Intranasal sermorelin is not new. It was studied in humans between 1986 and 1993, and the bioavailability came out at 3 to 5 percent of the injected route. Reaching a comparable growth hormone response required roughly 50 times the intravenous dose.
Sermorelin nasal spray is marketed as a modern convenience, but the route was tested decades ago. Sermorelin is chemically GHRH(1-29)-NH2, and intranasal GHRH(1-29)-NH2 was studied in humans between 1986 and 1993. Those trials measured what patients most want to know: nasal absorption was low, with bioavailability of only 3 to 5% [1] compared with the injected route. The research did not stop because the question was unanswered. It stopped because of what the answers showed.
- Intranasal sermorelin bioavailability measured at 3 to 5% versus intravenous [1]
- Reaching a maximal GH response needed roughly 50 mcg/kg intranasally versus 1 mcg/kg intravenously [1]
- A permeation enhancer raised bioavailability only to about 7% [2]
- The one 6-month pediatric trial found the growth effect faded and 3 of 8 children developed anti-GHRH antibodies [3]
- Acute GH release is real. Sustained clinical benefit is what failed
Does It Absorb At All?
Yes, partially, and this is worth stating fairly. In children given intranasal GHRH(1-29)-NH2 at 100 mcg/kg, peak growth hormone reached 28.3 ng/mL at 15 minutes [4]. The nasal route does deliver enough peptide to trigger a measurable pituitary response.
The problem is efficiency. In 30 healthy men, pharmacokinetic study found that absorption through the nasal mucosa was low, with bioavailability of only 3 to 5% [1], and that a maximal GH response required approximately 50 mcg/kg intranasally against 1 mcg/kg intravenously. That is roughly fifty times the dose for a comparable effect.
Attempts to improve it hit a ceiling quickly. Adding sodium glycocholate as a permeation enhancer raised bioavailability to about 7% of intravenous GHRH [2]. Better, still not close to parity.
| Route | Approximate bioavailability | Dose for comparable GH response |
|---|---|---|
| Intravenous | 100% by definition | 1 mcg/kg [1] |
| Subcutaneous injection | High, the standard clinical route | Trial protocols used 10 to 30 mcg/kg [5] |
| Intranasal, plain | [3 to 5%](https://pubmed.ncbi.nlm.nih.gov/8329825/) [1] | ~50 mcg/kg [1] |
| Intranasal with enhancer | [~7%](https://pubmed.ncbi.nlm.nih.gov/2493480/) [2] | Not established for clinical use |
What Happened in the Longest Trial
Acute GH release is a weak endpoint. The question that matters is whether repeated intranasal dosing produces sustained clinical benefit, and one 6-month trial tested exactly that in children with growth hormone deficiency, using 50 mcg/kg three times daily.
The early signal looked promising and then reversed. Growth rate measured by knemometry rose from 0.24 to 0.48 mm per week at 6 weeks, then declined, with no net gain in height velocity across the full 6 months [3]. In the same trial, 3 of 8 patients tested positive for GHRH antibodies at 6 weeks [3], and two patients discontinued.
A low bioavailability can in principle be solved by raising the dose. A response that fades while antibodies develop is a different kind of problem, and it is the finding that most directly undermines a 6-month nasal protocol.
Why Peptides Struggle in the Nose
The barriers are general to the class rather than specific to sermorelin. Nasal bioavailability of peptide and protein drugs is normally less than 1% [6], with three main obstacles: mucociliary clearance sweeps the dose toward the throat within roughly 21 minutes, peptidases in the nasal cavity degrade the peptide, and the nasal mucosa obstructs passage of molecules above about 1,000 Da [6]. Sermorelin is roughly 3,400 Da.
This is not an argument that intranasal peptide delivery cannot work. It can, when a product is engineered for it. Salmon calcitonin nasal spray is FDA-approved, and the commercial 200 IU formulation averaged 1.6% bioavailability versus intramuscular, rising to between 3.9% and 7.9% with a permeation enhancer [7]. Approved intranasal peptides succeed with single-digit bioavailability because the dose and formulation were built and tested around that number.
How to Evaluate a Modern Nasal Product
Current compounded sermorelin nasal sprays are commonly supplied at 1000 mcg/mL. The concentration by itself tells you nothing useful, because the variable that matters is how much peptide crosses the mucosa and reaches circulation, and that depends on formulation, spray volume, and technique.
- Ask what daily delivered dose the product is intended to provide, not just the concentration in the bottle
- Ask what that dose is based on, given that the published intranasal work used roughly 50 mcg/kg per administration
- Ask whether the formulation includes a permeation enhancer, since plain formulations sit at the bottom of the range
- Draw a baseline IGF-1 before starting and retest at 90 days. With an unvalidated route this is the only real check
- Treat a nasal protocol as a distinct protocol, not a milligram-for-milligram substitute for injection
Injection aversion causes people to decline or abandon GH axis therapy entirely. A nasal product that a patient will actually use has a genuine advantage over an injection they will not. That argument is legitimate. It is an adherence argument, not an equivalence argument, and the 90-day IGF-1 is what tells you whether it delivered anything.
