Sermorelin Dosage in the Research Literature

Sermorelin dosage in published research varies substantially by population and indication. The following doses appear in peer-reviewed trials and the original FDA-approved labeling:

• Pediatric GH deficiency (Thorner 1996, Geref International Study Group, JCEM): 30 mcg/kg subcutaneously at bedtime, daily. This was the FDA-approved Geref dose. In 110 GH-deficient children, this produced height velocity acceleration from 4.1 ± 0.9 cm/yr at baseline to 8.0 ± 1.5 cm/yr at 6 months; 74% of children responded favorably in year one.^[2]
• Pediatric idiopathic short stature (Kirk 1994, Clinical Endocrinology): 20 mcg/kg twice daily subcutaneous for 12 months in 18 pre-pubertal children; height velocity increased from 4.8 ± 0.9 to 7.2 ± 1.6 cm/yr (P=0.001).^[3]
• Pediatric radiation-induced GHD (Ogilvy-Stuart 1997, Clinical Endocrinology): 15 mcg/kg twice daily subcutaneous for 12 months; height velocity improved from 3.3 ± 1.1 to 6.0 ± 1.5 cm/yr (P=0.004) in 9 prepubertal children.^[16]
• Adult aging and body composition (Vitiello 2001, Dialogues in Clinical Neuroscience): 14 mcg/kg (~1 mg) subcutaneously at bedtime daily for 5-6 months; produced ~35% IGF-1 elevation, ~5% lean mass increase, and visceral fat reduction.^[4]
• HIV lipodystrophy (Koutkia 2004, JAMA): 1 mg subcutaneously twice daily for 12 weeks; produced significant IGF-1 elevation and body composition improvements versus placebo.^[10]
• Combination secretagogue protocol (Sigalos 2017, American Journal of Men's Health): 100 mcg sermorelin three times daily subcutaneous (with GHRP-6 and GHRP-2); raised IGF-1 from 159.5 to 239.0 ng/mL (P<0.0001) over a mean 134-day treatment period.^[9]

These are documented research-population doses, not recommendations for any individual.

Native GHRH(1-29)-NH2 plasma half-life is approximately 4.3 ± 1.4 minutes in healthy men via intravenous administration (Soule et al. 1994, Journal of Clinical Endocrinology & Metabolism).^[7] The metabolic clearance rate of native GHRH-(1-29)-NH2 is 39.7 ± 3.9 mL/kg·min. N-terminal enzymatic cleavage is the primary degradation pathway, producing the GRF3-29 metabolite.^[7]

Subcutaneous bioavailability of sermorelin is less than 4%.^[14] Following subcutaneous injection, the compound's biological half-life (GH pulse duration) extends beyond the plasma half-life due to absorption kinetics from the injection depot — the induced GH pulse peaks at 30-60 minutes and returns to baseline within 3-4 hours in pharmacokinetic studies.

A D-Ala2 substitution in the analog backbone doubles the intravenous plasma half-life to 6.7 minutes and halves the metabolic clearance rate to approximately 21 mL/kg·min — demonstrating that N-terminal amino acid modification is the primary degradation-resistance strategy for GHRH analogs.^[7]

Sermorelin has a very short plasma half-life of approximately 4.3 minutes via IV (Soule 1994);^[7] subcutaneous half-life is approximately 8 minutes based on the clinical adverse-event characterization literature.^[14] The GH pulse induced by sermorelin peaks at 30-60 minutes and returns to baseline within 3-4 hours in pharmacokinetic studies. In terms of systemic persistence, the compound itself is cleared within minutes; the downstream GH pulse lasts approximately 3-4 hours, with the biological effects of elevated IGF-1 persisting on a longer timescale determined by IGF-1 half-life (~12-15 hours in serum).

Endogenous GH secretion is highest during slow-wave sleep; evening sermorelin administration is designed to amplify the physiological nocturnal GH pulse.^[8] This timing rationale appears across published protocols: the FDA-approved Geref pediatric dose was administered at bedtime,^[2] and the Vitiello 2001 adult aging study used once-nightly bedtime dosing.^[4]

The Kerkhofs 1993 study (American Journal of Physiology) provided direct mechanistic support: an intravenous GHRH bolus (0.3 mcg/kg) administered during late sleep in healthy young men produced a nearly 10-fold increase in slow-wave sleep in the third REM period. Early-sleep administration increased REM without modifying slow-wave sleep.^[8] The phase-dependence of the sleep effect supports the clinical practice of aligning sermorelin administration with the nocturnal GH pulse rather than morning dosing.

Subcutaneous injection into abdominal, thigh, or deltoid adipose tissue is the route used in clinical trials.^[4][10] The pediatric GHD FDA-approved protocol and all major adult studies used subcutaneous injection exclusively as the primary clinical route. Intramuscular administration has been studied but appears less frequently in the peer-reviewed literature.

Intravenous administration was used in pharmacokinetic characterization studies (Soule 1994, Kerkhofs 1993) but is not a route associated with therapeutic protocols in the published record.^[7][8] Intranasal sermorelin has been studied with lower bioavailability than subcutaneous routes. Oral formulations have not demonstrated clinical efficacy, consistent with the general susceptibility of peptides to gastrointestinal proteolysis.

Acute GH pulse is detectable within 30-60 minutes of injection in pharmacokinetic studies.^[7][8] At the functional level, body composition changes (lean mass, fat mass) and sleep architecture improvements emerge over 4-12 weeks of continuous administration based on the trial data: the Vitiello 2001 study measured outcomes at 5-6 months;^[4] the Thorner 1996 pediatric study showed accelerated height velocity by 6 months;^[2] and the Koutkia 2004 JAMA RCT measured body composition at 12 weeks.^[10] Functional outcomes are duration-dependent; shorter treatment periods may show biomarker (IGF-1) changes before structural or functional changes become measurable.