Immune system
A zinc-dependent hormone from the thymus gland that helps immune cells mature — studied for restoring weakened immunity.
Start here
Thymulin (FTS) is a small hormone your thymus gland produces to help immune T-cells mature, and it only works when bound to zinc. It is studied for restoring immune function in aging and in zinc-deficiency-related immune weakness, and for calming inflammation. It is given by injection and is a research compound, not FDA approved, with limited human trial evidence.
Thymulin is a small hormone (nonapeptide) naturally made by your thymus gland, 78 which is like your immune system's training center. It's the boss that tells immune cells how to develop properly and when to calm down inflammation. The catch: thymulin NEEDS zinc to work. 6 Without zinc, it's like having the instruction manual but no batteries. As you age, your thymulin levels drop, 910 which is why older people get sick more often. This peptide restores thymulin activity and helps your immune system remember how to fight infections and balance inflammation.
Used for immune restoration in aging, zinc deficiency-related immunodeficiency, chronic infection, and cancer treatment side effects; works synergistically with zinc supplementation.
Thymulin (Zn-FTS) is a peptide of nine amino acids (pGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn). It is released by reticulo-epithelial (surface-lining tissue) cells of the thymus (an immune gland in the chest) and works as a thymic hormone that T lymphocytes (a type of white blood cell) need to develop and mature. 58 The zinc cofactor (Zn2+, a zinc ion the peptide needs) is built into thymulin's active site and is essential for its 3D shape and for binding to its receptors (docking points on cells). 68 How it works: (1) T cell maturation: Thymulin helps immature thymocytes (young immune cells) turn into mature T cells by signaling through specific receptors on the cell surface. It increases both CD4+ helper T cells and CD8+ suppressor/cytotoxic T cells (which hold back or kill harmful cells); 7 (2) Anti-inflammatory signaling: Thymulin blocks activation of NF-κB (a master switch for inflammation), lowers production of the inflammation signals IL-6, TNF-α, and IL-8, and reduces phosphorylation of p38 MAPK (the chemical tagging that switches on an inflammation-related enzyme); 141516 (3) Immune balance: Thymulin keeps helper and suppressor T cells in proper balance; 712 when this balance is lost, it contributes to immunodeficiency (a weak immune system) and autoimmunity (the immune system attacking the body); (4) Brain protection: Microglia (immune cells of the brain and spinal cord) respond to thymulin and reduce the brain inflammation caused by endotoxin (a bacterial toxin) by blocking NF-κB; 151718 (5) Aging: Thymulin levels fall with age (about 50% lower by age 60), which adds to immune senescence (the immune system wearing down with age). Restoring thymulin can reverse age-related thymic involution (shrinking of the thymus). 911 Zinc deficiency lowers the amount of active thymulin even when the thymus makes normal amounts, 1112 so taking zinc along with it is critical for it to work.
Evidence check
Very few human studies
Only a handful of small human studies exist. Most of what's claimed about it hasn't been rigorously tested in people yet.
Every numbered marker on this page links to one of the 25 sources at the bottom.
Immune Restoration
Thymulin directly promotes T cell differentiation and maturation, restoring healthy immune function in aged, malnourished, or immunocompromised individuals. Strong mechanistic basis in human cell research and extensive animal models.
Anti-Inflammatory
Strongly blocks NF-κB and p38 MAPK (two inflammation-driving cell pathways), which lowers body-wide inflammation and inflammatory immune signals. Effective in animal models of lung disease with no reported toxicity. How it works is well understood at the molecular level.
Age-Related Immune Decline
Thymulin levels decline with age; supplementation can reverse thymic involution and restore immune competence in elderly populations. Supported by observational studies showing thymulin correlation with immune function across lifespan.
The most-asked question
The research-reported range is 1–2 mg, once daily. Studies used different doses for different situations — find yours:
Immune support, Anti-aging
1-2 mg
Research-practice dose for immune support. Thymulin must be injected because little of it is absorbed by mouth, and it needs a zinc ion to work, so zinc is commonly taken with it 1.
Conservative start, Research use
100-400 mcg
Lower microgram-range intradermal dosing is used in some research protocols as a conservative entry point 1.
The ceiling: 500 mcg daily; exceeding this without medical supervision not recommended
Reconstitution, in plain words
Peptides usually arrive as a freeze-dried powder in a small vial. “Reconstitution” just means adding sterile water back in so you can measure a dose. Here's how it works for Thymulin (FTS):
If vial contains 1 mg (1000 mcg) thymulin: To achieve 250 mcg per injection, reconstitute with 4 mL bacteriostatic water, then draw 1 mL for 250 mcg dose.
Total mcg in vial ÷ Total mL reconstituted = mcg per mL. Then (Desired dose in mcg ÷ mcg per mL) = mL to draw.
Three quick questions — your vial, your water, your dose — and it tells you the exact syringe mark. “Find dose amount” is preloaded with Thymulin (FTS)'s recorded schedule.
