ImmuneFTSSerum thymic factor

Thymulin (FTS)

Q: What is thymulin?

It's a real hormone made by the thymus — a nine-amino-acid peptide originally called 'serum thymic factor' (FTS), isolated from blood in the 1970s. Its biological role is helping T-cells mature and tuning the immune system. It was an important molecule in 1970s–90s immunology.

Q: Why does zinc matter so much for thymulin?

Thymulin is only active when it's bound to zinc — the zinc-free form of the molecule is biologically inactive, because zinc is what folds it into its working shape. This is the most important and most-often-omitted fact: a 'thymulin' product that doesn't deliver the active zinc-bound form isn't delivering the thing that works.

Q: Is there human evidence that thymulin works as a treatment?

Not really. The evidence base is old and overwhelmingly preclinical (animal and test-tube), and there are essentially no modern controlled human trials showing a real clinical benefit from injected thymulin. Its main documented human use has actually been as a blood marker of zinc status, not as a therapy.

Q: Is 'PAT' the same as thymulin?

No. PAT (thymulin-related peptide) is a synthetic analog — a different, man-made molecule. It carries most of the more recent pain-relief and brain-inflammation findings, which should not be transferred onto native zinc-thymulin as if they were the same compound.

Q: Is thymulin banned in sport?

It is not specifically named on the 2026 WADA Prohibited List, but that isn't a clearance — peptide hormones and immunomodulators can fall under broader categories, and this status is an inference rather than a verified ruling. Athletes must verify against the official WADA list and their anti-doping authority.

Thymic nonapeptide hormone · active only when zinc-bound · historic immunology

Thymulin is a genuine hormone made by the thymus — a small nine-amino-acid peptide that was originally called 'serum thymic factor' (FTS) when French immunologists isolated it from blood in the 1970s. Its real biological job is helping T-cells mature and tuning the immune system, and it was a meaningful part of thymus immunology in the 1970s through 1990s. There are two facts that matter most for anyone considering it. The first is that thymulin only works when it is bound to zinc: the zinc-free form of the molecule is biologically inactive, and zinc is what folds it into its active shape. That single nuance is almost always missing from how 'thymulin' is sold — a vial of the bare peptide without the zinc-bound active form is not the same thing. The second is that the evidence is old and almost entirely preclinical. The peak research was decades ago, much of it in animals, and there are essentially no modern controlled human trials showing that injected thymulin produces a real clinical benefit; the main human use of thymulin has actually been as a blood marker of zinc status, not as a treatment. It's also important not to confuse native thymulin with a synthetic lab analog (often called PAT, or 'thymulin-related peptide'), which is what carries most of the more recent pain and brain-inflammation findings — that's a different molecule. The fair framing: real, historically important science, with a critical zinc dependency and no proven human therapeutic outcomes.

The short version

The thymus is the organ where T-cells (a core part of the immune system) are trained. It releases hormones that help that training happen, and thymulin is one of them — a small nine-amino-acid peptide first found in blood in the 1970s and called 'serum thymic factor.' Its real role is in T-cell maturation and immune regulation, and it was an important molecule in the immunology of its era.

The most important thing to understand about thymulin is its dependence on zinc. The peptide only adopts its active shape — and only does its job — when a zinc atom is bound to it. Without zinc, the molecule is inactive. This is why serum thymulin activity drops in people who are zinc-deficient, and it's why the form of the molecule actually matters: a 'thymulin' product that is just the bare peptide, with no attention paid to the zinc-bound active form, is not delivering the thing that works. Vendors almost never address this.

The second thing to understand is how thin the human evidence is. Most thymulin research happened decades ago and was done in animals or test tubes. There are essentially no modern, well-controlled human trials showing that injecting thymulin produces a meaningful clinical benefit — and in fact the main way thymulin has been used in humans is simply as a blood test for zinc status. There's also a naming trap: a synthetic analog (commonly 'PAT' or 'thymulin-related peptide') is responsible for most of the newer pain-relief and brain-inflammation findings, but that is a different, man-made molecule, not native thymulin. The honest read: real and historically important biology, an essential zinc requirement that's usually ignored, and no proven human treatment outcomes.

