HGH Fragment 176-191 vs MK-677
Comprehensive side-by-side comparison of mechanisms, dosing, side effects, and research
Also: Frag 176-191, HGH Frag
HGH Fragment 176-191 is exactly what it sounds like: a short tail-end piece of the human growth hormone molecule, amino acids 176 through 191. The idea was to keep the fat-burning part of growth hormone while ditching the parts that raise blood sugar and IGF-1. The bare fragment has never been tested in a controlled human trial. Its modified cousin, AOD-9604, did go through real obesity trials, and the blunt result is that it was very safe but did not produce meaningful weight loss. It is banned in sport by WADA.
Also: Ibutamoren, Nutrobal
MK-677 (ibutamoren) is not actually a peptide, it is a small, orally active non-peptide molecule that mimics ghrelin, your hunger and growth-hormone hormone. Taken as a daily pill, it reliably pushes up growth hormone and IGF-1 levels, which is why it is popular for muscle and recovery. It has been through real human trials but was never approved as a drug, and the trials that mattered most for older adults and Alzheimer's came up short.
Key Comparison Insights
- HGH Fragment 176-191 is categorized as Weight Loss, while MK-677 is Growth Hormone.
- MK-677 has stronger research evidence (Human Trials) compared to HGH Fragment 176-191 (Animal Studies).
Detailed Comparison
| Attribute | HGH Fragment 176-191 | MK-677 |
|---|---|---|
| Category | Weight Loss | Growth Hormone |
| FDA Status | Not FDA Approved | Not FDA Approved |
| Clinical Status | Pre I II III IV FDA | Pre I II III IV FDA |
| Mechanism of Action | This fragment is the C-terminal portion of growth hormone, the segment researchers linked to its effects on fat metabolism. The cleanest early data (Wu and Ng, 1993, rat fat tissue) found the closely related hGH 177-191 matched whole growth hormone at blocking new fat formation (antilipogenic) but had no significant direct fat-breakdown (lipolytic) effect. Later mouse work with AOD-9604 reported more fat oxidation, apparently without binding the growth hormone receptor itself. That is the selling point: because it does not act on the GH receptor, it does not raise IGF-1, does not promote tissue growth, and does not impair glucose handling the way full growth hormone can. Some research points to beta-3 adrenergic signaling in fat tissue, but the human mechanism is not nailed down. | MK-677 is a selective agonist of the growth hormone secretagogue receptor (GHS-R1a), the same receptor the hormone ghrelin binds. By activating that receptor in the pituitary and hypothalamus, it triggers pulses of growth hormone release, which in turn raises IGF-1 (insulin-like growth factor 1) from the liver. Because it copies ghrelin, it also tends to increase appetite, and it can nudge up cortisol levels too. The effect is sustained because it is long-acting and orally available, unlike injectable peptides that mimic ghrelin or growth-hormone-releasing hormone. |
| Common Dosing | 250-500 mcg daily 1-2x daily, fasted | 10-25 mg daily Once daily, often before bed |
| Administration | Subcutaneous injection on empty stomach | Oral |
| Typical Duration | 8-12 weeks | 8-12 weeks or longer |
| Best Time to Take | Before bed or morning (fasted) | Before bed |
Possible Side Effects May vary by individual |
|
|
| Research Summary | The animal data looked promising and the human data deflated it, which is the whole story here. One caveat up front: every human result below comes from AOD-9604, the tyrosine-capped version, not the bare 176-191 fragment sold today. In obese mice (Endocrinology, 2001), both growth hormone and AOD-9604 reduced body-weight gain and increased fat oxidation, without the blood-sugar problems of full GH. A small 12-week phase 2 human study of AOD-9604 generated the early headline, with the 1 mg group losing modestly more weight than placebo. But the larger, better-powered phase 2b trial of roughly 500 obese adults over 24 weeks failed to show a significant weight-loss advantage over placebo, and the developer abandoned obesity development. What survived is the safety record: across about six trials and roughly 900 people, AOD-9604 was as well tolerated as placebo, with no IGF-1 rise and no glucose effects (Journal of Endocrinology and Metabolism, 2013). So the closest human data say safe, and not a meaningful fat-loss drug. | MK-677 has unusually good human data for a compound sold in the gray market, and the data is a mix of clear wins and clear failures. In a one-year randomized trial of 65 healthy older adults (Annals of Internal Medicine, 2008), 25 mg daily raised IGF-1 and increased fat-free mass, basically lean tissue, though much of the early body-weight gain was water and the functional strength benefits were not impressive. In Alzheimer's disease, a large 563-patient, 12-month randomized trial (Neurology, 2008) confirmed it raised IGF-1 but did nothing to slow cognitive decline. Across studies the consistent downsides are increased appetite, fluid retention, and reduced insulin sensitivity (higher blood sugar). So the muscle-and-IGF-1 effect is real and well documented, but MK-677 failed its biggest disease trials, remains unapproved, and is banned in sport by WADA. |
Frequently Asked Questions: HGH Fragment 176-191 vs MK-677
What is the difference between HGH Fragment 176-191 and MK-677?
HGH Fragment 176-191 is a weight loss peptide that hgh fragment 176-191 is exactly what it sounds like: a short tail-end piece of the human growth hormone molecule, amino acids 176 through 191. the idea was to keep the fat-burning part of growth hormone while ditching the parts that raise blood sugar and igf-1. the bare fragment has never been tested in a controlled human trial. its modified cousin, aod-9604, did go through real obesity trials, and the blunt result is that it was very safe but did not produce meaningful weight loss. it is banned in sport by wada. MK-677 is a growth hormone peptide that mk-677 (ibutamoren) is not actually a peptide, it is a small, orally active non-peptide molecule that mimics ghrelin, your hunger and growth-hormone hormone. taken as a daily pill, it reliably pushes up growth hormone and igf-1 levels, which is why it is popular for muscle and recovery. it has been through real human trials but was never approved as a drug, and the trials that mattered most for older adults and alzheimer's came up short. The main differences lie in their mechanisms of action and clinical applications.
Which is better, HGH Fragment 176-191 or MK-677?
Neither is universally "better" - the choice depends on your specific goals. HGH Fragment 176-191 is typically used for weight loss purposes, while MK-677 is used for growth hormone. Always consult with a healthcare provider to determine which may be appropriate for your situation.
Can HGH Fragment 176-191 and MK-677 be used together?
Some peptide protocols combine multiple compounds for synergistic effects. However, using HGH Fragment 176-191 and MK-677 together should only be considered under medical supervision, as both compounds have their own side effect profiles and potential interactions. Research on their combined use may be limited.