If you’ve been reading about SARMs and research chemicals, you might already know that some have the potential to cause sexual side effects due to endogenous testosterone suppression.
MK-677 is not a selective-androgen-receptor-modulator and does not suppress testosterone. Nevertheless, you might have run into users claiming it caused erectile issues. On paper, MK-677 can cause erectile issues because it increases prolactin. But in reality, erectile issues from it are extremely unlikely and rare.
In this article I’ll explore the topic of ED from MK-677 based on the clinical data we have as of January 2025, my own personal experiments with myself and dozens of clients, and the experiences of thousands of users who have used MK-677 and posted online.
MK-677 will increase your prolactin levels. Prolactin is the hormone responsible for milk production in females, and in men, high levels of prolactin can cause gynecomastia, low sex drive, and even erectile dysfunction.
So how much of a risk factor is taking MK-677?
In a clinical study on MK-677 by the Journal of Bone and Mineral Research, healthy and functional elderly adults were given 25 mg/day of MK 677 for 2-9 weeks. By the 9th week, their serum prolactin had increased by 27%. Right after the discontinuation of treatment with MK-677 it returned to baseline.
While a 27% increase sounds like a lot, it is not high enough to cause erectile dysfunction or erectile issues by itself. Especially in young and healthy men. Not to mention that most users do not take 25 mg/day but are closer to 10 mg/day.
Even though extremely rare, erectile dysfunction with MK-677 is still possible in men who have a pre-existing disbalance between their testosterone and estrogen levels, high prolactin levels, and a history of erectile issues. This means that men who are already prone to erectile issues run the risk of exacerbating them by taking MK-677 if the root is hormonal.
If you fall into this group and are concerned, you can be 100% on the safe side of things by getting bloodwork done and testing your prolactin and testosterone levels. If your baseline is within the reference range, you will not experience any prolactin-related side effects.
Preventing issues before they arise is much easier than dealing with them afterward. And fortunately, preventing erectile dysfunction while on MK 677 is very simple.
It comes down to reversing the increase in prolactin, which can be easily done by supplementing with:
Even though the risk of ED from MK-677 is incredibly small, do this even if you aren’t prone to ED as this amount of P5P will have a good impact on your sleep quality without any negative side effects.
If you fall into the group at risk, start with a small dose of MK 677 and slowly increase it whilst actively monitoring for prolactin-related side effects.
I believe that the majority of erectile dysfunction reports from MK 677 are because of a fake product.
Unfortunately, while it’s not as common as it was a few years ago, many companies still sell fake MK-677 cutting corners whenever possible despite it being one of the cheapest research chemicals to manufacture.
Erectile dysfunction from MK 677 is extremely rare and can only happen to people with very high baseline prolactin levels, low testosterone levels, and if the MK 677 is fake.
If you’re concerned and want to be 100% safe, you can go the extra mile to get your prolactin levels tested.
But supplementing with P5P during your MK 677 cycle will prevent ANY potential prolactin-related side effects, including erectile dysfunction.
premium resources
Everything you would ever want or need to know about SARMs to use and recover from them. Also includes other research chemicals.
An all-in-one guide that will teach you how each of the peptides works, how you can use them and find the perfect one (or stack) to reach your goals.
Wish there was ONE comprehensive, easy-to-read guide to get you fully informed on the safe and effective use of anabolic steroids?
Improve penile function, get harder fuller and longer-lasting erections, increase stamina in bed and last longer, go more rounds. All the good stuff.
A summary of everything you NEED to know about using PHs as safely as possible, supplements to stay as healthy as possible during cycles and how to recover (PCT).
A document I originally made for my clients. A neat map to the sphere of PEDs and supplements.
You'll receive the link and a once-a-week PED-related article in your inbox upon subscribing.
A special gift to all my email subscribers. The PED Dictionary is a DOC designed to help you navigate the world of enhanced bodybuilding. A game changer for beginners that want to learn more but don't know where to start, and a must-have handbook for even the most advanced enhanced researchers.
