Are you trading erections for looking bigger and more ripped?

Have you gotten erectile dysfunction from MK-677?

In this article, I’m going to show you why MK-677 might cause ED, and how it can actually help with erections as well.

What is MK-677 (Ibutamoren mesylate)

Ibutamoren is an oral medication, non-peptide agonist of the ghrelin receptor. Activation of the ghrelin receptor promotes the release of growth hormone levels (GH) from the pituitary gland. Thus MK-677 mimics the growth hormone-stimulating action of ghrelin.

MK-677 was designed to boost growth hormone production in people with a medical condition of growth hormone deficiency. This deficiency limits growth during youth.

Additionally, many elderly adults tend to have low growth hormone, thus boosting GH can help retain muscle, get rid of body fat and improve sleep quality.

Other common GH secretagogues include pralmorelin (GHRP-2), GHRP-6, examorelin (hexarelin) & ipamorelin.

Since MK-677 is a ghrelin receptor agonist, it will likely have many similar actions to ghrelin itself.

Ghrelin receptors are widely expressed in:

• Many brain regions
• Pituitary
• Intestine
• Kidney
• Thyroid gland
• Lung
• Heart
• Pancreatic islets
• Ovaries
• Testis
• Sebaceous glands

Thus, MK-677 can have effects on all those tissues.

Let’s look at what effects ghrelin has.

Ghrelin is important for:

• Learning
• Memory
• Cognitive function
• Reward
• Sleep
• Taste sensation
• Smell, and sniffing

Ghrelin has the following effects:

• sympatholytic (stimulates the sympathetic nervous system)
• analgesic (blunts pain)
• antimicrobial
• antifibrotic
• osteogenic (improves bone mineral density)

Ghrelin:

• Makes the skeletal muscle more excitable
• Stimulates muscle regeneration following injury and promotes wound healing
• Delays puberty
• Promotes fetal lung development
• Decreases thyroid hormone and testosterone levels
• Stimulates the release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin
• Inhibits insulin release
• Protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. 

Quite a comprehensive list.

Ghrelin is released mostly during fasting. So using MK-677 can artificially signal a state of fasting.

Thus, providing a fasting signal and then eating at the same time, could have some undesirable effects. More on that later.

Can MK-677 cause erectile dysfunction?

There are no clinical studies showing that MK-677 can cause erectile dysfunction, nor was this side effect ever mentioned in the trials looking at MK-677.

However, let’s look at a few of the possible mechanisms for how someone might get ED when taking MK-677.

MK-677 increases prolactin

This is by far the most common theory of why MK-677 might cause ED.

Prolactin has been shown to inhibit penile erection, particularly at the penile base. This becomes more obvious when the erection time lasts longer than 10 min (R).

Prolactin can inhibit erections by (R):

• Lowering testosterone production.
• Inhibiting dopamine release.
• Inhibiting 5-alpha reductase and DHT production, which can also contribute to ED.
• Inhibition of smooth muscle relaxation of the penile corpus cavernosum.

However, the increase in prolactin-induced by MK-677 seems to be small. Here are 2 studies showing a slight increase.

#1 After 8 weeks on 25mg MK-677, prolactin increased by 23%, from 7 to 8.6ug/L (R). Not a big jump and unlikely to contribute to ED.

#2 25mg MK-677 increased prolactin to 34.6ng/mL right after starting, which then dropped to 16.8 and 17.5ng/mL at weeks 2 and 8 respectively (R). Prolactin levels in the placebo group were 10.5 at the start, which then increased to 13.6 and 13.3ng/ml after 2 and 8 weeks respectively. It’s likely that these men had slightly elevated prolactin even before starting MK-677.

However, these three studies found no increase in prolactin on MK-677 (R, R, R).

In summary, is the MK-677-induced prolactin causing ED? Unlikely, unless someone already has high prolactin or is unhealthy to the point that a small increase in prolactin will send them over the top.

The most common recommendation for MK-677-induced ED is 100mg of vitamin B6. B6 helps lower prolactin by promoting dopamine production. It’s likely that people who benefit from B6 supplementation are low, to begin with.

Instead, optimize your diet as well, while using MK-677. Then you’ll have no need for supps.

