BRAK LABS Peptide research, plainly written

group

Immune peptides

Three compounds people research for immune function, taken one at a time: what each one is, what has been measured, in whom, and how far apart their evidence bases really are.

Last Reviewed Editorial policy Methodology

Three compounds sit in this group, and they are further apart than any other group on this site. Thymosin alpha-1 is a 28 amino acid peptide first isolated from thymus tissue and now a registered medicine in a number of countries. Thymulin is a nine amino acid thymic hormone that needs zinc to take its active shape. LL-37 is a 37 amino acid antimicrobial peptide, the only cathelicidin the human body makes, cut from the tail of a larger protein called hCAP18.

All three are sold on the same idea, that a peptide the thymus or the immune system makes can be supplied from outside to make immune function work better. What each one has actually been studied for is different: thymosin alpha-1 in hepatitis B, sepsis and COVID-19; thymulin almost entirely as something measured in blood rather than something given; LL-37 as a topical agent for wounds, and as a molecule implicated in the mechanism of several inflammatory diseases.

Each entry below names the population, the design and the endpoint behind every result, and carries the tier of the strongest source that tested that compound for the use it is sold for. Three names in this area are commonly swapped for one another, and the section below sets them apart before the entries begin. The reference list runs to 20 numbered sources: 17 primary papers and reviews, and three agency and registry documents, every identifier checked on 2 August 2026.

Not medical advice

This page reports what has been documented about a compound. It is not medical advice, not a diagnosis, not a dosing protocol, and not a recommendation to obtain or use anything described here. Talk to a licensed clinician about anything concerning your health. Read the full disclaimer.

Reviewed against editorial standards Updated

The compounds in this group

Each row names what the compound is and what its published work covers. The evidence level is the strongest tier of evidence about that compound for the use it is sold for. It is a single figure for a whole entry rather than a claim by claim grading, so an entry may also describe work that is weaker, or that tested a different route or a different molecule, and each of those carries its own citation in the text. Where a compound's own review has been run, its page grades every claim area separately.

Compounds covered on this page, what each one is, and what the published record on it covers
CompoundAlso known asWhat the published work coversWhere it standsEvidence level
Thymosin alpha-1Thymalfasin, Zadaxin, Talpha165 registrations including 8 in phase 3, a published phase 3 in 1,106 people with sepsis that missed its primary outcome, and meta-analyses in hepatitis B and COVID-19Approved in more than 30 countries, unapproved in the United States[Human RCT]
ThymulinZinc-thymulin, FTS, facteur thymique seriqueMouse work on stress and on autoimmune disease, and human studies from the 1980s that measured the body's own thymulin in zinc deficiency. One registry hit, and it gave zincUnapproved, and it carries no modern human record[Animal]
LL-37Cathelicidin, CAP-18, hCAP18 (104-140)61 registrations, most of them measuring the body's own LL-37. Two randomized topical trials, one of which missed its primary outcome, and a large literature placing LL-37 inside the mechanism of psoriasis, rosacea and lupusUnapproved. The interventional work is early, and topical or local[Human RCT]

Thymosin alpha-1, thymulin and thymalin are three different substances

The names collide and vendors carry more than one of them, so it is worth being exact. Thymosin alpha-1 is a 28 amino acid peptide, sold under the international non-proprietary name thymalfasin and the brand name Zadaxin, and it has the largest trial record in this catalog outside the metabolic group. Thymulin is a nine amino acid peptide, originally called facteur thymique serique, whose activity depends on a bound zinc ion [5]. Thymalin is something else again: a calf thymus peptide extract developed in the Soviet Union in the 1970s. The literature on that extract is almost entirely in Russian-language journals [11].

Nothing transfers between them. A phase 3 trial of thymosin alpha-1 says nothing about thymulin, and a Soviet-era report on thymalin says nothing about either. The reason this matters commercially is that the best-evidenced of the three is the one whose name the other two most resemble.

