Thymulin
Facteur Thymique Serique (serum thymic factor) · FTS · Serum thymic factor · Zinc-thymulin · Nonathymulin
Zinc-dependent thymic nonapeptide studied for T-cell maturation and inflammatory pain.
Typical dose
250 mcg
once daily
Range
100–500
mcg
Half-life
—
see Dosing
Evidence
Early human
Subcutaneous
What it is
Thymulin is a nine-amino-acid hormone secreted by thymic epithelial cells, first isolated in the 1970s as facteur thymique serique. It is unusual in that the peptide on its own is biologically inert: it only folds into its active conformation once it binds a single zinc ion in a 1:1 ratio. Zinc-free thymulin does nothing at all, which matters because vendor material is normally supplied as the zinc-free acetate salt.
Its physiological job is T-cell maturation. It drives differentiation of immature thymocytes, induces T-cell surface markers, and supports IL-2 production and NK activity. Circulating thymulin falls steeply with age as the thymus involutes, and it also falls in zinc deficiency, which is why it comes up in discussions of immunosenescence and longevity.
A second research thread has nothing to do with immunity. At higher doses thymulin and its analogues have strong anti-hyperalgesic and anti-inflammatory effects in rodent pain models, with a clearly biphasic curve: low doses increase pain sensitivity while higher ones suppress it.
The human record is thin and old. It amounts to small uncontrolled 1980s pilots in immunodeficient children and in the elderly. There is no modern controlled trial, no established human dose, and no pharmacokinetic data in people.
How it works
Thymulin binds a zinc(II) ion, which locks the nonapeptide into the conformation its receptors recognise on immature T-cells. Occupying those receptors pushes thymocytes through differentiation, induces T-cell surface markers, and raises IL-2 production and NK cytotoxicity, broadly reproducing part of what an intact young thymus does.
The anti-inflammatory action appears to be a separate mechanism. In rodent models thymulin lowers IL-1 beta, TNF-alpha and nerve growth factor in inflamed tissue and dampens spinal glial activation, which is how it reverses inflammatory hyperalgesia. That effect is biphasic: nanogram doses (5 ng intraplantar or 50 ng intraperitoneal per rat, roughly 0.02-0.2 mcg/kg) increase pain sensitivity in rats, while microgram doses of thymulin or its analogue PAT (1-25 mcg per rat, roughly 4-100 mcg/kg) reduce it.
Dosing
There is no validated human dose. This microgram range is community practice. The rodent anti-hyperalgesic dose is 1-25 mcg per rat i.p. (roughly 4-100 mcg/kg); straight allometric scaling of that gives a human-equivalent 0.6-16 mcg/kg, so 250 mcg in an 80 kg adult sits toward the bottom of the scaled range rather than in the middle of it. Milligram-scale protocols circulating online are almost certainly Thymalin's dose applied to the wrong compound.
Reconstitution calculator
Pre-loaded with Thymulin’s vial size, water volume and typical dose. Change anything.
Typical: 250 mcg · range 100–500
Draw to
10 u
0.1 mL · 250 mcg
Concentration
2.5 mg/mL
25 mcg per unit
Doses per vial
20
Vial lasts
2 weeks 6 days
Draw to 10 units on the barrel.
Once mixed
Refrigerate at 2-8 C and use within about 3-4 weeks.
2 mL of bacteriostatic water into a 5 mg vial gives 2.5 mg/mL, so a 250 mcg dose is 0.1 mL, or 10 units on a U-100 syringe. Aim the water down the vial wall and swirl rather than shaking.
Storage
Before mixing
Sealed lyophilised vials keep about 24 months at -20 C and several months at 2-8 C; the peptide is hygroscopic, so keep it dry.
After mixing
Refrigerate at 2-8 C and use within about 3-4 weeks.