Molecular identity

Specs

Molecular formula: C₃₃H₅₄N₁₂O₁₅
Molecular weight: 858.9 g/mol (average)
Monoisotopic mass: 858.3832 Da
CAS number: 78922-62-0
PubChem CID: 71300623
Origin: Secreted by thymic epithelial cells

Sequence: pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (<EAKSQGGSN, 9 aa)PMID 827370 (Bach/Dardenne); N-terminal pyroglutamate
Class: Thymic nonapeptide hormone; zinc-dependent immunoregulatorPubChem CID 71300623; PMID 2657247
Active form: Zinc-bound only — the zinc-free (apo) peptide is biologically inactivePMID 2413455; PMID 2657247
Molecular target: No single receptor; zinc-dependent immunoregulator promoting T-cell differentiation/maturationPMID 2657247
Half-life: Not established — human data are biomarker/observational, not interventional pharmacokineticsNot established
Regulatory status: Not FDA-approved; research compound. No controlled human efficacy data for injectable therapeutic useNo approval record

Plain English

Mechanism

Thymulin is produced by the epithelial cells of the thymus and acts as an immunoregulatory hormone, described in the classic literature as a 'lymphocyte-differentiating thymic nonapeptide.' Its core role is in promoting T-cell differentiation and maturation and in tuning immune responses — fitting the thymus's job as the organ where T-cells develop.

The defining mechanistic feature is zinc-dependence. Thymulin has to bind a zinc ion to fold into its biologically and antigenically active conformation; the zinc-free (apo) form is inactive. Zinc binding is what creates the active epitope on the molecule. This is not a minor detail — it is the difference between an active hormone and an inert peptide, and it directly explains why serum thymulin activity falls in zinc deficiency and can be restored by zinc.

Two cautions on mechanism. First, the broader claims of a thymulin–neuroendocrine feedback loop come mostly from review-level discussion rather than tightly established primary mechanism, so they should be read as plausible context, not settled fact. Second — and importantly — much of the more recent anti-inflammatory and analgesic mechanistic work (for example signaling through the α7-nicotinic acetylcholine receptor) was done with a synthetic thymulin-related peptide analog (PAT), not native zinc-thymulin. Those findings should not be transferred onto native thymulin as if they were the same molecule.

Sources:PMID 827370 PMID 2413455 PMID 3711109

Why people reach for it

Potential benefits

Thymulin is a genuine thymic hormone with real historical importance — here is what draws people to it, kept honest about old, preclinical evidence and one non-negotiable catch (zinc).

A real thymic immune hormone, not a designer peptide — Thymulin is an actual hormone the thymus makes, central to T-cell maturation and a meaningful part of 1970s–90s immunology — its appeal is that the underlying biology is genuine, not invented marketing.
The T-cell maturation angle — Its documented role is helping T-cells mature and tuning immune responses, which is why people reach for it for immune-resilience goals — though the human evidence is old and mostly preclinical, not proven therapy.
A well-defined, fully verified molecule — It is a precisely sequenced nonapeptide with confirmed identifiers — so unlike the murkier extracts in this family, what the molecule is chemically is not in dispute.
A tight, biochemically-grounded zinc story — Thymulin's activity is literally switched on by zinc, giving it the clearest cofactor rationale in the library — appealing to people who want a mechanism they can actually act on (ensure zinc sufficiency).
Pairs cleanly with the rest of the thymic family — Because it works at the T-cell maturation stage, it slots alongside other thymic peptides like Thymosin Alpha-1 that act downstream — a coherent immune-axis pairing rather than the same lever twice.

Sources:PMID 827370 PMID 2413455 PMID 3262625 PMID 24588820

What people reach for Thymulin for, drawn from its genuine thymic biology and how it's used — not proven human outcomes or medical claims. The human evidence is old and largely preclinical, and the bare peptide is inactive without zinc.

Implied timing

Best time to dose

Implied best time

Anytime (consistent)

Time of day isn't critical for Thymulin — pick a consistent daily time and hold it; zinc sufficiency matters far more than the hour.

