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Testagen

Gray market

Checked · 21 sources · 10 corrections on this page · No vendors · No affiliates · No one buys a word of it

0 randomized trials published

Preclinical · one report in 20 men · Rossikhin 2011

Gray market · No FDA ruling — not on any list

Sold as a research chemical. Some clinics and pharmacies still supply it; that’s their risk, not a change in the rule.

Bottom line

Khavinson's testicular idea, still on paper. Testosterone itself is an FDA-approved drug. This isn't.

Also called
  • Lys-Glu-Asp-Gly
  • KEDG
  • Testicular Tetrapeptide
  • CAS 1026993-38-3
  • Saint Petersburg Institute of Bioregulation & Gerontology
Category
Peptide — Khavinson Testicular Bioregulator
Sequence
Lys-Glu-Asp-Gly
Length
4 amino acids
Molecular Weight
447.44 g/mol
Target Tissue
Testicular Leydig / Sertoli cells
Route (studied)
Not stated in its studies
Route (sold)
Oral capsules (supplement in Russia); SubQ vials (research)
FDA Status
Not approved; research-only
Russian Status
Dietary supplement (Khavinson tradition)
Developer
V.Kh. Khavinson group
WADA Status
Not specifically listed — prohibited at all times under S0 (no government has approved it for human therapeutic use)
Cost & Access
Research-only

Also for libido & hormones

The other four questions

What does it do? Claimed to raise testosterone by acting on the testis: the 2011 report calls it a “testosterone synthesis inductor” (Rossikhin et al., 2011). No study in testicular cells was found; in a human cell line it entered the nucleus (Fedoreyeva et al., 2011). The only animal studies, in chickens, come from a Khavinson-linked Russian lab (Kuznik et al., 2008, 2011; Pateyk et al., 2013).
Who uses it? Sold in Russia as a dietary supplement for the male reproductive system; one report from clinics in Ukraine and Russia added it to standard treatment for men with chronic prostatitis and low testosterone (Rossikhin et al., 2011). Elsewhere it is sold as capsules or research-chemical vials. Not testosterone replacement therapy, not a TRT substitute.
Does the evidence hold up? Mostly lab and chicken studies. One small clinical report, in Russian, with no randomization, placebo or blinding (Rossikhin et al., 2011). No randomized trial is registered or indexed in PubMed. No human pharmacokinetic study was found.
Bottom line? Khavinson's testicular idea, still on paper. Testosterone itself is an FDA-approved drug. This isn't.

Dosing from the Literature

Published for testosterone: two capsules twice a day with meals for 30 days, each capsule described as holding 0.1 mg of active substance, given to 20 men with chronic prostatitis and low testosterone in one report (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03); the Russian supplement label gives one or two 0.1 mg capsules once or twice a day for a month (Russian product labeling, 2012). Not published: a randomized or placebo-controlled trial.

RouteDoseFrequencyCycle
Oral capsules (men with chronic prostatitis)2 capsules (0.2 mg)Twice a day, with meals30 days, added to standard treatment — Report: 20 men aged 38–49 with chronic prostatitis and low testosterone; 16 men on standard treatment alone were the comparison, with no randomization, placebo or blinding described (Rossikhin et al., 2011)
Oral capsules (Russian supplement)1–2 capsules (0.1–0.2 mg)1–2 times a day, with meals1 month, with a repeat course after 4–6 months advised — Russian product labeling (2012), for adults
Dosing Disclaimer

No dose has been validated in a randomized placebo-controlled trial indexed in PubMed. The one published clinical report gave two capsules, each described as holding 0.1 mg of active substance, twice a day (0.4 mg a day) for 30 days (Rossikhin et al., 2011). The Russian label’s range works out to 0.1–0.4 mg a day (Russian product labeling, 2012). Consult a licensed healthcare provider.

