Editorial note: this article summarises published research on Thymosin Alpha-1, thymalin, thymulin, VIP, oxytocin and glutathione. Baclabs does not sell these compounds or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
Thymosin Alpha-1 is the best-evidenced of a group of peptides sold as immune or systemic “regulators”, and it is the only one with a randomised phase 3 trial of over a thousand patients. The rest ranges from a licensed obstetric medicine (oxytocin) through a neuropeptide that failed its COVID-19 trial (VIP) to a Russian thymic extract with one small study (thymalin) and a skin-lightening injection with almost no controlled data (glutathione).
This article states what has been shown in people for each, the UK legal position, and the reconstitution maths for those supplied as powder. It is the fourth article in the specialized peptides cluster.
Thymosin Alpha-1 (thymalfasin, Zadaxin)
Thymosin alpha-1 (Tα1) is a 28-amino-acid acetylated peptide originally isolated from thymic tissue. Its synthetic form, thymalfasin, is marketed as Zadaxin. It acts as an agonist at Toll-like receptors 2 and 9 on immune cells, promoting T-cell maturation and cytokine production, the basis for its use as an adjunct in chronic viral hepatitis [1].
Licensing and the standard dose
Thymalfasin is authorised in more than 35 countries for chronic hepatitis B and C. The regimen used across most trials and licences is 1.6 mg subcutaneously twice weekly, with single doses of 0.8–6.4 mg studied. It holds US orphan-drug designations for melanoma, hepatitis B, DiGeorge anomaly and hepatocellular carcinoma but has no FDA approval, and no UK or EU marketing authorisation [1]. In the UK it is therefore an unlicensed medicine. The tolerability record is good: the most common adverse effects are local irritation and redness at the injection site [1].
The sepsis trials
Sepsis is where Tα1 has been tested most rigorously. A 2025 pooled analysis of 11 randomised trials in 1,927 patients still reported reduced 28-day mortality (odds ratio 0.73, 95 per cent CI 0.59–0.90), while noting that the higher-quality and multicentre studies showed no significant effect [2]. The decisive study is TESTS, a multicentre, double-blind, placebo-controlled phase 3 trial published in the BMJ in 2025. It randomised adults with sepsis to Tα1 or placebo subcutaneously every 12 hours for seven days. In 1,089 analysed patients, 28-day mortality was 23.4 per cent with Tα1 and 24.1 per cent with placebo, hazard ratio 0.97 (95 per cent CI 0.76–1.24) [3]. The authors concluded there was no clear evidence that Tα1 reduces mortality in sepsis.
Tα1 is sold to consumers as an “immune booster”. No trial supports that use in healthy people.
Thymalin and thymulin
Thymalin is a polypeptide extract of calf thymus developed in the Soviet Union in the 1970s and still registered in Russia. It belongs to the Khavinson “peptide bioregulators”, alongside epithalon (see the bioregulators article). The most recent controlled evidence is a prospective, randomised, single-blind trial in 80 older patients with severe COVID-19 at a single Russian hospital: 36 received thymalin 10 mg intramuscularly daily for 10 days plus standard care, and 44 received standard care plus placebo. The thymalin group had faster recovery of lymphocyte counts and lower hospital mortality [4]. The single-centre, single-blind design and small size leave the result unconfirmed; no thymalin product is licensed in the UK or EU.
Thymulin is different: a nine-amino-acid thymic hormone (facteur thymique sérique) that requires zinc to be biologically active. It has a research literature but no licensed product, no clinical trials of consequence and no human dosing data.
VIP (vasoactive intestinal peptide, aviptadil)
VIP is a 28-amino-acid neuropeptide acting at VPAC1 and VPAC2 receptors: a vasodilator, bronchodilator and anti-inflammatory signal concentrated in the lung. Aviptadil is the synthetic pharmaceutical form.
Its highest-profile test came in COVID-19. The TESICO trial (ACTIV-3b), a randomised, placebo-controlled study in 461 patients with COVID-19 hypoxaemic respiratory failure in the United States, gave intravenous aviptadil as a 12-hour infusion daily for three days at 600, 1,200 and 1,800 pmol/kg on successive days. At day 90 the odds ratio for a better outcome was 1.11 (95 per cent CI 0.80–1.55, p = 0.54) and mortality was 38 per cent with aviptadil versus 36 per cent with placebo. The authors concluded that aviptadil did not improve outcomes [5]. VIP sold online for “lung repair” or “Lyme” has no trial support for those uses; the trial doses were weight-based intravenous infusions in intensive care, not subcutaneous injections.
Oxytocin (Syntocinon) and “oxytocin acetate”
Oxytocin is a nine-amino-acid posterior-pituitary hormone and a prescription-only medicine in the UK. The SmPC for oxytocin 10 IU/mL licenses it for induction and augmentation of labour, incomplete or missed abortion, and prevention and treatment of postpartum haemorrhage. Induction starts at 1–4 milliunits per minute by infusion, increased at 20-minute intervals to a maximum of 20 milliunits per minute; after caesarean or vaginal delivery the dose is 5 IU (8.3 micrograms) by slow intravenous infusion over five minutes. Warnings include uterine hyperstimulation with the risk of rupture, and water intoxication with hyponatraemia after prolonged high-dose infusion [6]. Refrigerated storage at 2–8°C is required.