Thymulin has no established human pharmacokinetics and no half-life on record, so there is no clearance curve to time a dose against — day-to-day consistency matters more than the exact hour.
The single biggest variable is not timing but zinc: thymulin is inactive unless it is zinc-bound, so adequate zinc status (see Cofactors) determines whether a dose does anything at all — far outweighing time of day.
As an immune/thymic peptide, a mild evening lean is reasonable on the logic that immune consolidation and repair run overnight — but this is a soft rationale, not a thymulin finding, and any consistent time is fine.

No study establishes an ideal time of day for thymulin — this is reasoned from how it's used and general immune rhythm, not from data. As a rule of thumb most peptide dosing lands in the midday-to-evening window; for thymulin any consistent time works, with at most a mild evening lean.

Sources:PMID 3262625

How to run it

Dosing & protocol

Thymulin is dosed here as a subcutaneous injection — the form sold as a research peptide and the route the on-page calculator is built for. It has no established human dose: no human interventional trial has been located in PubMed or ClinicalTrials.gov (as of May 2026). The ranges below are therefore not a convention drawn from a human regimen — they are a placeholder derived from the calculator defaults. Read this section as the practical framework for how thymulin would be administered if a researcher chose to use it, with the full understanding that no validated human dosing exists.

No established human dose exists for thymulin. Its human literature is observational only (thymulin as a zinc-status biomarker), not interventional. The figure in the calculator is a neutral research placeholder, not a therapeutic recommendation. Thymulin is not an FDA-approved drug.

Dose — no established human dose

Unlike most peptides in this library, thymulin has no community-convention dose drawn from human use — because there are no modern human trials to draw from.

Route:: Subcutaneous injection into abdominal or thigh fat — consistent with how it would be handled as a research peptide, and the route the calculator is calibrated for.
Dose reality:: No human dose range exists in the published literature. The calculator placeholder of 1,000 mcg is a neutral default only, not a validated starting point. Anyone referencing a specific thymulin dose from a vendor or forum is citing extrapolation, not evidence.
Zinc-bound form caveat:: A milligram or microgram figure for 'thymulin' is biologically meaningless unless it refers to the active zinc-bound form. The bare (apo) peptide is inactive. If the zinc-bound status of a product is not confirmed, the dose figure is irrelevant.

Subcutaneous administration

Thymulin is injected into subcutaneous fat; site and timing are the actionable choices.

Injection site:: The abdomen (staying a couple of inches clear of the navel), the love-handle area, or the outer thigh. Rotate sites between doses so one spot isn't used repeatedly — this prevents local irritation and lipohypertrophy.
Measuring the dose:: Drawn on a U-100 insulin syringe from the reconstituted vial; the reconstitution card below converts the placeholder dose to syringe units (e.g. 1,000 mcg = 20 IU at the standard 5 mL mix), and the calculator does it for any vial size.
Time of day:: No timing data exists for thymulin — see Best time to dose above. Time of day isn't critical; a consistent daily time matters more than the hour (and zinc sufficiency matters far more than either), with at most a mild evening lean on immune-rhythm logic.
Food window:: Subcutaneous injection is independent of meals — food does not affect absorption at the injection site.

Cycle & washout

No cycle length is established for thymulin. The framework below is the general convention applied to immune-modulating peptides.

Standard cycle:: 4–8 weeks of use, then reassess. This matches the typical thymic-peptide convention used for Thymosin Alpha-1 and related compounds in the same family.
Washout:: 2–4 weeks off. Given the absence of human pharmacokinetic data, the off-period is precautionary — thymulin's actual clearance time in humans is unknown.
Zinc status first:: Before and during any thymulin use, zinc sufficiency is the prerequisite (see Cofactors). Without adequate zinc, the molecule is inactive — cycling the peptide without addressing zinc status produces no active hormone.

Reconstitution at a glance

The on-page calculator does this live; the quick reference for a 10 mg vial:

Mixing:: 10 mg vial + 5 mL bacteriostatic water = 2,000 mcg per mL. On a 100-unit (1 mL) insulin syringe: 500 mcg = 25 IU · 1,000 mcg = 50 IU · 1,500 mcg = 75 IU · 2,000 mcg = 100 IU.
Why 5 mL:: The higher dilution spreads doses across more syringe units, reducing measurement error at low microgram amounts.

