HGH Fragment 176-191 — Research Reference

HGH Fragment 176-191 is a synthetic peptide corresponding to the C-terminal 16 amino acids (residues 176–191) of human growth hormone (HGH). It is sometimes referred to as “GH Fragment” or “frag 176-191” in research contexts. The fragment contains the region of HGH that has been investigated for fat-mobilising activity — specifically the amino acid sequence that is proposed to stimulate lipolysis and inhibit lipogenesis in adipose tissue without the anabolic, IGF-1-elevating, or blood glucose effects of full-length growth hormone.

Quick Reference

Overview

The discovery that HGH’s fat-metabolising activity resides in its C-terminal region dates to research in the 1980s and 1990s, when studies identified that specific fragments of HGH retained lipolytic activity without the anabolic properties of the intact hormone. The 176-191 region of HGH — which includes a disulfide bond between Cys182 and Cys189 that is important for structural conformation — was identified as the primary lipolytically active fragment.

The rationale for isolating this fragment is straightforward: full-length HGH stimulates both fat breakdown and muscle growth, elevates IGF-1, and can cause insulin resistance at pharmacological doses. The C-terminal fragment retains the proposed fat-mobilising mechanism while eliminating the anabolic and glucose-regulatory effects, making it a more pharmacologically targeted research compound for fat metabolism.

HGH Fragment 176-191 is closely related to AOD-9604, which is a stabilised pharmaceutical derivative of the same region developed by Metabolic Pharmaceuticals for clinical trials. The two names are sometimes used interchangeably in anecdotal research contexts. Strictly speaking, HGH Fragment 176-191 refers to the unmodified 16-residue peptide, while AOD-9604 incorporates a tyrosine residue and structural modifications that improve stability.

The proposed mechanism of lipolytic activity involves stimulation of β3-adrenergic receptors on adipocytes, activating adenylyl cyclase, elevating intracellular cAMP, and activating hormone-sensitive lipase (HSL) — the enzyme responsible for breaking down stored triglycerides into free fatty acids for energy.

Reported Protocols

Subcutaneous Administration

Subcutaneous injection is the primary reported administration route. Commonly reported doses range from 250 mcg to 500 mcg per day, with the majority of anecdotal accounts describing a single morning injection in a fasted state.

• Single morning injection: 500 mcg upon waking, before food, is the most commonly reported protocol. The fasted state is proposed to maximise lipolytic activity, as elevated insulin attenuates fat mobilisation.
• Split dosing: Some accounts describe 250 mcg administered twice daily — on waking and before a workout or in the early afternoon.
• Pre-workout injection: A single pre-workout injection approximately 30 minutes before exercise is described in some accounts, on the basis that exercise-induced catecholamines may amplify the lipolytic signal.
• Cycle duration: Commonly reported cycles range from 4 to 12 weeks.

Reported Effects

Lipolysis

Research has investigated HGH Fragment 176-191 for its potential role in stimulating lipolysis — the breakdown of stored triglycerides into free fatty acids — in adipose tissue. Preclinical studies using obese animal models reported fat mass reduction with the C-terminal HGH fragment without changes in body weight attributable to lean mass changes. The proposed mechanism involves β3-adrenergic receptor activation and downstream cAMP-mediated activation of hormone-sensitive lipase in adipocytes.

Lipogenesis Inhibition

Research has investigated the fragment for its potential role in inhibiting lipogenesis — the synthesis and accumulation of new fat — in adipocytes. The combination of promoted lipolysis and inhibited lipogenesis is proposed as the basis for the compound’s body composition effects in preclinical research.

No IGF-1 or Anabolic Effects

Research data indicates that HGH Fragment 176-191 does not produce meaningful changes in serum IGF-1 at commonly reported research doses, and does not appear to stimulate the anabolic muscle or bone growth associated with full-length HGH. This represents the key pharmacological distinction from synthetic growth hormone.

No Blood Glucose Disruption

Research has not identified the insulin antagonism or blood glucose elevation associated with full-length HGH administration at commonly reported Fragment 176-191 doses.

Reported Side Effects

Reported side effects in research and anecdotal accounts include the following.

The side effect profile of HGH Fragment 176-191 in anecdotal research accounts is generally reported as mild. The absence of IGF-1 elevation and insulin antagonism is consistent with the absence of the edema, joint pain, and carpal tunnel effects associated with exogenous GH.

Storage & Handling

Lyophilized Powder (Unreconstituted)

• Refrigerator (2–8°C): Preferred; reported stable for 12 months or more
• Room temperature: Short-term stability acceptable; refrigerator strongly preferred
• Freezer: Acceptable for long-term storage; avoid repeated freeze-thaw cycles
• Protect from light and moisture

Reconstituted Solution

• Refrigerator (2–8°C): Use within 4–6 weeks of reconstitution
• Do not freeze reconstituted Fragment 176-191
• Bacteriostatic water is the preferred diluent for multi-dose vials
• Discard if the solution becomes cloudy or shows particulate matter

See the Reconstitution Guide for step-by-step instructions.

Frequently Asked Questions

What is the difference between HGH Fragment 176-191 and AOD-9604? HGH Fragment 176-191 is the unmodified 16-residue C-terminal fragment of human growth hormone (residues 176-191). AOD-9604 is a stabilised pharmaceutical-grade derivative of the same region, incorporating a tyrosine residue at the N-terminus and structural modifications to improve stability. AOD-9604 was developed by Metabolic Pharmaceuticals and underwent clinical trials as an obesity drug candidate. Both compounds are studied for lipolysis and fat metabolism. In anecdotal research contexts, the names are often used interchangeably, though they are technically distinct. See the AOD-9604 profile.

Does HGH Fragment 176-191 increase GH or IGF-1? Research data has not identified meaningful IGF-1 elevation or growth hormone increases attributable to HGH Fragment 176-191 at commonly reported doses. This selectivity for fat metabolism without anabolic hormone elevation is the compound’s defining pharmacological feature relative to full-length HGH.

Can Fragment 176-191 be taken orally? Oral bioavailability of peptides is generally poor due to enzymatic degradation in the gastrointestinal tract. Subcutaneous injection is the standard administration route in research accounts. Oral Fragment 176-191 has not been established to produce equivalent systemic effects to subcutaneous injection in controlled research.

Should Fragment 176-191 be taken fasted? Commonly reported protocols specify administration in a fasted state. The rationale is that elevated insulin — produced in response to food intake — suppresses lipolysis via multiple pathways. Administering a lipolytic agent in the context of high insulin is proposed to reduce its effectiveness.

Related Pages

Goals: Fat Loss · Appetite & Weight Management

Class: Fat Loss & Lipolytic Peptides

References & Further Reading

• Ng FM, et al. (1990). Metabolic effects of a synthetic human growth hormone fragment. Molecular and Cellular Endocrinology, 74(1–2), 75–83. PubMed →
• Heffernan M, et al. (2001). The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following diet in obese mice. International Journal of Obesity, 25(10), 1442–1449. PubMed →
• Heffernan MA, et al. (2000). The effects of a synthetic growth hormone fragment on obesity-related indicators. Endocrinology, 141(1), 422–427. PubMed →