MK-677 is one of the few compounds in this space that’s been tested in people for years, not weeks.
The longest trial ran for two years. So when it comes to side effects, there’s real data on what showed up, how often, and which ones faded on their own.
Here’s what the human trials found, the one side effect you need numbers to catch, and a blood sugar tracker you can use while you’re on it.
MK-677 at a Glance
| MK-677 (Ibutamoren) | |
|---|---|
| What it is | An oral compound that copies ghrelin to trigger growth hormone release, developed by Merck |
| How it’s taken | By mouth, once a day |
| Dose used in most human trials | 25 mg daily |
| What it raises | Growth hormone (GH) and IGF-1 |
| Longest human trial | 2 years |
| Most common side effects | More appetite, water retention, muscle and joint aches, tingling hands |
| The one to watch | Blood sugar and insulin sensitivity |
What Is MK-677?
MK-677, also called ibutamoren, was developed by Merck in the 1990s. It’s a small molecule rather than a peptide, which is why it survives your stomach and works as a pill. It does the same job as growth hormone peptides like ipamorelin, though, so it lives in the same conversation.
It works by copying ghrelin, your hunger hormone. Ghrelin has a second job: it tells your pituitary gland to release growth hormone. MK-677 binds the same receptor and switches on both jobs.
The effect is strong. In a study of healthy adults aged 64 to 81, 25 mg a day nearly doubled their 24-hour growth hormone output (up 97%) within two weeks. IGF-1 climbed from 141 to 265 µg/L in four weeks, which is normal for a young adult.
That’s why people take it: more lean mass and deeper sleep, from one pill a day.
Where MK-677 Side Effects Come From
Almost every MK-677 side effect traces back to one of those two jobs:
- The ghrelin side: hunger.
- The growth hormone side: fluid retention, aches, tingling hands and higher blood sugar.
Growth hormone works against insulin. Raise it every day and blood sugar tends to drift up, which is why that’s the side effect this whole article keeps coming back to.
MK-677 Side Effects: What the Human Trials Found
The best data comes from a trial published in the Annals of Internal Medicine in 2008. Sixty-five healthy adults aged 60 to 81 took 25 mg of MK-677 or a placebo every day. The trial ran for two years, with the main results measured at one year.
Here’s what changed in that first year:
The shorter trials fill in the rest of the picture. Here’s every side effect they turned up, starting with the one almost everyone notices.
Increased Appetite
MK-677 copies the hunger hormone, so this one is no surprise. Expect to be hungrier, especially in the first weeks.
In the 2-year trial, the extra appetite settled back down within a few months.
It’s also part of why the scale moves. Over the first year, the MK-677 group gained 2.7 kg, against 0.8 kg on placebo. About 1.1 kg of that was lean mass, while the placebo group lost 0.5 kg. Fat on the arms and legs went up too: 1.1 kg, against 0.24 kg on placebo.
Water Retention and Swelling
Mild swelling in the lower legs showed up in the 2-year trial, and it passed.
A shorter trial in obese men shows how much of the early weight is water. After 8 weeks on 25 mg, they were 2.7 kg heavier. One week after stopping, they were only 1.8 kg heavier. A third of the gain was gone in seven days, and that fast drop is fluid leaving.
Fluid retention is the classic growth hormone side effect. The Endocrine Society’s guideline on GH treatment puts fluid-related side effects at 5 to 18% of treated adults. Most are dose-related and improve when the dose comes down. Older, heavier and female adults are more prone to them.
Muscle and Joint Aches
Muscle pain was one of the side effects reported in the 2-year trial. Achy, stiff joints are on the same fluid-retention list in the Endocrine Society guideline.
Tingling or Numb Hands
Fluid around the wrist can squeeze the nerve that runs into your hand. That’s carpal tunnel syndrome, and it shows up in about 2% of adults on growth hormone treatment.
Tingling or numb fingers, often worse at night or first thing in the morning, is one of the most common complaints from MK-677 users. Like the swelling, it usually eases when the dose comes down.