Most telehealth platforms only prescribe injectable sermorelin. AgelessRx is the provider in our review set that offers a nasal-spray route, prescribed by licensed clinicians after a physician evaluation.
Frequently Asked Questions
Does sermorelin nasal spray work?
It produces a measurable acute growth hormone response, but inefficiently. Human studies of intranasal GHRH(1-29)-NH2, which is chemically sermorelin, found bioavailability of only 3 to 5% versus the injected route, requiring roughly 50 mcg/kg intranasally to match 1 mcg/kg intravenously [1]. More importantly, the one 6-month trial found the growth effect faded after 6 weeks with no net benefit over the full period [3].
What is the bioavailability of intranasal sermorelin?
Measured at 3 to 5% compared with intravenous administration in 30 healthy men [1]. Adding sodium glycocholate as a permeation enhancer raised it to about 7% [2]. For context, peptide and protein drugs generally show nasal bioavailability under 1% [6], so sermorelin performs somewhat better than the class average while still delivering a small fraction of an injected dose.
Why is sermorelin nasal spray not the standard route?
It was tested and did not hold up. Beyond the 3 to 5% bioavailability, the longest trial gave 50 mcg/kg three times daily to children with GH deficiency for 6 months. Growth rate improved at 6 weeks then declined, with no net height velocity gain, 3 of 8 patients developed GHRH antibodies, and two discontinued [3]. Subcutaneous injection remained the route with reliable, sustained response.
Is nasal sermorelin as good as injections?
No published evidence supports equivalence, and the available data points the other way. All the trial evidence for sustained IGF-1 elevation and body composition change used subcutaneous dosing [5]. The nasal route delivers a small fraction of the dose and has one long-duration trial that failed its endpoint [3]. Treat it as a separate protocol with an unestablished dose rather than a convenient substitute.
What dose of sermorelin nasal spray should I use?
There is no established dose for current compounded products. The published intranasal work used roughly 50 mcg/kg per administration, which is far above typical subcutaneous dosing precisely because so little crosses the mucosa [1]. Products supplied at 1000 mcg/mL do not state a delivered dose. Ask your prescriber what daily delivered dose is intended and what it is based on, and verify the result with a 90-day IGF-1.
Should I choose nasal sermorelin if I hate needles?
It is a defensible choice if injection is a genuine barrier to treating at all, since a therapy you use beats one you abandon. Go in understanding the tradeoff: you are choosing a route with roughly 3 to 5% bioavailability [1] and one long-term trial that failed [3], in exchange for adherence. Draw a baseline IGF-1 and retest at 90 days, because with this route that lab is the only way to know whether anything reached your bloodstream.
References
- Pharmacokinetics of growth hormone-releasing hormone(1-29)-NH2 and stimulation of growth hormone secretion in healthy subjects after intravenous or intranasal administration Acta Paediatrica Supplement, 1993. PMID: 8329825. https://pubmed.ncbi.nlm.nih.gov/8329825/
- Effect of intranasal growth hormone-releasing hormone and corticotropin-releasing hormone administration on growth hormone and cortisol release: improved bioavailability by means of sodium-glycocholate Journal of Clinical Endocrinology & Metabolism, 1989. PMID: 2493480. https://pubmed.ncbi.nlm.nih.gov/2493480/
- Intranasal administration of growth hormone-releasing hormone(1-29)-NH2 in children with growth hormone deficiency: effects on growth hormone secretion and growth Acta Paediatrica Supplement, 1993. PMID: 8329828. https://pubmed.ncbi.nlm.nih.gov/8329828/
- The effects of intranasal insufflation of growth hormone releasing factor analogue GRF 1-29 NH2 on growth hormone secretion in children with short stature Acta Endocrinologica Supplementum (Copenhagen), 1986. PMID: 2877535. https://pubmed.ncbi.nlm.nih.gov/2877535/
- Endocrine and metabolic effects of long-term administration of [Nle27]growth hormone-releasing hormone-(1-29)-NH2 in age-advanced men and women Journal of Clinical Endocrinology & Metabolism, 1997. PMID: 9141536. https://pubmed.ncbi.nlm.nih.gov/9141536/
- Nasal delivery of high molecular weight drugs Molecules, 2009. PMID: 19783956. https://pmc.ncbi.nlm.nih.gov/articles/PMC6254717/
- The bioavailability of intranasal salmon calcitonin in healthy volunteers with and without a permeation enhancer Pharmaceutical Research, 1994. PMID: 8058647. https://pubmed.ncbi.nlm.nih.gov/8058647/
