Thymulin (FTS)
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.
TL;DRThe whole page · in 30 seconds
Thymic hormone · T-cell maturation · Immune balance · Zinc-dependent
A genuine thymic hormone — a tiny zinc-dependent nonapeptide ("FTS") the thymus makes to help T-cells mature and tune immune balance. Its standout feature: it is active only when bound to zinc, which makes zinc the single most important thing to get right.
The basics
- A real hormone the thymus secretes, not a designer peptide — a precisely defined nine-amino-acid molecule.
- Reached for to support T-cell maturation and immune balance, with one non-negotiable catch: zinc.
Why people use it
- Supports T-cell maturation — its documented job is helping T-cells develop and tuning immune responses.
- A real thymic hormone with genuine biology — not invented marketing; the molecule and its role are well-defined.
- The standout zinc story in the whole library — its activity is literally switched on by zinc, the clearest cofactor case here.
- Pairs naturally with the thymic family — it works at the maturation stage, so it slots alongside peptides that act downstream.
How to run it
- Dose: 1,000 mcg per dose
- How often: Daily within a cycle
- How: A small injection under the skin (belly or thigh fat)
- When: Any consistent time — zinc status matters far more than the hour
- Cycle: 4–8 weeks on, then a 2–4 week break
Stacks well with
- Thymosin Alpha-1 — the better-studied adaptive-immune partner; the two cover sequential T-cell stages.
- BPC-157 — adds tissue repair and systemic healing alongside the immune support.
Good to know
- Zinc-dependent — it only works bound to zinc, so adequate zinc intake is essential. This is the single most important practical point.
- Inject it subcutaneously (under the skin), not into muscle or a vein.
- Run it in cycles — a few weeks on, then a break — not continuously.
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.
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 827370PMID 2413455PMID 3262625PMID 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. The 1,000 mcg/day default is the conservative low end of a 1–5 mg/day range that traces to 1980s human trials of synthetic thymulin (nonathymulin), where 5 mg/day was the most effective dose in rheumatoid arthritis (Amor 1987, PMID 3310925). That is old evidence for a different indication — but it is real human dosing, not absent: what thymulin lacks is MODERN controlled efficacy data, not any human trial at all. Read this section as the practical framework for how thymulin would be administered, anchored to that historical range, with the full understanding that no modern validated human dosing exists.
Thymulin's human dosing comes from 1980s trials of synthetic thymulin (nonathymulin) in rheumatoid arthritis (Amor 1987), where 5 mg/day was the most effective dose — the calculator's 1,000 mcg/day is the conservative low end of that 1–5 mg/day range. There is no modern controlled efficacy data, and the only recent human literature is observational (thymulin as a zinc-status biomarker). Thymulin is not an FDA-approved drug.
Dose — anchored to a 1–5 mg/day historical range
Thymulin's dosing is not invented: it traces to 1980s human trials of synthetic thymulin (nonathymulin), giving a 1–5 mg/day range. What it lacks is modern controlled efficacy data, not human dosing altogether.
- 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:
- The 1–5 mg/day range comes from 1980s trials of synthetic thymulin (nonathymulin), where 5 mg/day was the most effective rheumatoid-arthritis dose (Amor 1987, PMID 3310925). The calculator's 1,000 mcg/day is the conservative low end of that range. This is old evidence for a different indication — treat it as a historical anchor, not a modern validated regimen.
- 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 dose to syringe units (e.g. 1,000 mcg = 20 IU with the standard 10 mg + 2 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 + 2 mL bacteriostatic water = 5,000 mcg (5 mg) per mL. On a 100-unit (1 mL) insulin syringe: 1,000 mcg = 20 IU · 2,000 mcg = 40 IU · 2,500 mcg = 50 IU · 5,000 mcg = 100 IU.
- Why 2 mL:
- This matches the on-page calculator default, so the syringe units shown above line up exactly with what the calculator returns for the 1,000 mcg dose (20 IU).
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 default 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 default 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 default 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
Reconstitution calculator
Calculated for a 1 mL U-100 insulin syringe (100 units/mL).
Units per dose
20
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
Thymulin's human dosing is old, not absent — a 1–5 mg/day range from 1980s synthetic-thymulin (nonathymulin) trials (Amor 1987); what is missing is modern controlled efficacy data. The table below is historical and largely preclinical, shown to illustrate the science, not to prescribe 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.
| 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 |
| 1–5 mg/day | Human (interventional) | Synthetic thymulin (nonathymulin) in rheumatoid arthritis (Amor 1987) | 1980s human trial of synthetic thymulin: 5 mg/day was the most effective dose in rheumatoid arthritis — the source of the 1–5 mg/day range. Old evidence, a different indication, and no modern controlled replication, but a real human dosing record | PMID 3310925 |
| 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 3310925Amor et al. 1987 — synthetic thymulin (nonathymulin) in rheumatoid arthritis; 5 mg/day most effective (source of the 1–5 mg/day range)
- 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
Reviewed by Ki Researcher Team · Research use only · Not medical advice · Updated 2026-06-19