→ Calculator — vial-to-syringe math

What It Is

Testagen is a synthetic tetrapeptide (a chain of 4 amino acids) with the amino acid sequence Lys-Glu-Asp-Gly (single-letter code KEDG) and a molecular weight of 447.44 g/mol. Chemically, it is C17H29N5O9 with CAS registry number 1026993-38-3. It is a member of the family of short synthetic peptides developed by Professor V.Kh. Khavinson and colleagues at the Saint Petersburg Institute of Bioregulation and Gerontology in the 1970s–2010s — a tissue-specific "bioregulator" program that generated dozens of short peptides nominally derived from different organ extracts (Anisimov & Khavinson, Biogerontology 2010; PMID 19830585), each named after the tissue from which its parent-complex was originally isolated. For KEDG that history is mixed: the name and the group’s own tables tie it to the male reproductive system, while the papers that test it in animals describe it as built from anterior-pituitary extracts (Kuznik et al., Bull Exp Biol Med 2011; PMID 22268052).

The Khavinson program built its theoretical foundation on the idea that low-molecular-weight peptides, typically 2–4 amino acids long, can cross cell and nuclear membranes, bind specific DNA sequences or methylated promoter regions, and thereby modulate gene expression in a tissue-specific manner. For Testagen, the proposed target tissue is the testis — specifically the Leydig cells responsible for testosterone biosynthesis and the Sertoli cells that support spermatogenesis. The proposed mechanism is regulation of steroidogenic enzyme transcription.

Testagen is distinct from the more widely known Khavinson thymic bioregulators (Thymalin, Thymogen/Thymagen, Vilon) and from the pineal (small brain gland that makes melatonin) bioregulators (Epitalon, Pineal Peptide Complex). Within the "complete Khavinson system" used in Russian clinical practice, each bioregulator addresses a target organ or tissue class; Testagen occupies the testicular slot. It is less studied than the thymic and pineal peptides, with a smaller published footprint even within the Khavinson research group's own bibliography.

Importantly, Testagen is not exogenous testosterone, not an HCG or gonadorelin analog, and not a direct hormonal agonist at any androgen receptor. Its proposed mechanism operates upstream of hormone secretion — at the transcriptional (at the gene-switching level) regulation of steroidogenic genes — and its expected effects on circulating testosterone in humans are, by the Khavinson framework's own predictions, modest and gradual rather than dramatic and immediate. This framing is critical to avoid conflating Testagen with TRT, HCG, SERMs, or any evaluated male-hormonal therapy.

Who Khavinson was, and what his record supports →

Mechanism of Action

Testagen's proposed mechanism sits within the broader "peptide bioregulation" theoretical framework developed by the Khavinson group. Several elements of this framework remain hypothesis-driven and have not been independently validated by Western structural and functional biology:

  • Direct peptide-DNA interaction (proposed) — The Khavinson group proposes that its short peptides enter cells and nuclei, recognize DNA sequences in gene promoters and regulate DNA methylation (Khavinson et al., Molecules 2021; PMID 34834147). In vitro, Fedoreyeva, Kireev, Khavinson and Vanyushin found fluorescein-labeled KEDG in the nucleus of HeLa cells and reported that it bound preferentially to CAG-containing DNA sequences (Fedoreyeva et al., Biochemistry (Mosc) 2011; PMID 22117547).
  • Leydig cells and testosterone synthesis (claimed) — The 2011 clinical report calls Testagen a “testosterone synthesis inductor” and, citing a 2003 paper from the Khavinson group, says its short peptides act favorably on metabolism in testicular cells (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03). No study of KEDG in Leydig cells, or of the genes and enzymes that make testosterone, was found in PubMed.
  • Sertoli cells and sperm production (untested) — No animal or cell study of KEDG in Sertoli cells or sperm production was found in PubMed.
  • Oral bioavailability (unmeasured) — The 2011 clinical report gave Testagen by mouth, as capsules of a Russian dietary supplement (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03). For that to work, enough intact peptide would have to survive digestion and reach the blood. No pharmacokinetic study of KEDG in people was found in PubMed. The group’s own case for uptake is a computer model: in docking studies, KEDG fit the binding sites of the gut peptide transporter PEPT1 and the amino-acid transporters LAT1 and LAT2 (Khavinson et al., Int J Mol Sci 2022; PMID 35887081; Khavinson et al., Biomolecules 2023; PMID 36979488).
  • Anti-aging (proposed) — The Khavinson group’s peptide theory of ageing holds that ageing changes gene expression and impairs the synthesis of tissue-specific peptides, and that supplying such peptides can help normalize disturbed functions (Khavinson, Neuroendocrinol Lett 2002; PMID 12374906). Mechanistic detail is generic to the broader Khavinson theory rather than specific to testicular biology.
  • Not a direct androgen — No study of KEDG at the androgen receptor was found in PubMed, and no paper found suggests it acts there. The action the Khavinson group proposes for its short peptides is on gene expression (Khavinson et al., Molecules 2021; PMID 34834147).
  • Not a LHRH / GnRH / kisspeptin / HCG analog — No study of KEDG was found at the sites where kisspeptin, gonadorelin and HCG act: the hypothalamus (brain's hormonal control center), the pituitary and the Leydig-cell LH receptor. The chicken studies describe KEDG as built from anterior-pituitary extracts (Kuznik et al., Bull Exp Biol Med 2011; PMID 22268052).
  • Normalizing effect (proposed) — The Khavinson framework holds that its peptides restore disturbed functions toward normal (Khavinson, Neuroendocrinol Lett 2002; PMID 12374906), and the chicken studies describe a normalizing effect of KEDG and the related AEDG on thyroid hormones after removal of the pituitary (Kuznik et al., Bull Exp Biol Med 2011; PMID 22268052). No study of KEDG in the testis was found.