“Oxytocin acetate” sold as a research peptide is the same molecule as an acetate salt. There is no licensed non-obstetric indication and no evidence base for subcutaneous self-administration.
Glutathione injections
Glutathione is a tripeptide (glutamate-cysteine-glycine) and the main intracellular antioxidant. Intravenous glutathione is licensed in some countries as an adjunct to chemotherapy and in liver disease, but its consumer use is for skin lightening, on the theory that it shifts melanin synthesis from dark eumelanin toward pheomelanin. A 2018 review in Dermatology Practical and Conceptual found that oral and topical glutathione had two and one small trials respectively showing modest, reversible lightening, while the intravenous evidence was limited to a single study with a dubious design and flawed analysis. The Philippine Food and Drug Administration issued an advisory against intravenous glutathione for skin lightening in 2011 [7]. A 2016 letter in the Indian Journal of Dermatology, Venereology and Leprology reached the same conclusion: the safety data are inadequate [8]. In the UK there is no licensed glutathione injection; products offered in aesthetic clinics are unlicensed and their risks are unquantified.
Reconstitution and diluent
Oxytocin is a ready solution. Thymosin alpha-1, thymalin and VIP are lyophilised powders, and the same arithmetic applies: concentration = milligrams in the vial ÷ millilitres of diluent; on a U-100 insulin syringe each unit is one-hundredth of a millilitre.
| Vial | Diluent | Concentration | Per unit (U-100) | Units for licensed-equivalent dose |
|---|---|---|---|---|
| Thymosin α1 5 mg | 1 mL | 5 mg/mL | 50 mcg | 32 units = 1.6 mg |
| Thymosin α1 5 mg | 2 mL | 2.5 mg/mL | 25 mcg | 64 units = 1.6 mg |
| Thymosin α1 10 mg | 2 mL | 5 mg/mL | 50 mcg | 32 units = 1.6 mg |
| Thymalin 10 mg | 2 mL | 5 mg/mL | 50 mcg | 200 units (2 mL) = 10 mg, as in the trial [4] |
Worked example: a 5 mg Tα1 vial with 1 mL of diluent gives 5 mg/mL, so the 1.6 mg dose used in licensed hepatitis regimens [1] is 0.32 mL, or 32 units. A vial drawn from more than once needs a preserved diluent. Bacteriostatic water contains 0.9 per cent benzyl alcohol and is suitable for multi-dose use for up to 28 days after first puncture, as covered in the storage guide; the diluent comparison explains when unpreserved sterile water is appropriate instead. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; see the reconstitution guide for the full method. The hCG article works through a 5,000 IU vial the same way.
Frequently asked questions
Is Thymosin Alpha-1 approved in the UK?
No. Thymalfasin (Zadaxin) is authorised in more than 35 countries for hepatitis B and C, and holds US orphan designations, but it has no FDA, EMA or MHRA marketing authorisation [1]. In the UK it is an unlicensed medicine and can only be supplied on a prescriber’s responsibility for an individual patient.
Does Thymosin Alpha-1 work for sepsis or infection?
The largest trial, TESTS, randomised 1,089 adults with sepsis to Tα1 or placebo every 12 hours for seven days and found 28-day mortality of 23.4 per cent versus 24.1 per cent, hazard ratio 0.97 [3]. Earlier smaller trials were more positive [2]. There is no trial evidence that it prevents infections in healthy people.
What is the difference between thymalin and thymulin?
Thymalin is a crude polypeptide extract of calf thymus from the Russian bioregulator tradition, tested in a small single-blind COVID-19 trial at 10 mg intramuscularly daily for 10 days [4]. Thymulin is a defined nine-amino-acid zinc-dependent thymic hormone with a research literature but no clinical trials or licensed product. Neither is licensed in the UK.
Did VIP help in COVID-19?
No. The TESICO trial gave 461 patients with COVID-19 respiratory failure intravenous aviptadil or placebo for three days and found no improvement in 90-day outcomes (odds ratio 1.11, p = 0.54) and no mortality difference (38 versus 36 per cent) [5].
Are glutathione injections legal in the UK?
There is no UK-licensed glutathione injection. Clinics offering it for skin lightening are supplying an unlicensed product for a use that, according to a 2018 review, rests on a single flawed intravenous study [7]. The Philippine FDA warned against the practice in 2011, and published reviews describe the safety data as inadequate [8].
References
- Thymosin alpha 1: A comprehensive review of the literature. Dominari A, Hathaway D, Pandav K et al. World Journal of Virology, 2020
- Efficacy of thymosin α1 for sepsis: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Cellular and Infection Microbiology, 2025
- The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. Wu J et al. BMJ, 2025
- Peptide Drug Thymalin Regulates Immune Status in Severe COVID-19 Older Patients. Kuznik BI, Khavinson VKh, Linkova NS et al. Advances in Gerontology, 2021
- Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial. Brown SM et al. Lancet Respiratory Medicine, 2023
- Oxytocin 10 IU/ml Solution for infusion: Summary of Product Characteristics. emc, medicines.org.uk
- Glutathione for skin lightening: a regnant myth or evidence-based verity?. Sonthalia S, Jha AK, Lallas A et al. Dermatology Practical and Conceptual, 2018
- Intravenous glutathione for skin lightening: Inadequate safety data. Indian Journal of Dermatology, Venereology and Leprology, 2016
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.