Higher Blood Sugar and Lower Insulin Sensitivity
This is the one that matters most, because you can’t feel it. Three trials, three angles on it:
- 2-year trial in older adults: fasting blood sugar rose 5 mg/dL on average, and insulin sensitivity went down.
- 4-week study in older adults: average fasting blood sugar went from 5.4 to 6.8 mmol/L, about 97 to 122 mg/dL. That’s a move from normal into the prediabetes range.
- 8-week trial in obese men: fasting blood sugar and insulin stayed flat, but the glucose tolerance test, which checks how you handle a sugar drink, got worse at 2 weeks and again at 8 weeks.
That last one is the lesson. Fasting blood sugar can look fine while your body handles meals worse, so tracking more than one marker catches more. I’ll show you how below.
Cortisol and Prolactin
Some growth hormone boosters that work through the ghrelin receptor push up cortisol (your stress hormone) and prolactin. With MK-677, both moved only a little.
Cortisol rose 1.7 µg/dL on average over a year in the 2-year trial, and stayed flat in the 4-week and 8-week studies. Prolactin went up 23% in the 4-week study and stayed in the normal range.
Changes in Sleep
MK-677 changes how you sleep. In a sleep-lab study, 25 mg increased deep sleep by about 50% and REM sleep by more than 20% in young adults. In older adults, REM went up about 50% and started sooner after falling asleep.
REM is the dreaming stage, so more of it fits the vivid dreams a lot of users mention. Some users also report feeling sluggish in the first few weeks, especially at higher doses.
Who Should Be Most Careful With MK-677
People With High Blood Sugar
If you already have prediabetes, diabetes or a high A1C, MK-677 pushes on the exact system that’s under strain.
People With Heart Failure or Fluid Problems
A 2011 trial gave 25 mg a day for 24 weeks to 123 older adults recovering from a hip fracture. IGF-1 rose and walking speed improved slightly, but the trial was stopped early after a small number of patients developed congestive heart failure. The researchers concluded MK-677 had an unfavorable safety profile in that group.
Heart failure is a condition where extra fluid is already the problem, and fluid retention is the most common thing MK-677 does.
People With a History of Cancer
MK-677’s whole job is raising IGF-1, a hormone that tells cells to grow. If you’ve had cancer, that’s a conversation to have with your doctor first. I go deeper on this in MK-677 and cancer: is there a link?
People With Carpal Tunnel or Joint Problems
If your wrists or joints already give you trouble, the fluid side of MK-677 tends to find them first.
How to Track Your Blood Sugar on MK-677
Blood sugar is the side effect you can’t feel, so it’s the one to put numbers on. Two tests cover it:
- Fasting glucose: a finger-prick reading first thing in the morning, at least 8 hours after you last ate. A home glucose meter does this.
- A1C: a blood test that shows your average blood sugar over the past 2 to 3 months. It catches what morning readings miss.
Get both before you start. That baseline is what makes every later number mean something.
Here are the ranges the American Diabetes Association uses:
| Normal | Prediabetes | Diabetes range | |
|---|---|---|---|
| Fasting glucose | Under 100 mg/dL (5.6 mmol/L) | 100 to 125 mg/dL (5.6 to 6.9 mmol/L) | 126 mg/dL (7.0 mmol/L) or higher |
| A1C | Under 5.7% | 5.7 to 6.4% | 6.5% or higher |
A diagnosis takes a repeat test to confirm, so one high reading isn’t a verdict. The trend is what counts.
In the older-adult study, fasting blood sugar had already jumped by week 4, so that’s a good time for your first recheck. An A1C every 3 months covers the longer picture.
MK-677 Blood Sugar Tracker
Log your morning readings below. The tracker shows which range each one lands in and how your numbers are moving compared with your first reading. It saves in your browser, so you can come back tomorrow and add the next one.
Blood Sugar Tracker
Log your fasting glucose each morning. See which range it lands in and where your numbers are heading.