MK-677 lowers testosterone

The only study looking at the effects of MK-677 on testosterone found that it slightly lowered testosterone.

25mg MK-677 decreased testosterone from 22.4 (646ng/dl) to 19.7 to 20.7 (597ng/dl) after 2 and 8 weeks respectively. That’s a small 49ng/dl decline. Their testosterone was just under 600, which is more than enough for proper erections (R).

There aren’t any studies looking at MK-677 and aromatase and estradiol production, but ghrelin has been shown to lower aromatase (R). This would mean that activation of the ghrelin receptor (by MK-677 for example) is likely to lower estradiol.

The reason I bring this up is because a high estradiol-to-testosterone ratio contributes to ED. If MK-677 increased estradiol, it might have contributed to ED via this mechanism, but it seems unlikely.

MK-677 stimulates the sympathetic nervous system

The sympathetic nervous system helps with arousal and getting an erection. However, too much stimulation will kill libido and contribute to premature ejaculation.

Sympathetic stimulation is responsible for vascular smooth muscle contraction of the penis as well as the promotion of the release of noradrenaline, adrenaline and cortisol. In high amounts that are unfavorable.

Contraction of the smooth muscle tissue of the penis inhibits the ability to get erections.

Ghrelin increases muscle sympathetic nervous system (R). So it’s possible that MK-677, by activating the ghrelin receptor, might be able to do the same.

Interestingly, MK-677 has been shown to lower blood pressure.

MK-677 might worsen insulin sensitivity

Studies show that MK-677 can increase fasting glucose and insulin. This is a sign of insulin resistance. This is what should happen when you fast. However, on MK-677, people aren’t fasting. So you’re sending fasting signals while eating, which then creates insulin resistance and impaired glucose handling.

The prevalence of ED is approximately 3.5‐fold higher in men with diabetes than in those without diabetes (R).

If you already have high fasting glucose and then go on MK-677, it might likely make it worse. High blood sugar can contribute to vascular inflammation, which can worsen erectile function over time.

A lot of people use MK-677 to lose fat and insulin resistance is commonly found in overweight individuals.

Plus, if you’re already insulin resistant, and then eat a ton of food because you’re super hungry on MK-677, that will worsen glucose handling even more.

MK-677 might cause performance anxiety-induced ED

There is evidence showing that MK-677 can worsen anxiety in predisposed individuals. Many users report the same thing. If MK-677 makes you nervous, this might be a boner killer.

How MK-677 can help with erections

More likely than not, MK-677 will boost your libido instead of lower it. High libido is more likely to help with erections.

Here are a few ways how MK-677 can help with erections.

MK-677 boosts growth hormone

Growth hormone spikes when you get an erection.

Men with organic ED (of vascular origin) have lower baseline growth hormone and a blunted rise in growth hormone during erections (R). In the first graph, you can see how GH spikes as you get an erection. In the graph on the right, you can see that GH is much lower in men with ED and that they have a blunted spike in GH.

By boosting GH, MK-677 is likely to help with erections.

MK-677 might also be able to keep your GH normal for a long time.

25mg MK-677 increase GH to normal levels and kept it there for at least 12 months. GH levels increased by 1.8 fold and IGF-1 levels also increased by 1.5 fold in the treatment groups (R).

MK-677 boosts insulin-like growth factor-1 (IGF-1)

25 mg/day MK-677 increased mean serum IGF-I concentrations from 141microg/L at baseline to 219 and 265microg/L at week 2 and 4 (R).

High GH will lead to higher IGF-1.

IGF-1 is positively correlated with sexual function (R) and promotes DHT and nitric oxide (NO) production.

If you’re not getting a decent boost in sexual function from MK-677, it might be that your GH and IGF-1 aren’t spiking high enough.

MK-677 might increase dopamine

Ghrelin agonists promote motivation by boosting dopamine in mice (R). Dopamine helps to promote sexual desire and sexual function (R).

On the flip side, ghrelin decreases sexual behavior in rats (R).

Since we are neither mice or rats, it’s hard to say what will happen to your libido on MK-677. According to online anecdotal evidence, some people do report a boost in libido, whereas others don’t.

