Humanin

Humanin is a 24-amino-acid peptide encoded by mitochondrial DNA, not nuclear DNA. It was discovered in 2001 during a screen for factors that protect neurons from Alzheimer's-related cell death ¹. Cells release it under oxidative, metabolic, and inflammatory stress, where it acts as a built-in survival signal that blocks apoptosis and helps mitochondria recover ².

The modified form S14G-humanin (HNG) has a single amino acid substitution and is roughly 1,000 times more potent than native humanin in cell-protection assays ⁴. HNG is the most studied analog in disease models, while natural variants like P3S are associated with longevity in some mitochondrial DNA lineages ⁵.

Research focuses on conditions in which stressed cells die prematurely: Alzheimer's disease and other neurodegenerative conditions, stroke, heart and kidney injury, diabetes, and reproductive or bone damage. The efficacy evidence is preclinical, meaning it comes from cells and animals. The human data are observational biomarker and exercise studies, not treatment trials ⁴².

Humanin protects cells through two parallel routes. Inside the cell, it binds pro-apoptotic Bcl-2 family proteins called BAX, BimEL, and Bid before they can permeabilize the mitochondrial outer membrane and trigger programmed cell death ⁸. Structural studies show it pulls BAX and Bid into amyloid-like fibers, keeping them away from the mitochondrial surface ¹¹. This is the most replicated mechanism in the field, confirmed in independent laboratories since 2003.

Outside the cell, released humanin signals through the formyl peptide receptor FPR2 and a cytokine-like receptor complex containing gp130 that activates the survival factor STAT3 ³. This arm explains effects on inflammation and insulin sensitivity: central humanin infusion improves whole-body insulin action through hypothalamic STAT3 ¹².

Supporting actions include lowering mitochondrial complex I activity to reduce reactive oxygen species ⁵⁷, activating chaperone-mediated autophagy to clear damaged proteins ⁵⁵, and competing with amyloid-beta at the FPR2 receptor in the brain ⁵². Humanin also binds IGFBP-3, another cell-death signal ⁸.

The activity is context-dependent. In neurons, heart, kidney, and retina it is protective, but in some cancer models the same survival signals support tumor growth ³⁸.

Most functional effects are established in animal models. Human data are mostly observational and link endogenous humanin levels to outcomes, not administered peptide.

Brain. In a triple-transgenic Alzheimer's mouse, three months of intranasal S14G-humanin reduced brain amyloid-beta and improved memory ⁴⁸. In a stroke model, HNG cut infarct size from 56.2% to 26.1% of the brain hemisphere when given before ischemia ⁴⁹. Intranasal humanin reached the brain mainly through trigeminal pathways and improved recovery in a Parkinson's model ⁵⁰. In traumatic brain injury models, it normalized mitochondrial energy production and reduced inflammatory cytokines ³⁵.

Heart. A single HNG dose of 2 mg/kg reduced infarct size and improved ejection fraction after experimental heart attack in mice ¹⁶. Twice-weekly HNG for 14 months reduced age-related cardiac fibrosis and cell death in mice ¹⁷. In human heart failure, lower circulating humanin correlates with higher NT-proBNP and greater 6-month mortality ¹⁹.

Metabolism. Humanin acts centrally and peripherally to improve insulin sensitivity and lower glucose in diabetic rat models ¹². In people, 12 weeks of resistance training raised muscle humanin by 35% in prediabetic men, alongside better glucose control ⁴³, and acute high-intensity intervals raise plasma humanin ⁴². Women with PCOS have lower serum humanin than controls ⁴⁴.

Kidney, lung, bone, and sensory protection. HNG preserved antioxidant defenses after kidney ischemia-reperfusion ¹⁵ and lowered albuminuria in a diabetic nephropathy model ¹⁴. It reduced acute lung injury in mice ²⁸, protected bone growth during glucocorticoid treatment ³¹, and preserved cochlear hair cells against gentamicin damage ⁸⁰.

Reproductive protection. Seminal plasma humanin correlates with sperm concentration and progressive motility in men ²². In rodent models, humanin or HNG reversed SSRI-induced sexual dysfunction ²³, diabetic testicular injury ²⁴, and age-related hypogonadism ²⁵.

Cancer duality. The same anti-apoptotic activity can favor tumor cells. Humanin accelerated triple-negative breast cancer growth and blunted chemotherapy in mice ³⁸, and tumor-derived humanin contributes to glioblastoma chemoresistance ³⁹. This is the main reason the research literature treats active malignancy as a contraindication.