Thymosin beta-4 is a fourth molecule with a similar name and no relationship to any of these. It is covered on the healing and recovery page, where its fragment TB-500 is sold.

Most immune-peptide registrations measure rather than administer

A registration count is the figure most often quoted for a compound in this category, and for immune peptides it is the most misleading. A free-text search of ClinicalTrials.gov for LL-37 on 2 August 2026 returned 61 studies, 17 of them observational [18]. Reading the interventional ones is what settles the question: many give vitamin D, or phenylbutyrate, or a mouthwash, and measure the LL-37 the participant's own body produces as an outcome.

Thymulin is the extreme case. A registry search returns exactly one study, and that study randomized infants to zinc or placebo and measured polio vaccine responses [18]. Thymulin is in the record as a piece of the reasoning, not as something anyone was given.

Thymosin alpha-1 is the opposite, and it is the reason it stands where it does in this catalog: of its 65 registrations, only two are observational, and 33 are phase 2, 8 are phase 3 and 10 are phase 4 [18].

The three compounds, one at a time

Thymosin alpha-1

Also known as Thymalfasin, Zadaxin, Talpha1

Plain-English version: A 28 amino acid peptide first isolated from thymus tissue, given as a medicine in a number of countries and sold in the United States without an approval.

Strongest evidence, and what it covers [Human RCT] Immune modulation in infection and sepsis [1] [2] [3] [4] [18] [19]

Thymosin alpha-1 has the deepest human record of any compound on this site outside the metabolic group. It carries 65 registrations, 33 of them phase 2, 8 phase 3 and 10 phase 4, and only two observational [18]. Its long-standing use is chronic hepatitis B, where a 2008 meta-analysis of four randomized trials in 199 patients compared it against interferon alpha and found the odds ratios favouring interferon at the end of treatment and favouring thymosin alpha-1 six months after it, on virological, biochemical and combined response [2].

The largest single trial is recent and negative. TESTS randomized 1,106 adults with sepsis across 22 centres in China, double blinded and placebo controlled. Death from any cause at 28 days occurred in 23.4 percent of the treated group and 24.1 percent of placebo, a hazard ratio of 0.99, and no secondary outcome separated [1]. Work in COVID-19 is smaller and mixed: an open-label randomized pilot in 49 hospitalized patients reported a faster rise in CD4 cell counts without a significant difference in clinical recovery [3], and a 2023 meta-analysis of eight studies reported lower mortality with high statistical heterogeneity and called for randomized trials to confirm it [4].

Where it stands Thymosin alpha-1 is not an approved drug in the United States: a query of FDA's approved-products data for thymalfasin and for thymosin on 2 August 2026 returned no application [19]. It is registered as a medicine elsewhere, which is why its anti-doping position is genuinely unsettled, since the WADA S0 class covers substances with no current approval by any governmental regulatory health authority [20].

Our takeThe best-evidenced compound in this catalog that is still an unapproved drug in the market selling it. Its biggest and cleanest trial is also the one that found nothing, and that combination is unusual enough to be worth the reader's attention.

Thymulin

Also known as Zinc-thymulin, FTS, Facteur thymique serique

Plain-English version: A nine amino acid hormone made by the thymus that only takes its active shape when a zinc ion is bound to it.

Strongest evidence, and what it covers [Animal] Thymic immune signalling [5] [6] [7] [8] [9] [10] [18]

Thymulin was described in French endocrinology in the 1970s under the name facteur thymique serique, and the finding that made it interesting is that the peptide is inactive until a zinc ion binds to it [5]. That dependence is why most of the human literature about it is nutritional. In 1988, four adults were studied through a period of controlled dietary zinc restriction and repletion, and serum thymulin activity fell during restriction and returned with repletion, in parallel with changes in T cell subsets [6]. A 2021 study compared thymulin activity against other markers of marginal zinc deficiency [8]. Both of those measured the thymulin a person's own thymus produces. Neither gave anyone thymulin.