As an aside, ghrelin increases during fasting. During fasting, testosterone and T3 drop to slow the basal metabolic rate. Sexual function also goes down. Ghrelin agonists might do the same.

Other benefits of MK-677

Muscle sparing effect

MK-677 has a strong muscle-sparing effect during a deficit and can even boost lean body mass and muscle growth.

During a caloric deficit without MK-677, nitrogen loss was 2.67g/day. On MK-677, the nitrogen balance was 0.31g/day (R). It went from a minus to a positive. Building muscle in a deficit.

Due to its muscle-sparing effect, it can also be very helpful against muscle wasting.

No PCT required

No side effects when stopping. Once you stop, GH and IGF-1 will likely go back to where they were before you started. Since MK-677 doesn’t suppress natural testosterone production, you don’t have to PCT or anything. It’s also not a selective androgen receptor modulator (SARM), so it does mess with your androgenic system at all.

Might improve thyroid hormone levels

This study found that 25mg MK-677 increased free T3 from 5.66 to 6.04pmol/L after 8 weeks (R).

Unlike ghrelin which suppresses thyroid function, MK-677 doesn’t seem to do the same.

Might help with hair regrowth

IGF-1 promotes hair growth, so restoring IGF-1 to normal might help (R).

Improves sleep quality

In young subjects, 25mg MK-677 increased deep sleep (stage 4) by 50% and REM (rapid eye movement) sleep by 20%. It also corrected a lot of deviations from normal sleep.

In older adults, treatment with MK-677 increased REM sleep by 50% and decreased the frequency of deviations from normal sleep (R).

Most people using MK-677 report improvements in sleep quality.

Adverse side effects of MK-677

Might worsen insulin resistance and glucose handling

Increases fasting blood sugar levels and contributes to insulin resistance. 25mg increased fasting glucose from 5.4 to 6.8nmol/L after 4 weeks (R).

Since ghrelin increases during fasting to promote lipolysis and gluconeogenesis (production of glucose), you can expect to become a little more insulin resistant. It’s supposed to happen when you fast.

Heart problems

This trial was terminated early due to a safety signal of congestive heart failure in a limited number of patients (R).

Massively increases appetite

Since ghrelin is the hunger hormone, activating its receptor with MK-677 does the same.

It might be helpful for someone with low appetite, but most people can do with less appetite.

This review cracked me up:

“I forgot about the hunger thing when i went fishing the otherday and took a decent dose before i left… BROOOO… IN the middle of fishing i told the people i was with im hungry and they offered me their cookies and i said it wasnt enough.. Man i fuckin left Speeding to the store @90mph almost in tears because i was SO FUCKIN HUNGRY I ate like 3hunnybuns+ 2cupcakes+ fuckin m&ms and a big ass bag of chips 😂😂😂. That shit was brutal as fuck. 😂😂😂.” (R)

Might make you more anxious

Ghrelin receptor agonists enhance fear memory (R). It might mean that MK-677 might make someone more anxious/fearful.

Quite a few people report that MK-677 significantly worsened their pre-existing anxiety (R). If you don’t have anxiety, MK-677 will likely not cause it.

But if you have anxiety, or are pre-disposed to it, it might definitely worsen your anxiety.

Neutral effects of MK-677

MK-677:

• Doesn’t affect cortisol levels (R).
• Likely doesn’t affect the metabolic rate long-term (R).

Does MK-677 cause ED? Summary

It’s possible that MK-677 might contribute to ED by 1) increasing prolactin 2) lowering testosterone 3) worsening insulin resistance and 4) causing anxiety. However, these effects are likely too small to cause any real issues, unless they were already suboptimal before starting MK-677.

However, MK-677 is more likely to improve erections by 1) improving libido, 2) increasing GH, 3) increasing IGF-1 and 4) increasing dopamine.

Is MK-677 worth it?

MK-677 can speed up fat loss and help retain muscle mass during a deficit. We all want fast results. But if it lowers your quality of life, it’s not worth it.

Stick to good dietary and lifestyle habits that will ensure that you lose fat and build muscle over the long run. Hopefully, you’re in this for the long run which will be a couple of decades. If that’s the case, diet, exercise, sleep, sunlight, etc., will be the best bang for your buck.