Sermorelin is an injected GHRH analog that was once FDA-approved and is now compounded by pharmacies on prescription. MK-677 (ibutamoren) is an oral ghrelin mimetic that has never been FDA-approved and that the FDA lists among compounding substances with significant safety risks. Its one-year trial in older adults raised growth hormone and lean mass but also raised fasting blood sugar.
At a glance
| Sermorelin | MK-677 (ibutamoren) | |
|---|---|---|
| What it is | A 29-amino-acid peptide, the active fragment of growth hormone-releasing hormone | A small non-peptide molecule that mimics ghrelin |
| Receptor | GHRH receptor on the pituitary | Ghrelin receptor (GHS-R1a) |
| How it is taken | Nightly injection under the skin; compounded tablets also sold | Once-daily pill or liquid; 25 mg in the main trials |
| FDA status | Approved as Geref from 1990; discontinued, not for safety reasons [4] | Never approved; in FDA compounding Category 2 for significant safety risks [5] |
| Longest adult trial | 5 months, 19 adults aged 55 to 71 [1] | 2 years, 65 adults aged 60 to 81 [2] |
| Blood sugar in trials | Fasting glucose and insulin unchanged [1] | Fasting glucose up 0.3 mmol/L; insulin sensitivity down [2] |
How do sermorelin and MK-677 work differently?
Both end in the same place, more growth hormone from your own pituitary, but they get there through different doors. Sermorelin copies the first 29 amino acids of growth hormone-releasing hormone, the signal the hypothalamus sends each night. It binds the GHRH receptor and produces a pulse within about ten minutes that lasts around two hours [1]. Because it is a peptide, the stomach would digest it, which is why the studied form is an injection.
MK-677 is not a peptide at all. It is a small synthetic molecule that activates the ghrelin receptor, the one that responds to the stomach’s hunger hormone. That receptor also triggers growth hormone release, and because the molecule survives digestion it works as a pill. In older adults, 25 mg a day nearly doubled average 24-hour growth hormone, up 97% after two weeks, by making the body’s existing pulses larger [3]. Ipamorelin uses the same receptor as MK-677, so sermorelin vs. ipamorelin covers much of the same mechanism from the injectable side, and the guide to growth hormone peptides sets out both receptor classes.
Which has better human evidence?
On size and length, MK-677 does. Its main trial in healthy older adults ran two years, enrolled 65 people and was double-blind. After one year, fat-free mass rose 1.1 kg on MK-677 and fell 0.5 kg on placebo (P < 0.001). But abdominal visceral fat did not change, body weight rose 2.7 kg against 0.8 kg, and the extra lean mass “did not result in changes in strength or function” [2].
The larger patient trials were less encouraging. In 563 people with mild to moderate Alzheimer’s disease, a year of MK-677 raised IGF-1 by 72.9% and did nothing measurable for the disease [6]. In 123 older adults recovering from hip fracture, it raised IGF-1 but did not improve most measures of function. That trial was stopped early for a safety signal of congestive heart failure [7].
Sermorelin’s adult record is smaller: one placebo-controlled trial of 19 people over five months. Lean body mass rose in the nine men but not the ten women, and skin thickness rose in both [1]. The trial is covered in full in does sermorelin work. So MK-677 has the bigger evidence base. Much of what that evidence shows is that raising IGF-1 is easy and turning it into a benefit people can feel is not.
Is MK-677 legal to prescribe?
Not as an approved drug, and the FDA has flagged it for compounders too. The FDA’s drug approvals database has no record of ibutamoren under any name [8]. On the FDA page that lists bulk substances for compounding that may present significant safety risks, “Ibutamoren mesylate” appears in Category 2 for both traditional pharmacies (503A) and outsourcing facilities (503B), as of the FDA page updated April 22, 2026. The stated reason: it “poses significant safety risks due to the potential for congestive heart failure in certain patients” [5]. In practice that leaves MK-677 sold mainly as a “research chemical” or a supplement, the channel prescribed vs. research sermorelin explains.
Sermorelin is in a different position. It does not appear on that Category 2 page, and its approved brand was discontinued with an FDA determination that the product “was not discontinued or withdrawn for safety or effectiveness reasons” [4]. That history is part of why pharmacies can still compound it on a prescription, and why sermorelin’s FDA status reads differently. One footnote on the pill side: the only ghrelin receptor agonist the FDA ever approved was macimorelin (Macrilen), an oral solution for diagnosing growth hormone deficiency in adults, not for treatment. It is also now discontinued [9].
For athletes, the comparison ends early. The World Anti-Doping Agency names both drugs on its 2026 Prohibited List under section S2.2.4: sermorelin among GHRH analogs, and ibutamoren (MK-677) among growth hormone secretagogues. Both are prohibited at all times [10].
What are the side effects of each?
MK-677’s most frequent side effects in the two-year trial were increased appetite that faded over a few months, mild temporary leg swelling and muscle pain. Fasting glucose rose an average of 0.3 mmol/L (5 mg/dL), insulin sensitivity fell, and cortisol rose [2]. In an earlier four-week study at the same dose, fasting glucose climbed from 5.4 to 6.8 mmol/L [3]. The appetite effect is no surprise, since ghrelin is the hunger hormone; the glucose effect is the one a prescriber would watch.
Sermorelin’s adult trial reported only a temporary rise in blood lipids, with fasting glucose and insulin unchanged and insulin sensitivity improving in men [1]. That trial was far smaller and shorter, so the clean result says less. The full sermorelin picture, including pediatric data, is in sermorelin side effects.
Why does the pill vs. injection difference matter?
For most buyers the attraction of MK-677 is the pill. That convenience comes from its chemistry: a small molecule survives the gut and a peptide does not. It is also why oral sermorelin is a harder product to judge. Compounded sermorelin tablets and troches exist, but the published trials used injections, and the question of how much survives by mouth is examined in sermorelin tablets. The two drugs also shape growth hormone differently in time. A nightly sermorelin injection produces one pulse of a couple of hours, while a daily MK-677 dose raised 24-hour levels, including the troughs between pulses [3].
Can you take sermorelin and MK-677 together?
The pairing is sold, usually on the idea that hitting two receptors gives a bigger growth hormone release than either alone. No study has tested sermorelin with MK-677 itself. A PubMed search for the two together returns one record, a 2020 review rather than a trial [12]. The closest human data used GHRP-2, which acts on the same ghrelin receptor as MK-677. In eight healthy men aged 25 to 34, a single intravenous dose of the two together produced a larger growth hormone response than either alone, but no more than the sum of the two separate responses. The authors “were not able to demonstrate synergy” [11].
That was one injection in a lab, not months of daily use, so it neither proves nor rules out a benefit from stacking. It does mean the “synergy” claim rests on mechanism rather than measured results. Combining them also stacks the side effects that matter most, MK-677’s effect on blood sugar among them. The broader question of combining peptides is covered in sermorelin stacks.
Bottom line
MK-677 has longer and larger trials than sermorelin, and those trials show it raises growth hormone, IGF-1 and lean mass in older adults. They also show higher blood sugar, an appetite surge, no gain in strength or function, and a heart-failure signal that ended one study and put it on the FDA’s list of compounding safety risks. Sermorelin’s evidence is thinner, but it is the one of the two that can be prescribed and filled by a licensed pharmacy today. To see how sermorelin fits with the other growth hormone peptides, compare sermorelin, tesamorelin and ipamorelin, or start with how to get a sermorelin prescription.