What the Research Shows

The Testagen research base is small, largely Russian-language, and dominated by publications from the Khavinson group or collaborators. Key findings:

  • Khavinson VK, Malinin VV (Karger, 2005) — "Gerontological Aspects of Genome Peptide Regulation." The book-length monograph establishing the theoretical framework within which KEDG and related peptides are framed.
  • Khavinson VK (Neuroendocrinol Lett 2002;23 Suppl 3:11-144) — "Peptides and Ageing." Foundational review of the full Khavinson peptide bioregulator program.
  • Fedoreyeva LI, Kireev II, Khavinson VK, Vanyushin BF — Series of in vitro publications on peptide-DNA binding specificity for short Khavinson peptides; in one, peptides of two to four amino acids inhibited or stimulated the cutting of DNA by eukaryotic endonucleases, depending on the DNA’s methylation (Khavinson et al., Bull Exp Biol Med 2011; PMID 22442805). Two of them name KEDG: fluorescein-labeled KEDG entered the nucleus and nucleolus of HeLa cells and appeared to bind preferentially to CAG-containing DNA sequences in vitro (Fedoreyeva et al., Biochemistry (Mosc) 2011; PMID 22117547), and it bound wheat histones H1, H2B, H3 and H4 (Fedoreyeva et al., Biochemistry (Mosc) 2013; PMID 23581987).
  • Khavinson VK, Bondarev IE, Butyugov AA (Bull Exp Biol Med 2003;135(6):590-592; PMID 12937682) — Epithalon peptide induces telomerase (the enzyme that rebuilds chromosome caps) activity and telomere elongation in human somatic cells — representative of the Khavinson group's published-in-English mechanistic style. Establishes the methodological context within which Testagen's proposed effects would be evaluated.
  • Russian andrology clinical reports — "Efficacy of testosterone synthesis inductor application 'Testagen' in androgenic deficiency in patients with chronic abacterial prostatitis" (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03). 36 men with chronic prostatitis and low testosterone, at clinics in Kharkiv (Ukraine) and Belgorod (Russia): 20 took Testagen for 30 days on top of standard treatment and 16 had standard treatment alone; the report describes no randomization, placebo or blinding. Total testosterone rose from 7.1 to 9.8 nmol/L with Testagen (7.5 with standard treatment alone), and the prostatitis symptom score fell from 16.1 to 9.8 (11.5); adverse events are not reported.
  • Chicken studies (Kuznik group, Chita) — The animal studies in PubMed that name KEDG come from the Chita group of B.I. Kuznik, a frequent Khavinson co-author, and they describe KEDG as built from the amino-acid make-up of anterior-pituitary extracts, not testicular ones. In chickens whose pituitary had been removed, the authors report that 40 days of KEDG or the related AEDG raised thyroid-stimulating hormone and thyroid hormone levels and restored thyroid structure (Kuznik et al., Bull Exp Biol Med 2008; PMID 19024016; Kuznik et al., Bull Exp Biol Med 2011; PMID 22268052), and that KEDG did more than AEDG to restore the thymus (Pateyk et al., Bull Exp Biol Med 2013; PMID 23658898).
  • No Western clinical trials — ClinicalTrials.gov, EU Clinical Trials Register, and UMIN do not list registered controlled trials of KEDG / Testagen. PubMed English-language literature indexed under "testagen" or "KEDG peptide" is sparse.
  • No independent replication in high-evidence journals — None of Testagen's specific steroidogenic claims have been independently reproduced in mainstream endocrinology journals (JCEM, Endocrinology, Nature, Nature Medicine, NEJM, or Lancet-class publications).
Critical Context — Evidence Quality