Where thymulin has been given, it has been given to rodents. In restraint-stressed mice, antibody production against sheep red blood cells fell to about half of the level in unstressed animals, and a three-day course of thymulin at nanogram-per-kilogram amounts returned it close to the normal level, while the same amounts changed nothing in unstressed mice [9]. In a mouse model of severe experimental autoimmune encephalomyelitis, thymulin given into the abdominal cavity alongside or against an inhibitor of NF-kappaB signalling was reported to reduce disease severity and lengthen survival, with the two agents producing no additive effect [10]. A 2004 review collects the wider rodent work on thymulin and the neuroendocrine system [7].

The registry is close to empty. A search of ClinicalTrials.gov for thymulin on 2 August 2026 returns a single study, and it randomized infants in Pakistan to zinc sulfate or placebo and measured polio vaccine seroconversion [18]. Thymulin appears in the reasoning behind that trial rather than in anyone's arm.

One further thing is checkable from the reference list below. Four of the thymulin papers cited here span 1988 to 2021 and share a single author, Dardenne M, with Bach JF on two of them. A small field is a small field, and a group that defines an assay tends to keep using it, but a reader weighing five decades of citations should know how few laboratories they come from. The author lists are printed in full for exactly that reason.

Where it stands Thymulin has no marketing approval in the United States and no monograph, and it was not among the substances the FDA's Pharmacy Compounding Advisory Committee considered on 23 and 24 July 2026. It has no entry on the WADA 2026 Prohibited List and is reached, like any unapproved pharmacological substance, by the S0 catch-all definition [20].

Our takeThe commercial case for thymulin rests on a syllable it shares with thymosin alpha-1. Its own file is two rodent studies, a nutrition literature about the peptide people already make, and a registry entry that gave zinc.

LL-37

Also known as Cathelicidin, CAP-18, hCAP18 (104-140)

Plain-English version: A 37 amino acid antimicrobial peptide, the only one of its family the human body makes, cut from the end of a larger protein.

Strongest evidence, and what it covers [Human RCT] Antimicrobial activity and skin inflammation [12] [13] [14] [15] [16] [17] [18]

LL-37 is the working end of hCAP18, and it does two jobs that pull in opposite directions: it kills bacteria directly, and it drives inflammation. The second half is documented in some of the most cited papers in dermatology. LL-37 binds a person's own DNA and lets it trigger plasmacytoid dendritic cells, a proposed initiating step in psoriasis [12]. Raised cathelicidin and the protease that processes it produce inflammation in mouse skin in a rosacea model [13]. It is a T cell autoantigen in psoriasis patients [14], and citrullinated and native LL-37 specific T cells help autoantibody production in systemic lupus erythematosus [15].

The interventional human work is topical. A phase 2b randomized placebo-controlled trial gave a topical preparation at two strengths to 148 patients with hard-to-heal venous leg ulcers alongside compression, and across the full study population found no significant difference against placebo; a difference appeared in a post hoc subgroup with wounds of at least 10 square centimetres [16]. A separate randomized double-blind trial of an LL-37 cream in diabetic foot ulcers reported a greater increase in granulation index, with no difference in inflammatory markers and none in bacterial colonization at the final measurement [17].

Where it stands LL-37 has no marketing approval anywhere and no US monograph, and it was not among the substances before the FDA's Pharmacy Compounding Advisory Committee on 23 and 24 July 2026. It has no entry on the WADA 2026 Prohibited List and is reached by the S0 catch-all definition covering unapproved pharmacological substances [20].

Our takeThe compound in this group with the most published biology and the most reason for care about it: the same molecule that kills bacteria in a dish is one of the autoantigens named in psoriasis and lupus, and both halves come from the same literature.

