormone can predispose people to premature diseases such as sarcopenia, osteoporosis, and even cardiovascular diseases.
It is well-known that such issues can be partially reversed by the administration of growth hormone drugs , however standard growth hormone therapy has many negatives such as:
- High cost
- Parenteral administration
- Fluid retention
- Carpal tunnel syndrome
- Glucose intolerance
Does MK-677 Work?
May Increase Growth Hormone Levels
MK-677 is a spiropiperidine that mimics the actions of other growth hormone drugs by binding to non-somatostatin receptors in the pituitary and stimulating growth hormone secretion via protein kinase C- and calcium-dependent mechanisms .
When MK-677 is given to elderly individuals, there is a notable sustained increase in the levels of growth hormone secretion and IGF-I levels to similar levels as observed in young adults.
Specifically, 25mg per day in elderly adults increases growth concentrations by ~90% after just 1 month .
After 6 months of MK-677 administration, increases in lean body mass of ~2kg have been observed – partly due to greater intracellular water .
This benefit has made MK-677 one of many potential future anti-aging drugs  that may partially reverse the effects of aging by increasing the height of the growth hormone pulses and the concentrations of growth hormone between pulses .
May Increase Appetite
As MK-677 also elevates ghrelin levels (“hunger” hormone) in the body, it is also known to transiently stimulate appetite, which has been proposed as a novel effect that might counteract physiological anorexia .
The combination of increased growth hormone and appetite is obviously an attractive combination for those trying to gain weight, and in clinical situations to stop muscle wasting. This is why MK-677 is a potential drug to prevent sarcopenia, a disease that is the hallmark of frailty and is associated with increased mortality in the elderly .
Studies in older adults have shown positive results, with 2 years of MK-677 use counteracting the development of sarcopenia, loss of fat-free mass, and inadequate food intake .
MK-677 Safety And Side Effects
The safety of MK-677 has not yet been determined. Research on the compound is very limited, and there are currently very contradicting results for health.
On one hand MK-677 has also been able to reduce LDL (“bad”) cholesterol levels after 1 year of administration, but on the other it has increased insulin resistance and blood glucose levels in the elderly .
The main potential issue with MK-677 appears to be its negative impact on carbohydrate metabolism, that could seriously end up limiting the usefulness of the drug.
So far, the most frequent side effects are:
- Mild edema
- Muscle pain
- Increased appetite
However, at least it is seemingly a safer option to the standard use of growth hormone therapy in clinical settings, which has been linked to:
- Serious edema
- Carpal tunnel syndrome
- Impaired fasting glucose
MK-677 is a growth hormone secretagogue that has been falsely categorized as a SARM.
It is a potential future alternative to standard growth hormone therapy, with good evidence that it can increase growth hormone and IGF-1 levels in adults.
However, it may negatively affect carbohydrate metabolism and far more research is needed before it can be recommended for human use.