Sources:PMID 827370 PMID 3262625 PMID 2413455

Substrate the signal needs

Nutritional cofactor precision

Thymulin has one cofactor that is not optional and not reasoned — it is required by the molecule's own chemistry: zinc. This is the clearest cofactor case in the library. Beyond zinc, the T-cell axis thymulin acts on is supported by a small set of immune-nutrition essentials.

Zinc is established biochemistry (primary sources: PMID 2413455, PMID 2657247). Vitamin D, selenium, and copper-balance are reasoned from what the T-cell axis needs — not thymulin-specific cofactor studies. Supplement doses are common sufficiency ranges, not thymulin-trial findings.

Zinc — required for thymulin to be active at all

This is not 'zinc supports thymulin' — it is that thymulin is not the active molecule until a zinc ion binds it. The apo-peptide (zinc-free form) is biologically inert.

Mechanism:: Zinc binding folds thymulin into its active conformation and creates the antigenic epitope the immune system recognizes. Without bound zinc, the peptide is inactive — serum thymulin activity falls in zinc deficiency and is restored by zinc repletion. This is primary-source biochemistry, not a wellness extrapolation.
Protocol integration:: 15–30 mg elemental zinc daily (picolinate or bisglycinate for absorption) — dosed to sufficiency, not a loading strategy. Pair with 1–2 mg copper bisglycinate daily to prevent copper depletion from ongoing zinc use. Test serum zinc before starting; if you are already deficient, correct that first — using thymulin while zinc-deficient delivers an inactive peptide.
Timing:: Take zinc with a small meal (reduces nausea); separate from iron supplements by 2+ hours. Morning or with lunch is the standard convention.

Vitamin D + Selenium — supporting the T-cell axis thymulin acts on

Thymulin promotes T-cell maturation and differentiation. Both vitamin D and selenium are established regulators of T-cell function and immune defense — so they support the output of thymulin's action.

Vitamin D mechanism:: Vitamin D receptors are expressed on T-cells and dendritic cells; deficiency impairs T-cell activation and differentiation — the same process thymulin facilitates. The goal is sufficiency (serum 25-OH-D in the 40–60 ng/mL range), not supraphysiologic loading.
Vitamin D protocol:: 2,000–5,000 IU vitamin D3 daily with a fat-containing meal (it is fat-soluble). Dose to a measured blood level; recheck at 3 months.
Selenium mechanism:: Selenium is essential for selenoprotein-based antioxidant defense in immune cells (glutathione peroxidase, thioredoxin reductase). Adequate selenium keeps the immune environment in which thymulin-matured T-cells operate from being oxidatively stressed.
Selenium protocol:: 100–200 mcg selenium daily (selenomethionine or high-selenium yeast). Do not exceed 400 mcg/day — selenium has a narrow therapeutic window and excess is toxic.

Mitigate — very low side-effect cost

Thymulin itself has essentially no characterized side-effect profile in humans (no modern controlled safety data), so there is no well-defined cost to mitigate. The primary mitigation target is zinc-induced copper depletion.

Copper balance:: Ongoing zinc supplementation depletes copper over weeks to months. Include 1–2 mg copper bisglycinate daily any time zinc is used continuously. Copper deficiency from unchecked zinc supplementation causes anemia and neurological symptoms — this is a real, documented interaction.
Selenium ceiling:: Stay below 400 mcg/day selenium total. Chronic selenosis (excess selenium toxicity) causes hair loss, nail changes, and neuropathy — symptoms that emerge slowly and are often attributed to other causes.

Combinations + timing

Stacking notes + timing windows

Thymulin sits in the thymic-peptide family — compounds that act on thymus-related immune signaling. The best stacks pair it with other members of that family who work on different molecules or different immune arms, or add a systemic healing layer alongside the immune reset. Stacking two thymic peptides targeting the exact same T-cell differentiation step would push the same lever twice — the pairings below each bring a distinct contribution.

Thymic-family combinations are reasoned from complementary mechanisms and community convention — no stack involving native thymulin has been studied head-to-head in humans. Native thymulin itself has no controlled human efficacy data, so any stack is doubly convention. The zinc-cofactor prerequisite applies to all combinations: none of these pairings work if thymulin is inactive from zinc deficiency.

Thymulin + Thymosin Alpha-1

The two best-characterized thymic peptides — same family, different molecules, different primary actions.