What we do not know about this group

None of the three has a completed randomized trial of what it is sold for in this market. Thymosin alpha-1 has been tested in hepatitis B, sepsis and COVID-19, in hospital, in patients with a diagnosis. LL-37 has been tested as a cream on chronic wounds. Thymulin has not been tested in a person at all in the modern registry era. General immune support is the claim, and no trial of any of the three measured it.

Exposure in a healthy person is unknown for all three. The thymosin alpha-1 trials were run in patients with an acute or chronic illness, and no published pharmacokinetic work describes what any of these peptides does in someone who is well.

For LL-37 specifically, the direction of effect is unsettled by design. The published record has it killing organisms and also driving the inflammation of psoriasis, rosacea and lupus, and no study has established what supplying more of it does in a person who is not being treated for a wound [12] [13] [14] [15].

For thymulin, the gap is more basic. The literature that shows thymulin activity tracking zinc status measured the body's own peptide [6] [8]. Whether supplying the peptide from outside reproduces any of that in a person has never been tested, and the rodent studies that gave it used a stress model and an induced autoimmune disease rather than ordinary immune function [9] [10].

What this evidence can and cannot show

These results come from mice in restraint stress and induced autoimmune encephalomyelitis, not from people. An animal model is a deliberate simplification: the injury is created on purpose, the animal is young and healthy, the dose is scaled to body weight in a way that does not translate directly, and the outcome is measured at a fixed point rather than lived with. Cell and tissue work is a further step removed, because the concentrations that produce an effect in a dish are often far above anything a body reaches. Mechanism is a reason to run a trial. It is not a substitute for one, and compounds that looked mechanistically convincing have failed in people many times.

Frequently asked questions

Is thymosin alpha-1 approved in the United States?

No. A query of FDA's approved-products data for thymalfasin and for thymosin on 2 August 2026 returned no approved application [19]. It is registered as a medicine in a number of other countries, which is the source of most of the confusion about its status.

What did the TESTS trial find?

TESTS randomized 1,106 adults with sepsis at 22 centres in China, double blinded against placebo. Death from any cause at 28 days was 23.4 percent with thymosin alpha-1 and 24.1 percent with placebo, a hazard ratio of 0.99, and no secondary or safety outcome differed statistically [1]. It is the largest and cleanest trial in this group.

Are thymosin alpha-1, thymulin and thymalin the same thing?

No, they are three separate substances. Thymosin alpha-1 is a 28 amino acid peptide with a large trial record. Thymulin is a nine amino acid zinc-dependent thymic hormone [5]. Thymalin is a peptide extract of calf thymus developed in the Soviet Union. Reports on that extract are almost entirely in Russian-language journals [11]. Evidence about one is not evidence about another.

How many trials has thymulin had?

One study is returned by a ClinicalTrials.gov search, and it randomized infants to zinc sulfate or placebo and measured polio vaccine responses rather than giving thymulin to anyone [18]. The human literature that does exist measured the thymulin people already make, in the context of zinc deficiency [6] [8].

Why does LL-37 have 61 registrations if it has barely been tested?

Because most of them measure it rather than give it. Seventeen are observational, and many of the interventional ones give vitamin D, phenylbutyrate or a mouthwash and record the participant's own LL-37 as an outcome [18]. The registrations that actually administer LL-37 are few, and they are topical or confined to a single site.

Did the LL-37 wound trials work out?

The phase 2b in 148 patients with venous leg ulcers found no significant difference in healing against placebo across the full study population; a difference appeared only in a post hoc subgroup with large wounds [16]. A smaller randomized trial of an LL-37 cream in diabetic foot ulcers reported a greater increase in granulation index, with no difference in inflammatory markers or in bacterial colonization at the end [17].

Is LL-37 involved in autoimmune disease?

The published record places it inside the mechanism of several. It couples self-DNA to an innate immune sensor in psoriasis [12], it drives skin inflammation in a rosacea model [13], it is a T cell autoantigen in psoriasis patients [14], and LL-37 specific T cells help autoantibody production in lupus [15]. Those papers are about the body's own LL-37.