Your readings are saved only in this browser on this device. Nothing is sent anywhere. Ranges follow the American Diabetes Association.
When Your Numbers Say Stop
Here’s how people who use MK-677 carefully read their numbers:
- Creeping up but still under 100 mg/dL: keep logging and watch the trend.
- 100 to 125 mg/dL on repeat mornings, or an A1C of 5.7% or higher: that’s the prediabetes range. Lower the dose or stop, then recheck in a few weeks.
- 126 mg/dL or higher on two mornings, or an A1C of 6.5% or higher: stop, and get checked by a doctor.
MK-677 Dosage and Cycling
Almost every human trial used 25 mg once a day. The 4-week study also tested 2 mg and 10 mg, and the growth hormone response climbed with the dose.
Growth hormone side effects are dose-related, so they tend to climb too. That’s why a lot of users start around 10 mg and only move up if their bloodwork stays clean. I break down the full range in MK-677 dosage: how many mg should you take?
The trials ran MK-677 every day, for up to two years in the longest one. Cycling is something users added. A common pattern is 8 to 12 weeks on, then 4 to 6 weeks off, mainly to give blood sugar and water retention a break.
If you cycle, retest during the off weeks. That’s how you see whether your numbers come back down.
MK-677 vs Injectable Growth Hormone Peptides
MK-677’s big selling point is that it’s a pill, and one dose a day keeps IGF-1 raised around the clock. That steady signal drives both the results and the blood sugar drift.
Injectable peptides work in shorter bursts:
- Ipamorelin hits the same ghrelin receptor as MK-677, but it’s injected and wears off within hours. See MK-677 vs ipamorelin.
- CJC-1295 and sermorelin work through the GHRH receptor, the other switch for growth hormone release. My complete guide to growth hormone peptides covers all of them.
- Tesamorelin is a GHRH analog with its own clinical trial record. See tesamorelin vs MK-677.
If you’re weighing a pill against the hormone itself, I compare them in MK-677 vs HGH.
FAQ
What are the most common side effects of MK-677?
More appetite, water retention, muscle and joint aches, and tingling or numb hands. Higher fasting blood sugar and lower insulin sensitivity are common too, but you only see those on a blood test.
Does MK-677 raise blood sugar?
Yes. In a 2-year trial, fasting blood sugar rose 5 mg/dL on average and insulin sensitivity dropped. In a 4-week study of older adults, average fasting blood sugar went from about 97 to 122 mg/dL.
How long does MK-677 water retention last?
In the 2-year trial, leg swelling was mild and temporary. After stopping, fluid comes off fast: a third of the weight gained in an 8-week trial was gone within a week.
Do MK-677 side effects go away?
Many do. In the 2-year trial, the extra appetite settled within a few months and the swelling passed. Blood sugar is the one to keep testing, since you can’t feel it.
Why does MK-677 make my hands numb?
Fluid around the wrist can press on the nerve that runs into your hand, which causes carpal tunnel symptoms. It’s a known growth hormone side effect and usually improves when the dose is lowered.
Does MK-677 raise cortisol?
Slightly. In the 2-year trial, cortisol rose 1.7 µg/dL on average over the first year. Two shorter studies saw no rise.
Is MK-677 a SARM?
No. MK-677 is a growth hormone secretagogue that works through the ghrelin receptor. SARMs work through the androgen receptor. They get mentioned together because both are popular in fitness circles.
References
- Chapman IM, et al. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-4257. PubMed
- Nass R, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-611. DOI
- Svensson J, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-369. DOI
- Copinschi G, et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278-286. DOI
- Adunsky A, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr. 2011;53(2):183-189. DOI
- Molitch ME, et al. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(6):1587-1609. DOI
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2025. Diabetes Care. 2025;48(Suppl 1):S27-S49. DOI
Stay sharp,
Joe Mars
The Peptide Report
P.S. Logging your numbers and not sure what a trend means? Post it inside the Peptides and Biohacking Hub on Skool. Free community, real protocols, and people actually running this stuff. Join here.