Why it works:: Thymulin promotes T-cell maturation from thymic precursors; Thymosin Alpha-1 acts downstream to enhance T-cell activity and cytokine output from already-differentiated cells. The two operate at sequential stages of the T-cell lifecycle rather than the same step — making this the most mechanistically coherent pairing in the thymic family. Note that Thymosin Alpha-1's most rigorous human trial (in hepatitis B) was null; its evidence is mixed, but it is the better-studied of the two.
The protocol:: Thymulin at the calculator placeholder dose subcutaneously, alongside Thymosin Alpha-1 on its own typical schedule (commonly ~1.5 mg subcutaneously twice weekly). Both are thymic-family peptides used on a 4–8 week cycle with a washout break.
Outcome:: Reached for in contexts of immune dysregulation where both T-cell maturation (thymulin's territory) and downstream T-cell activation (Thymosin Alpha-1's territory) are implicated — such as chronic immune suppression or post-illness immune reset.

Thymulin + Thymogen

Two thymic-family molecules from different structural classes — thymulin is a nonapeptide, Thymogen (Glu-Trp) is a dipeptide.

Why it works:: Thymogen is a short synthetic dipeptide (Gamma-D-glutamyl-L-tryptophan) framed as a thymic-hormone activator — it is postulated to upregulate endogenous thymic signaling rather than directly substituting for a specific thymic hormone. Pairing it with thymulin means one compound (thymulin, if zinc-bound and active) provides the nonapeptide hormone signal directly, while the other (Thymogen) is intended to amplify endogenous thymic activity. Different structural approach, same target territory.
The protocol:: Community use of Thymogen typically follows short cycles (1–2 mg subcutaneously daily for 10-day courses). Thymulin would run alongside on its own placeholder schedule. Both are short-cycle compounds.
Outcome:: A thymic-saturation approach used in the community for general immune support and recovery — two molecules from the same family, different structures, covering the thymic-signaling space from different angles.

Thymulin + BPC-157

Pair an immune-reset signal with a systemic healing and tissue-repair compound — different systems, complementary goals.

Why it works:: BPC-157 promotes tissue repair, gut-barrier healing, and angiogenesis (growth of new blood vessels into healing tissue) — a systemic recovery signal. Thymulin's focus is immune maturation and T-cell regulation. The two address different biological layers simultaneously: one tunes the immune system's cellular training, the other promotes tissue and systemic recovery. Different levers, not the same one twice.
The protocol:: BPC-157 250–500 mcg subcutaneously once daily, alongside thymulin on its own placeholder schedule. BPC-157 is typically run on a 4–6 week cycle. The zinc-cofactor prerequisite for thymulin applies here too — confirm zinc sufficiency before adding thymulin to any stack.
Outcome:: Reached for in post-illness recovery or after inflammatory injury where both immune normalization and tissue repair are relevant goals simultaneously — immune reset + structural healing running in parallel.

Reconstitution math

Reconstitution calculator

Calculated for a 1 mL U-100 insulin syringe (100 units/mL).

Peptide per vial

BAC water added

Desired dose

Units per dose

Draw to this mark on a U-100 syringe

Volume per dose: 0.2 mL
Doses per vial: 10
Concentration: 5 mg/mL

One vial lasts

Daily: 10 days
Every other day: 20 days
5×/week: 14 days

Research use only. Not for human consumption. Outputs are reference values based on research literature — verify all measurements independently.

From the studies

Side effects from research

There is essentially no modern controlled human safety data for thymulin used as a therapeutic, because there are no modern controlled human efficacy trials and no established dose. The human literature is observational (thymulin as a zinc-status biomarker), which does not characterize the safety of injecting the peptide.

Much of the more recent biological-effect data — including effects that would be relevant to a safety discussion — comes from the synthetic PAT analog rather than native thymulin, so it cannot be assumed to describe native thymulin's safety. On top of that, gray-market sourcing adds the usual identity and purity risks, compounded here by the uncertainty of whether the active zinc-bound form is even present.

The honest summary: thymulin is a real thymic hormone with genuine historical importance, but its safety as an injected supplement in humans is simply uncharacterized — there are no proven immune-boosting outcomes and no modern human safety surveillance to point to.

