HGH Dosing Protocols in Research: Low vs High Dose Models

Units, Measurement, and Conversion

Research and clinical literature on HGH uses two unit systems that must be clearly understood to interpret dosing data accurately. The international unit (IU) system measures biological activity based on the original pituitary-derived GH bioassay standard. The mass-based system (mg or µg) measures actual peptide mass. These are not interchangeable without a conversion factor, and the conversion factor differs between GH products depending on the specific formulation's potency calibration.

For recombinant human GH (somatropin) — all modern HGH preparations — the accepted standard conversion is:

• 1 mg somatropin ≈ 3 IU
• 1 IU somatropin ≈ 0.333 mg (333 µg)

Examples:

• 2 IU/day ≈ 0.667 mg/day
• 4 IU/day ≈ 1.333 mg/day
• 0.5 mg/day ≈ 1.5 IU/day

Research Note: Some older literature used a 2.7 IU/mg conversion for pituitary-derived GH. All modern recombinant somatropin uses the 3 IU/mg standard. Always verify the conversion factor specified in the product documentation for the specific preparation being used.

The Dose Spectrum: From Replacement to Supraphysiological

HGH dosing in research spans a very wide range — from physiological replacement doses that simply restore deficient levels to supraphysiological doses used in body composition and athletic performance research contexts. Each level of the dose spectrum produces distinct biological effects, distinct IGF-1 profiles, and a distinct adverse effect burden. Understanding where on this spectrum a given research protocol sits is fundamental to designing, interpreting, and comparing research findings.

Physiological Replacement (Low)

• Dose range: 0.1–0.3 mg/day (0.3–0.9 IU/day)
• Target IGF-1: Age-appropriate lower-normal range
• Primary research context: GH deficiency replacement; pituitary insufficiency
• Characteristics: Restores to normal range; minimal adverse effects; GHR sensitivity preserved

Moderate / Somatopause Research

• Dose range: 0.3–0.6 mg/day (0.9–1.8 IU/day)
• Target IGF-1: Age-appropriate mid-normal range
• Primary research context: Aging/somatopause body composition; quality of life research
• Characteristics: Body composition benefits emerge; oedema and glucose effects begin; Rudman study range

High / Body Composition Research

• Dose range: 0.6–1.5 mg/day (1.8–4.5 IU/day)
• Target IGF-1: Upper normal to mildly supraphysiological
• Primary research context: Body composition optimisation; HIV lipodystrophy (Tesamorelin range equivalent)
• Characteristics: Significant fat loss; meaningful lean mass gains; adverse effects common; glucose monitoring essential

Supraphysiological (Very High)

• Dose range: >1.5 mg/day (>4.5 IU/day)
• Target IGF-1: Supraphysiological IGF-1
• Primary research context: Historically used in sports/performance research; GH acromegaly models
• Characteristics: Pronounced body composition effects; high adverse effect rate; significant metabolic risk; acromegalic features with chronic extreme doses

IGF-1 as the Primary Dosing Biomarker

In well-designed HGH research protocols, IGF-1 — not GH itself — is the primary biomarker used to monitor dose adequacy and safety. This is because GH has a short plasma half-life (20–30 minutes for pulsatile endogenous secretion; 3–5 hours for subcutaneous injection absorption) and fluctuates dramatically throughout the day, making spot blood samples unreliable for assessing overall GH axis activity. IGF-1, produced in the liver in direct response to cumulative GH exposure, has a plasma half-life of approximately 15 hours and reflects integrated GH activity over the preceding 24–48 hours — making it a stable, reliable dosing biomarker.

For physiological replacement research in GH-deficient adults, the target IGF-1 range is typically the age- and sex-adjusted middle-to-upper-normal reference range (approximately +0.5 to +1.5 SDS). For anti-aging or body composition research in non-deficient adults, the target is debated but generally kept within the upper normal range to avoid supraphysiological mitogenic signalling. IGF-1 monitoring frequency: monthly for the first 6 months of a protocol, quarterly thereafter once stable target range is achieved.