The Testagen evidence base has three defining features: (1) it is almost entirely from a single research group (Khavinson); (2) it is heavily Russian-language; (3) it has not been independently replicated by Western structural biology, endocrinology, or pharmacology groups. These three features together mean the standard of evidence is meaningfully below the standard applied to FDA-approved or Phase-3-complete compounds. Effects reported in Russian clinical tradition may be real, may be placebo, or may reflect methodological noise. Distinguishing which is which at the individual level is not possible without controlled trials.

Human Data

Summary of Testagen's human evidence:

  • Russian clinical tradition — Multi-decade use of Testagen-class bioregulators in Russian andrology and geriatric practice for age-related androgen decline, chronic prostatitis, and male subfertility. Practice-level "experience" data rather than controlled-trial data.
  • Chronic abacterial prostatitis report — One report, in a Ukrainian journal, compared 20 men given Testagen with standard treatment against 16 given standard treatment alone for 30 days, and found higher testosterone and lower prostatitis symptom scores with Testagen; it describes no randomization, placebo or blinding (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03).
  • No Western randomized placebo-controlled trials — Literature search returns no RCTs of Testagen indexed on ClinicalTrials.gov or the EU Clinical Trials Register.
  • No pharmacokinetic data in humans — Intact KEDG plasma concentrations after oral or SubQ administration in humans have not been published in peer-reviewed form.
  • Safety track record — The one published clinical report does not mention adverse events, and no safety study of Testagen has been published.
  • Self-reported community outcomes — International research-peptide community uses Testagen as an adjunct bioregulator in men's-health stacks. These reports are anecdotal, uncontrolled, and confounded by concurrent TRT, clomiphene, HCG, sleep, exercise, and lifestyle interventions.

The evidence base is exploratory. It does not meet the standard required to call the compound a validated therapy.

Reconstitution & Storage

In Russia, Testagen is sold as a dietary supplement in capsules and tablets; the capsule label lists 0.1 mg of the peptide complex per capsule (Russian product labeling, 2012), the amount of active substance the 2011 clinical report also describes. Research-chemical sellers list it as lyophilized powder in 20 mg vials.

FormStorageReconstitutionShelf Life
Oral capsule, 0.1 mg (Russian supplement)Dry, away from light, 2–25°CNot required5 years — Russian product labeling (2012)
Lyophilized 20 mg vial (research sellers)Powder: −20°C, as two sellers list (one adds: away from light). Mixed: refrigerated, 2–8°C or 4°C2 mL BAC water = 10 mg/mLPowder: 36 months, as one seller lists. Mixed: no period given; one seller says to use it promptly
  • Reconstitution — Reconstitution guides describe adding bacteriostatic water slowly down the inside wall of the vial, then swirling gently.
  • Oral administration — The Russian label gives the capsules by mouth with meals (Russian product labeling, 2012), as the 2011 clinical report did (Rossikhin et al., 2011).

→ Calculator — vial-to-syringe math

Side Effects & Risks

Important

Testagen is a preclinical Khavinson peptide, not testosterone therapy. Consult a licensed healthcare provider.

The one clinical report does not mention adverse events (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03), and no safety study of Testagen was found.

  • Testicular cancer — No study of KEDG in people with testicular cancer was found.
  • Drug-drug interactions — No interaction study was found. The one clinical report gave Testagen alongside tamsulosin and an anti-inflammatory suppository and does not mention adverse events (Rossikhin et al., 2011).
  • Pregnancy and lactation — No study in pregnancy or breastfeeding was found.
  • Pediatric use — No study in children was found.
  • Purity risk — Sold outside Russia as a research chemical, it is not held to drug-quality standards.
  • Limited safety data — With no randomized trial registered or in PubMed, rare or delayed adverse events have not been looked for systematically.