No human randomized trial of exogenous humanin exists. Dose anchors come from rodent in vivo studies and human data on endogenous responses to training and nutrition ⁴².

Preclinical anchors

• Heart attack model, mouse: HNG 2 mg/kg intraperitoneal, single dose at reperfusion, reduced infarct size ¹⁶.
• Kidney ischemia-reperfusion, rat: HNG 2 mg/kg intravenous shortly before reperfusion restored glutathione and superoxide dismutase ¹⁵.
• Aging and cardiac fibrosis, mouse: HNG 4 mg/kg intraperitoneal twice weekly for 14 months reduced fibrosis without reported toxicity ¹⁷.
• Retinal degeneration, rat: HNG 0.4 or 4 mg/kg intraperitoneal twice weekly. Only the 4 mg/kg dose improved visual acuity ²⁷.
• Diabetic tissue protection, mouse: native humanin 4 mg/kg intraperitoneal daily for 15 days improved cardiac, nerve, and testicular injury markers ²⁴.
• Acute lung injury, mouse: HNG 3 to 6 mg/kg intraperitoneal reduced NF-kB and NLRP3-driven injury ²⁸.

Community patterns

Community protocols primarily use the S14G analog HNG rather than native humanin because of its much higher potency ⁴. Typical patterns are HNG 2.5 to 5 mg subcutaneously two to three times per week, or 5 to 10 mg daily to every other day for higher-intensity protocols. Native humanin is used at 10 to 20 mg two to three times weekly. Cycles usually run 8 to 12 weeks with 2 to 4 week breaks. These are community conventions, not validated human doses, and they sit below straightforward allometric scaling from mouse studies ⁴⁷.

Animal routes also include intranasal delivery, which reaches the brain through trigeminal pathways in rodents ⁵⁰. Systemic tissue distribution in rodents is characterized ⁴⁷, but human pharmacokinetic data are not available.

Humanin and HNG are supplied as lyophilized powder for reconstitution before injection. The standard diluent is bacteriostatic water. Because humanin spontaneously forms beta-sheet fibrils and its fibril state is tied to biological activity ⁶, handling matters. Mix by adding diluent slowly down the vial wall and swirling gently rather than vortexing or shaking.

Stability is the practical limit. HNG degrades through oxidation and homodimerization in plain water or PBS, especially at body temperature. In a stabilizing formulation it remains about 95% intact at 4 degrees Celsius through day 28 ⁷. Lyophilized peptide is stored frozen, and reconstituted solution is refrigerated at 2 to 8 degrees Celsius. Solutions that become cloudy or gelled may indicate fibrillar aggregation and should be discarded ⁶.

The calculator below handles diluent volumes and dose measurements for a given vial.

No formal human drug-interaction studies exist for humanin. The findings below are preclinical or mechanistic.

• Cytotoxic chemotherapy. Humanin can protect cancer cells and blunt chemotherapy. It accelerated triple-negative breast cancer growth and reduced doxorubicin efficacy in mice ³⁸, while tumor-derived humanin promoted temozolomide resistance through GP130 signaling in glioblastoma ³⁹. This is the strongest documented interaction concern.
• BCL-2 or BH3-mimetic inhibitors. HNG protected ex vivo rat bone from venetoclax-induced growth retardation ⁷⁹, but the same Bcl-2-family mechanism could reduce antitumor cell death.
• Glucocorticoids. HNG prevented glucocorticoid-induced bone growth impairment without blocking anti-inflammatory effects ³¹, and opposed dexamethasone-induced atrophy in human muscle cells ³⁷.
• SSRIs. Humanin reversed paroxetine-induced sexual and hormonal deficits in male rats ²³. This suggests a potential adjunct role for antidepressant-related sexual dysfunction, but it is unproven in humans.
• GH and IGF-I therapies. GH and IGF-I suppress circulating humanin, so co-administration may lower endogenous humanin tone ¹³.
• Insulin and sulfonylureas. Humanin increases glucose-stimulated insulin secretion in beta cells ⁸³ and improves insulin sensitivity ¹². Additive hypoglycemia is plausible but untested.
• IL-6 or IL-6R-targeted drugs. HNG binds IL-6 receptor alpha and reduces IL-6/STAT3 endothelial injury in sepsis models ²⁹. The clinical relevance is unknown.
• Aminoglycosides. HNG protected cochlear hair cells against gentamicin damage in ex vivo models ⁸⁰.
• Benzodiazepines. Humanin ameliorated diazepam-induced memory impairment in mice ⁸¹.
• Anticoagulants and antiplatelets. A humanin analog attenuated platelet responses in a vascular injury model, though this is abstract-level and unconfirmed ⁷⁷.