Sources:PMID 24588820

As reported in literature

Research dosing ranges

There is no human dose for thymulin — the table below is historical and preclinical, shown to illustrate the science, not to suggest a regimen. Two things frame all of it: thymulin is inactive without bound zinc, and most recent pain/inflammation findings belong to a synthetic analog (PAT), not native thymulin. No milligram or microgram dose is given because none is established for humans.

Dose	Route	Model	Outcome	Sources:
Not applicable	Lab (isolation)	Original isolation & sequencing (Bach/Dardenne 1976, C R Acad Sci)	Thymulin (then 'serum thymic factor', FTS) isolated from serum and sequenced by Edman degradation as a thymic nonapeptide — the founding identification	PMID 827370
Not applicable	In vitro (molecular)	Zinc-dependent epitope (1985, PNAS)	Demonstrated that thymulin's active/antigenic epitope is zinc-dependent — the zinc-free peptide is inactive; zinc binding creates the active form	PMID 2413455
Observational	Human (biomarker)	Serum thymulin in human zinc deficiency (Prasad 1988, J Clin Invest)	Serum thymulin activity tracks zinc status — it falls in zinc deficiency and is restored by zinc; thymulin's main human use is as a zinc-status marker, not a treatment	PMID 3262625
Experimental	Animal (analog)	PAT analog — analgesic/anti-inflammatory in rat (2002, Br J Pharmacol)	ANALOG, not native thymulin: the synthetic thymulin-related peptide (PAT) showed analgesic/anti-inflammatory effects in rodents — illustrative of analog biology, not a native-thymulin human result	PMID 12110619

Quick answers

Frequently asked

What is thymulin?

It's a real hormone made by the thymus — a nine-amino-acid peptide originally called 'serum thymic factor' (FTS), isolated from blood in the 1970s. Its biological role is helping T-cells mature and tuning the immune system. It was an important molecule in 1970s–90s immunology.

Why does zinc matter so much for thymulin?

Thymulin is only active when it's bound to zinc — the zinc-free form of the molecule is biologically inactive, because zinc is what folds it into its working shape. This is the most important and most-often-omitted fact: a 'thymulin' product that doesn't deliver the active zinc-bound form isn't delivering the thing that works.

Is there human evidence that thymulin works as a treatment?

Not really. The evidence base is old and overwhelmingly preclinical (animal and test-tube), and there are essentially no modern controlled human trials showing a real clinical benefit from injected thymulin. Its main documented human use has actually been as a blood marker of zinc status, not as a therapy.

Is 'PAT' the same as thymulin?

No. PAT (thymulin-related peptide) is a synthetic analog — a different, man-made molecule. It carries most of the more recent pain-relief and brain-inflammation findings, which should not be transferred onto native zinc-thymulin as if they were the same compound.

Is thymulin banned in sport?

It is not specifically named on the 2026 WADA Prohibited List, but that isn't a clearance — peptide hormones and immunomodulators can fall under broader categories, and this status is an inference rather than a verified ruling. Athletes must verify against the official WADA list and their anti-doping authority.

Primary sources

References

PMID 827370Bach & Dardenne, C R Acad Sci 1976 — original isolation and Edman sequencing of serum thymic factor (thymulin) from pig serum
PMID 2413455Gastinel et al., PNAS 1985 — a zinc-dependent epitope on the thymulin molecule; apo-peptide inactive
PMID 3711109J Biol Chem 1986 — NMR structure; nonapeptide, zinc-dependent immunoregulation
PMID 2657247Med Oncol Tumor Pharmacol 1989 — 'Thymulin, a zinc-dependent hormone'
PMID 3262625Prasad et al., J Clin Invest 1988 — serum thymulin in human zinc deficiency (biomarker use)
PMID 12110619Br J Pharmacol 2002 — PAT (thymulin-related peptide ANALOG) analgesic/anti-inflammatory in rat
PMID 24588820Curr Pharm Des 2014 — review: thymulin physiology and therapeutic potential
PubChem CID 71300623PubChem record — identity (CID, formula, MW, CAS)
WADA 2026WADA 2026 Prohibited List — thymulin not named; classification an inference

Research use only · Not medical advice · Updated 2026-06-01