Bloodwork & Monitoring

No trial, label or guideline sets monitoring for Testagen, and the Russian supplement label lists none (Russian product labeling, 2012). The one clinical report measured, before and after 30 days, total testosterone, LH and FSH; three questionnaires (the AMS and Morley scales for androgen-deficiency symptoms and the NIH-CPSI prostatitis score); routine blood and urine tests and blood chemistry; and the prostate, by rectal examination, ultrasound, urine-flow testing and a white-cell count in prostatic fluid (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03).

Commonly Stacked With

No study giving Testagen together with another peptide was found. The one clinical report gave it on top of the clinics’ standard prostatitis treatment, tamsulosin and an anti-inflammatory suppository (Rossikhin et al., Problems of Endocrine Pathology 2011; DOI 10.21856/j-PEP.2011.2.03).

Stacking this? Read the receipt →

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Supportive Nutrition & Context

Legal Status

Current Status — April 2026

Testagen is not approved by the U.S. FDA for any indication. It is not an FDA-approved prescription drug, not a compoundable peptide under section 503A, and not on the FDA's list of nominated bulk substances undergoing active review. In Russia, Testagen-class bioregulators have historically been sold as dietary supplements rather than as prescription pharmaceuticals, consistent with the broader Khavinson product family's regulatory classification.

Testagen is not specifically named on the FDA Category 2 Bulk Drug Substances list, and it was not among the 12 peptides FDA removed from that list in April 2026 (FDA 503A categories list, April 22, 2026). FDA’s April 2026 removals named 12 peptides (BPC-157, TB-500, injectable GHK-Cu, KPV, MOTS-c, Semax, Epitalon, DSIP, LL-37, Dihexa, Melanotan II and PEG-MGF) — Testagen and the related Khavinson peptides are not among them (FDA 503A categories list, April 22, 2026).

Testagen is not named on the 2026 Prohibited List. Because it does not act at the androgen receptor, is not itself testosterone, and has no established performance-enhancing effect in athletes, it does not fit cleanly into S1 (Anabolic Agents) or S2 (Peptide Hormones / Growth Factors). WADA’s S0 clause (non-approved substances) prohibits at all times any pharmacological substance that no other section covers and that no government health authority has approved for human therapeutic use, so it can apply to a peptide sold as a dietary supplement (WADA Prohibited List 2026).

Testagen is sold through research-peptide channels internationally; none of these channels are legitimate medical supply chains. There is no FDA-approved reference product and no legal U.S. compounding pathway.

Cost & Access

Testagen is not approved for human use in the United States. It is available through research suppliers for laboratory research purposes only. In Russia and some other jurisdictions it is sold as a dietary supplement under the Khavinson product family.

U.S. compounding pharmacies cannot compound Testagen under current FDA bulk-substance rules, because KEDG is not on the 503A or 503B compoundable bulk substance lists. Research-chemical channels offer oral capsule and lyophilized injectable presentations; purity, identity, and potency are not assured without independent third-party testing.

Because Testagen is on no FDA list that permits compounding, no regulatory path has opened for legitimate U.S. compounded availability. For the foreseeable future, Testagen will remain a research-only compound in the U.S. regulatory framework.

Estimated regulatory status as of April 2026. Status may change. Kalios does not sell compounds.