Which of these is prohibited in sport?

None of the three is named on the WADA 2026 Prohibited List. Thymulin and LL-37 are reached by the S0 catch-all covering pharmacological substances with no current approval by any governmental regulatory health authority, which is prohibited at all times [20]. Thymosin alpha-1 is the genuinely unsettled one, because it holds approvals outside the United States and S0 turns on exactly that.

What would move the grades in this group?

For thymosin alpha-1, a second large trial reading the same way as one of the existing ones, in a population and an endpoint the marketing actually claims. For LL-37, any trial of a systemic route. For thymulin, a first human study of any design in which somebody is given the peptide.

References

  1. Wu J, Pei F, Zhou L, Li W, Sun R, Li Y, Wang Z, He Z, Zhang X, Jin X, Long Y, Cui W, Wang C, Chen E, Zeng J, Yan J, Lin Q, Zhou F, Huang L, Shang Y, Duan M, Zheng W, Zhu D, Kou Q, Zhang S, Liu Y, Yao C, Shang M, Peng S, Zhou Q, Cheng KK, Guan X, TESTS study collaborator group. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025. PMID 39814420 DOI 10.1136/bmj-2024-082583
  2. Yang YF, Zhao W, Zhong YD, Yang YJ, Shen L, Zhang N, Huang P. Comparison of the efficacy of thymosin alpha-1 and interferon alpha in the treatment of chronic hepatitis B: a meta-analysis. Antiviral Res. 2008. PMID 18078676 DOI 10.1016/j.antiviral.2007.10.014
  3. Shehadeh F, Benitez G, Mylona EK, Tran QL, Tsikala-Vafea M, Atalla E, Kaczynski M, Mylonakis E. A Pilot Trial of Thymalfasin (Thymosin-α-1) to Treat Hospitalized Patients With Hypoxemia and Lymphocytopenia Due to Coronavirus Disease 2019 Infection. J Infect Dis. 2023. PMID 36056913 DOI 10.1093/infdis/jiac362
  4. Soeroto AY, Suryadinata H, Yanto TA, Hariyanto TI. The efficacy of thymosin alpha-1 therapy in moderate to critical COVID-19 patients: a systematic review, meta-analysis, and meta-regression. Inflammopharmacology. 2023. PMID 37845598 DOI 10.1007/s10787-023-01354-2
  5. Bach JF, Dardenne M. Thymulin, a zinc-dependent hormone. Med Oncol Tumor Pharmacother. 1989. PMID 2657247 DOI 10.1007/BF02985220
  6. Prasad AS, Meftah S, Abdallah J, Kaplan J, Brewer GJ, Bach JF, Dardenne M. Serum thymulin in human zinc deficiency. J Clin Invest. 1988. PMID 3262625 DOI 10.1172/JCI113717
  7. Goya RG, Brown OA, Pléau JM, Dardenne M. Thymulin and the neuroendocrine system. Peptides. 2004. PMID 15003367 DOI 10.1016/j.peptides.2003.11.002
  8. DiSilvestro RA, Dardenne M, Joseph E. Comparison of Thymulin Activity with Other Measures of Marginal Zinc Deficiency. Biol Trace Elem Res. 2021. PMID 32363520 DOI 10.1007/s12011-020-02159-y
  9. Okamoto M, Morishita M, Setoguchi C, Nakata K. Restorative effect of short term administration of thymulin on thymus-dependent antibody production in restraint-stressed mice. Int J Immunopharmacol. 1993. PMID 8407057 DOI 10.1016/0192-0561(93)90149-s
  10. Lunin SM, Khrenov MO, Novoselova TV, Parfenyuk SB, Glushkova OV, Fesenko EE, Novoselova EG. Modulation of inflammatory response in mice with severe autoimmune disease by thymic peptide thymulin and an inhibitor of NF-kappaB signalling. Int Immunopharmacol. 2015. PMID 25662754 DOI 10.1016/j.intimp.2015.01.021