IGF-1 Reference Ranges by Age (Approximate)

• 20–29 years: Normal 200–450 ng/mL · Low-dose target 200–300 · Body comp target 300–400
• 30–39 years: Normal 160–400 ng/mL · Low-dose target 180–280 · Body comp target 280–380
• 40–49 years: Normal 130–320 ng/mL · Low-dose target 150–250 · Body comp target 250–330
• 50–59 years: Normal 100–270 ng/mL · Low-dose target 130–220 · Body comp target 220–290
• 60–69 years: Normal 80–220 ng/mL · Low-dose target 100–180 · Body comp target 180–240
• 70+ years: Normal 60–180 ng/mL · Low-dose target 80–150 · Body comp target 150–200

Timing of Administration: Evidence and Rationale

Bedtime Administration

The most physiologically rational HGH administration timing is injection shortly before sleep — typically 30–60 minutes before bedtime. This aligns exogenous GH exposure with the period of maximal physiological GH secretion (the first SWS-associated GH pulse), creating a combined endogenous-plus-exogenous GH peak during sleep. However, exogenous GH also suppresses the endogenous sleep-associated GH pulse through negative feedback — so the combined effect is not simply additive. Bedtime dosing minimises GH's insulin-antagonising effects during the post-meal daytime period when insulin sensitivity is most relevant to glucose management.

Morning Administration

Some research protocols use morning administration — injecting GH upon waking, typically in a fasted state. Morning dosing produces a GH peak during the daytime activity period when GH's lipolytic effects are active during a period of physical activity and caloric expenditure, potentially maximising fat mobilisation. The trade-off is increased insulin resistance during the main daytime eating period, which can worsen post-meal glucose control. Morning dosing is more commonly studied in body composition-focused protocols where lipolysis is the primary endpoint rather than GH axis physiological authenticity.

Split Dosing

Some higher-dose research protocols divide the daily HGH dose into two injections — typically half-dose in the morning and half-dose before bed. This approach creates two GH exposure peaks per 24 hours, potentially producing more sustained IGF-1 elevation than a single daily dose. Split dosing is more complex logistically and does not clearly improve body composition outcomes over single daily dosing at equivalent total daily doses in most trials. It is most commonly used in research contexts examining dose-frequency-response relationships rather than in standard clinical protocols.

5 Days On / 2 Days Off Protocol

A popular variation in both clinical and research settings is the "5 days on, 2 days off" protocol — administering HGH on weekdays and omitting doses on weekends. The rationale is that the 2-day break may partially restore GH receptor sensitivity and reduce the cumulative adverse effect burden (particularly fluid retention) compared to continuous daily dosing. Some research suggests the 48-hour washout period allows receptor recovery that improves the metabolic response to the subsequent week's doses. IGF-1 levels remain relatively stable across the on/off cycle at most doses due to IGF-1's ~15-hour half-life providing buffering across 48-hour gaps. This protocol reduces total weekly dose by approximately 28% compared to 7-day dosing, which must be accounted for in dose comparisons.

Individual Variability in GH Response

A critical practical consideration in HGH research dosing is the substantial inter-individual variability in IGF-1 response to a given GH dose. Age, sex, body fat percentage, insulin sensitivity, and genetic polymorphisms in the GH receptor and IGF1 genes all influence the IGF-1 response per unit of GH administered. Older, more obese, and more insulin-resistant subjects typically produce lower IGF-1 responses per IU of GH — requiring higher doses to achieve equivalent target IGF-1 levels compared to younger, leaner, more insulin-sensitive subjects. This variability is the primary reason that IGF-1-guided dosing (adjusting dose based on measured IGF-1 response) is methodologically superior to fixed-dose protocols in research contexts where consistent IGF-1 exposure is required across subjects.

Related Research

• HGH (Somatropin) Research Overview
• HGH vs Peptide-Based GH Stimulation
• HGH & Body Composition Research
• HGH for Anti-Aging: What the Research Shows

References

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