References

  1. Khavinson VK. Peptides and Ageing. Neuroendocrinol Lett. 2002;23 Suppl 3:11-144. PMID: 12374906. (Foundational review of the Khavinson peptide bioregulator framework.)
  2. Khavinson VK, Malinin VV. Gerontological Aspects of Genome Peptide Regulation. Basel: Karger; 2005. DOI: 10.1159/isbn.978-3-318-01193-7. (Monograph establishing the theoretical framework for KEDG and related peptides.)
  3. Khavinson VK, Bondarev IE, Butyugov AA. Epithalon peptide induces telomerase activity and telomere elongation in human somatic cells. Bull Exp Biol Med. 2003;135(6):590-592. PMID: 12937682. (Representative Khavinson-group mechanistic paper; establishes the methodological style.)
  4. Fedoreyeva LI, Kireev II, Khavinson VK, Vanyushin BF. Penetration of short fluorescence-labeled peptides into the nucleus in HeLa cells and in vitro specific interaction of the peptides with deoxyribooligonucleotides and DNA. Biochemistry (Mosc). 2011;76(11):1210-1219. PMID: 22117547. (Peptide-DNA interaction evidence for Khavinson-class short peptides.)
  5. Khavinson VK, Popovich IG, Linkova NS, Mironova ES, Ilina AR. Peptide Regulation of Gene Expression: A Systematic Review. Molecules. 2021;26(22):7053. PMID: 34834147. (Lists KEDG as Testagen, “regulation of male reproductive system function”, Table 5.)
  6. Anisimov VN, Khavinson VKh. Peptide bioregulation of aging: results and prospects. Biogerontology. 2010;11(2):139-149. PMID: 19830585.
  7. FDA. Bulk Drug Substances Nominated for Use in Compounding under Section 503A of the Federal Food, Drug, and Cosmetic Act. FDA.gov. Updated 2025–2026 (Testagen / KEDG not listed).
  8. WADA. 2026 Prohibited List. Section S0 (non-approved substances). World Anti-Doping Agency. (Testagen is not named.)
  9. ClinicalTrials.gov, searched October 3, 2026: no registered trial of the KEDG peptide. The one “Testagen” record, NCT02733133, is a testosterone spray of the same name, not the peptide.
  10. Khavinson V, Linkova N, Kozhevnikova E, Dyatlova A, Petukhov M. Transport of Biologically Active Ultrashort Peptides Using POT and LAT Carriers. Int J Mol Sci. 2022;23(14):7733. PMID: 35887081.
  11. Khavinson VK, Linkova NS, Rudskoy AI, Petukhov MG. Feasibility of Transport of 26 Biologically Active Ultrashort Peptides via LAT and PEPT Family Transporters. Biomolecules. 2023;13(3):552. PMID: 36979488.
  12. Khavinson VKh, Fedoreyeva LI, Vanyushin BF. Site-specific binding of short peptides with DNA modulated eukaryotic endonuclease activity. Bull Exp Biol Med. 2011;151(1):66-70. PMID: 22442805.
  13. Fedoreyeva LI, Smirnova TA, Kolomijtseva GY, Khavinson VKh, Vanyushin BF. Interaction of short peptides with FITC-labeled wheat histones and their complexes with deoxyribooligonucleotides. Biochemistry (Mosc). 2013;78(2):166-175. PMID: 23581987.
  14. Rossikhin VV, Hoshchenko YuO, Osipov PG. Efficacy of testosterone synthesis inductor application “Testagen” in androgenic deficiency in patients with chronic abacterial prostatitis. Problems of Endocrine Pathology. 2011;36(2):17-22. DOI: 10.21856/j-PEP.2011.2.03. (In Russian; Kharkiv and Belgorod clinics.)
  15. Kuznik BI, Pateyuk AV, Rusaeva NS. Effect of tetrapeptides Lys-Glu-Asp-Gly and Ala-Glu-Asp-Gly on the structure and function of the thyroid gland in neonatally hypophysectomized chickens. Bull Exp Biol Med. 2008;145(1):104-107. PMID: 19024016.
  16. Kuznik BI, Pateyuk AV, Rusaeva NS, Baranchugova LM, Obydenko VI. Effects of peptides Lys-Glu-Asp-Gly and Ala-Glu-Asp-Gly on hormonal activity and structure of the thyroid gland in hypophysectomized young chickens and old hens. Bull Exp Biol Med. 2011;150(4):495-499. PMID: 22268052.
  17. Pateyk AV, Baranchugova LM, Rusaeva NS, Obydenko VI, Kuznik BI. Effect of peptides Lys-Glu-Asp-Gly and Ala-Glu-Asp-Gly on the morphology of the thymus in hypophysectomized young and old birds. Bull Exp Biol Med. 2013;154(5):681-685. PMID: 23658898.
  18. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011;305(21):2173-2174. PMID: 21632481.
  19. Prasad AS, Mantzoros CS, Beck FW, Hess JW, Brewer GJ. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12(5):344-348. PMID: 8875519.
  20. Koehler K, Parr MK, Geyer H, Mester J, Schänzer W. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009;63(1):65-70. PMID: 17882141.
  21. Testagen® capsules 0.2 g (Russian dietary supplement): product instructions approved by the manufacturer, October 17, 2012, as reproduced in the RLS drug encyclopedia. rlsnet.ru/baa/testagen-34853. Read October 3, 2026. (In Russian.)

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Checked 18 Oct 2026