Tolerance and cycling are not established by trials. Rodent data include 14 months of twice-weekly HNG without reported toxicity ¹⁷, which suggests frequent daily dosing may not be necessary and long-term exposure is tolerated in mice. Community protocols usually cycle 8 to 12 weeks on with 2 to 4 weeks off, and some use 5 days on followed by 2 days off. These breaks are precautionary, not evidence-driven; no tachyphylaxis data exist.

Reasons cycling appears in community practice include:

• HNG acts through gp130/STAT3, a cytokine-like pathway with feedback controls, so scheduled breaks may let receptor signaling reset.
• Humanin suppresses IGF-I and raises IGFBP-1, while GH/IGF-I suppress humanin ¹³. Continuous exposure could therefore alter the IGF axis over time.
• The pro-tumor signal in breast and brain cancer models argues for bounded exposure ³⁸.

A plateau in response, hypoglycemia symptoms alongside glucose-lowering drugs, or any new cancer diagnosis are reasons the community documents for a break. No human withdrawal or rebound syndrome is reported.

Humanin is often combined with other mitochondrial peptides and repair peptides in community practice. The strongest mechanistic overlaps are with MOTS-c, SS-31, and SHLPs.

• MOTS-c: another mitochondrial-derived peptide. In an atrial fibrillation mouse model, HNG and MOTS-c worked through distinct transcriptional programs and jointly reduced fibrosis and mitochondrial dysfunction ¹⁸.
• SS-31 (elamipretide): a mitochondria-targeting tetrapeptide. An SS31-HNG fusion doubled brain distribution compared with HNG alone and improved cognition in a triple-transgenic Alzheimer's model ⁶⁴.
• SHLP3: synergized with HNG in protecting cochlear hair cells against gentamicin through distinct AKT and AMPK modulation ⁸⁰.
• GLP-1 receptor agonists: no direct interaction data, but complementary glucose-lowering action is expected from mechanism ¹².
• BPC-157 and TB-500: commonly stacked for tissue repair in community protocols, with no reported contraindication in the reviewed literature.

GH secretagogues and IGF-1 analogs work against a humanin-raising protocol because GH and IGF-I suppress endogenous humanin ¹³.

Humanin is not FDA-approved for any indication, and no marketing authorization exists in the United States, EU, UK, or Australia. No human efficacy trial of humanin or HNG has been completed ⁹⁶. The peptide and its analogs are sold as research chemicals rather than medicines.

It is not scheduled under the U.S. Controlled Substances Act, and no country has scheduled it as a controlled substance in the reviewed literature. Humanin is not named on the WADA Prohibited List, and no athlete sanction involving humanin has been published. Because no approved human-use product exists, all supply is research grade.

The regulatory gap is driven by evidence, not by established danger. Rodent pharmacokinetics and tissue distribution are published ⁴⁷, but human safety and efficacy packages do not exist.

Humanin has no human safety database. Rodent studies have used HNG daily or twice weekly for up to 14 months with no reported dose-limiting toxicity ¹⁷. That does not remove the main concerns.

Cancer risk. Humanin can protect cancer cells as readily as healthy cells. It accelerated triple-negative breast cancer growth and blunted chemotherapy in mice ³⁸. Tumor-derived humanin promotes temozolomide resistance in glioblastoma through GP130 signaling ³⁹, and serum humanin is elevated in breast cancer patients ⁷¹. The research literature therefore treats active malignancy and cytotoxic chemotherapy as absolute contraindications.

Glucose lowering. Humanin improves insulin sensitivity and glucose-stimulated insulin secretion ¹². With insulin, sulfonylureas, or other glucose-lowering agents, additive hypoglycemia is a plausible but untested risk.

Stability and aggregation. Native humanin forms amyloid-like fibrils in solution, and HNG degrades via oxidation and dimerization at body temperature in water or PBS ⁶. Refrigeration and prompt use of correctly formulated product are central to avoiding degraded peptide, and cloudy solutions should be discarded.

Cardiovascular and autonomic. Observational hemodialysis data show a U-shaped relationship: both low (below 462 pg/mL) and high (above 778 pg/mL) endogenous humanin are associated with increased cardiovascular events ²⁰. Heart rate variability also follows a non-monotonic pattern across humanin quintiles ⁴⁵. Whether exogenous dosing creates the same risk is unknown.

Special populations. No pregnancy, lactation, pediatric, or human long-term safety data exist. No immunogenicity or human drug-interaction data exist.