  11. Khavinson VKh, Morozov VG. [Experimental and clinical study of a new immunoregulator preparation thymalin]. Voen Med Zh. 1982. PMID 7048731
  12. Lande R, Gregorio J, Facchinetti V, Chatterjee B, Wang YH, Homey B, Cao W, Wang YH, Su B, Nestle FO, Zal T, Mellman I, Schröder JM, Liu YJ, Gilliet M. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature. 2007. PMID 17873860 DOI 10.1038/nature06116
  13. Yamasaki K, Di Nardo A, Bardan A, Murakami M, Ohtake T, Coda A, Dorschner RA, Bonnart C, Descargues P, Hovnanian A, Morhenn VB, Gallo RL. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med. 2007. PMID 17676051 DOI 10.1038/nm1616
  14. Lande R, Botti E, Jandus C, Dojcinovic D, Fanelli G, Conrad C, Chamilos G, Feldmeyer L, Marinari B, Chon S, Vence L, Riccieri V, Guillaume P, Navarini AA, Romero P, Costanzo A, Piccolella E, Gilliet M, Frasca L. The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis. Nat Commun. 2014. PMID 25470744 DOI 10.1038/ncomms6621
  15. Lande R, Palazzo R, Gestermann N, Jandus C, Falchi M, Spadaro F, Riccieri V, James EA, Butera A, Boirivant M, Feldmeyer L, Surbeck I, Di Lucca J, Stuber F, Spinelli FR, Botti E, Marinari B, Bianchi L, Pica R, Cerbelli B, Giannakakis K, Auteri SE, Daniels I, Durrant LG, Horstman S, Costanzo A, Romero P, Alessandri C, Conti F, Valesini G, Gilliet M, Chizzolini C, Frasca L. Native/citrullinated LL37-specific T-cells help autoantibody production in Systemic Lupus Erythematosus. Sci Rep. 2020. PMID 32245990 DOI 10.1038/s41598-020-62480-3
  16. Mahlapuu M, Sidorowicz A, Mikosinski J, Krzyżanowski M, Orleanski J, Twardowska-Saucha K, Nykaza A, Dyaczynski M, Belz-Lagoda B, Dziwiszek G, Kujawiak M, Karczewski M, Sjöberg F, Grzela T, Wegrzynowski A, Thunarf F, Björk J, Ekblom J, Jawien A, Apelqvist J. Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: A multicentric prospective randomized placebo-controlled clinical trial. Wound Repair Regen. 2021. PMID 34687253 DOI 10.1111/wrr.12977
  17. Miranda E, Bramono K, Yunir E, Reksodiputro MH, Suwarsa O, Rengganis I, Harahap AR, Subekti D, Suwarto S, Hayun H, Bardosono S, Baskoro JC. Efficacy of LL-37 cream in enhancing healing of diabetic foot ulcer: a randomized double-blind controlled trial. Arch Dermatol Res. 2023. PMID 37480520 DOI 10.1007/s00403-023-02657-8
  18. US National Library of Medicine. ClinicalTrials.gov registry, queried through API v2 on 2 August 2026. Thymalfasin and thymosin alpha 1 each returned 65 studies, of which 33 phase 2, 8 phase 3, 10 phase 4 and 2 observational. Thymulin returned one study, a zinc supplementation trial. LL-37 returned 61 studies, of which 17 observational. ClinicalTrials.gov. 2026. Source document
  19. US Food and Drug Administration. Drugs@FDA approved drug products, queried through the openFDA drugsfda endpoint on 2 August 2026 for thymalfasin as an active ingredient and for thymosin as a generic name. Both queries returned no match. openFDA. 2026. Source document
  20. World Anti-Doping Agency. The 2026 Prohibited List, international standard, effective 1 January 2026. WADA. 2026. Source document