Reported benefits
- ▪Drives maturation and differentiation of immature T-cells
- ▪Supports IL-2 production and NK-cell cytotoxicity
- ▪Restores markers of thymic function that decline with age in animal models
- ▪Strong anti-hyperalgesic and anti-inflammatory effect in rodent pain models
- ▪Small 1980s human pilots reported improved cell-mediated immunity and IgA in immunodeficient children
- ▪Very small molecule with a clean side-effect profile in the limited human exposure on record
Side effects
- ▪Injection-site redness or irritation
- ▪Paradoxical increase in pain sensitivity at doses below the anti-inflammatory threshold, seen in rodents
- ▪Transient fatigue reported anecdotally in the first days
- ▪Theoretical risk of aggravating autoimmune activity via enhanced T-cell output
- ▪Effectively no long-term human safety data at any dose
Do not use if
- ▪Active autoimmune disease, given the T-cell maturational push
- ▪Organ transplant recipients or anyone on immunosuppressive therapy
- ▪Pregnancy or breastfeeding, where there is no data
- ▪Chronic high-dose zinc supplementation, which this peptide requires to be active, can drive copper deficiency (anaemia, neutropenia, myeloneuropathy) - keep elemental zinc at or below about 40 mg/day and check copper on long runs
Evidence level — Early human
Small or early-phase human studies only.
Not approved anywhere; sold as a research chemical, with human exposure limited to small uncontrolled studies conducted decades ago.
Commonly run with
Thymosin Alpha-1
Thymic peptide that tunes T-cell function; licensed abroad as thymalfasin for hepatitis B.
1600 mcg · 2x weekly, spaced 3-4 days apart
Epitalon
Pineal-derived tetrapeptide studied for telomerase activation and circadian regulation.
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BPC-157
Gastric-juice-derived pentadecapeptide studied for tendon, ligament and gut healing.
250 mcg · 1x daily (some split into 2x daily during an acute injury)
Thymulin FAQ
Is thymulin the same as Thymalin?+
No, and vendors conflate them constantly. Thymulin is a defined nine-amino-acid hormone with a known sequence and a molecular weight around 859 Da. Thymalin is a Russian polypeptide extract of calf thymus, an undefined mixture, dosed at 10 mg. If a listing quotes milligram doses for thymulin it is running Thymalin's protocol on the wrong compound.
Do I actually need to take zinc with it?+
Yes. The peptide is only biologically active as the zinc complex, in a 1:1 molar ratio, and most research-grade thymulin ships as the zinc-free acetate. If your zinc status is poor, you are injecting an inert peptide. Standard oral zinc supplementation is sufficient to make the complex available.
How strong is the evidence really?+
Weak by any clinical standard. There are fifty years of rodent immunology and pain work, plus a handful of small uncontrolled 1980s pilots in immunodeficient children and the elderly. There is no randomised controlled trial, no dose-ranging study in adults, and no human pharmacokinetics.
How does it compare to thymosin alpha-1?+
They are both thymic peptides that push T-cell function, but thymosin alpha-1 is licensed in over 30 countries with a large human trial record while thymulin has essentially none. If the goal is immune support with the best evidence behind it, thymosin alpha-1 is the obvious first choice; thymulin is the more experimental option.
Why do some sources say low doses make pain worse?+
Because in rats they do. The hyperalgesic doses are tiny - 5 ng intraplantar or 50 ng intraperitoneal per rat, roughly 0.02-0.2 mcg/kg - while microgram doses of thymulin or its analogue PAT (1-25 mcg per rat, roughly 4-100 mcg/kg) reduce pain instead. That is one reason underdosing is not a conservative choice here in the way it is with most peptides.
References
- 1.Improvement of cellular immunity and IgA production in immunodeficient children after treatment with synthetic serum thymic factor (FTS) — The Lancet (1982) PMID 6124716
- 2.Physiology and therapeutic potential of the thymic peptide thymulin — Current Pharmaceutical Design (2014) PMID 24588820
- 3.Potent analgesic and anti-inflammatory actions of a novel thymulin-related peptide in the rat — British Journal of Pharmacology (2002) PMID 12110619
- 4.Interactions between zinc and thymulin — Metal-Based Drugs (1994) PMID 18476235
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