Injection sites & technique
Injection under the skin
Timing
Evening, preferably 6-8 PM to align with natural thymic hormone rhythm 20
Zinc supplementation should be taken with food if possible to improve absorption and reduce stomach irritation
Separate thymulin injection from zinc supplement by at least 2 hours if supplementing with separate zinc dose. Can combine in reconstitution if using zinc-supplemented formulation.
The honest list
These show up most often. They usually fade as your body adjusts.
Mild redness, swelling, or itching at injection site lasting 1-2 hours post-injection
What to do Rotate injection sites daily, apply ice if swelling persists, use smaller gauge needle (31G recommended)
Temporary fatigue during first 1-2 weeks as immune system begins mobilization; may feel 'immune activation response'
What to do Ensure adequate sleep (8+ hours), stay hydrated, continue standard activity unless severe, usually resolves by week 2-3
Mild to moderate headache, usually occurring within hours of injection, lasting 2-8 hours
What to do Take acetaminophen or ibuprofen if needed, ensure hydration, rest in quiet environment, may decrease with subsequent doses
Worth knowing about, but most people never see these.
Low-grade fever (99-100.5°F) or transient chills representing immune system activation
What to do Monitor temperature, use acetaminophen if needed, ensure hydration, notify provider if persists beyond 24 hours or exceeds 101°F
Increased dream intensity or occasional insomnia linked to immune activation during sleep-dependent immune consolidation
What to do Inject in morning instead of evening if disruption severe, maintain consistent sleep schedule, avoid stimulants before bed
Temporary loss of appetite or unusual taste sensations during adaptation phase
What to do Eat smaller, frequent meals, focus on nutrient-dense foods, monitor weight, should resolve within 1-2 weeks
Mild enlargement of cervical or axillary lymph nodes from immune activation, not pathological
What to do Monitor size and symptoms, usually resolves within 1-2 weeks, contact provider if accompanied by fever or persists beyond 3 weeks
Rare, but if any of these happen, stop and contact a medical professional.
Rare but possible anaphylaxis or severe hypersensitivity response to peptide or reconstitution components
What to do Stop use immediately, seek emergency medical care, keep epinephrine auto-injector available, inform provider of peptide use
Too much release of inflammatory immune signals (cytokines (immune signaling molecules)) in susceptible people, which could in theory resemble a cytokine storm (a dangerous, out-of-control immune reaction). This is a theoretical risk.
What to do Lower the dose right away, talk to your doctor, consider stopping for a while, and have blood markers of inflammation checked.
Week by week
Is it right for you?
This information is for research purposes only. Stopping thymulin or any peptide should be discussed with a qualified healthcare provider. Do not discontinue abruptly without medical guidance. If experiencing emergency symptoms, seek immediate medical attention.
Thymulin levels naturally drop significantly in elderly populations. 910 Supplementation can restore T cell maturation and immune responsiveness in aging. 23 Research shows thymulin can reverse age-related thymic involution and restore helper/suppressor T cell balance. 711
In severely malnourished individuals, the thymus shrinks and T cell development is impaired. 24 In vitro (in lab dishes, not living bodies) studies show thymulin can restore T cell maturation even in those with thymic involution, 13 making it useful in recovery protocols.
Thymulin blocks NF-κB (a master switch for inflammation) and lowers inflammatory immune signals (IL-6, TNF-α, IL-8) 1416. Animal studies show it works in lung diseases, inflammatory pain, and inflammation in the brain and nerves 141517. Its anti-inflammatory effect works by suppressing p38 MAPK (an inflammation-driving cell pathway) 15.
Thymulin is a naturally occurring thymic hormone with favorable safety profile in research. No reported serious adverse events in animal models even at high doses. 814 Limited human safety data but observed studies suggest good tolerability. Requires concurrent zinc supplementation for biological activity 67 and additional safety assurance. Most concerns relate to immune overactivation in susceptible individuals, not direct peptide toxicity.
Safety data derives primarily from animal models and in vitro (in lab dishes, not living bodies) human studies. Direct human clinical trials are limited. 21 Long-term safety profile in healthy volunteers not extensively documented. Use should be considered research-level, not FDA-approved therapeutic.
Keeping it good
Store lyophilized powder at 2-8°C (preferred) or 18-25°C in original sealed vial, protected from light and moisture. Do not freeze.
Store reconstituted solution at 2-8°C in sterile vial or syringe. Keep sealed to prevent contamination. Use within 5-7 days.
Not our opinion — the published record
2014
This study investigated the properties and effects of Thymulin (FTS), contributing to our understanding of its mechanism of action and potential therapeutic applications.
Bach JF, et al.
2010
A review of two decades of clinical and experimental work on the anti-inflammatory potential of three thymic hormones (hormones from the thymus, an immune gland): thymulin, thymosin alpha and thymopoietin. It covers their role in the systemic inflammatory response (body-wide inflammation) and inflammatory diseases, and proposes effects on immune cells in the blood and two-way coupling with the hypothalamic-pituitary-adrenal axis (the brain-to-adrenal-gland stress hormone system).
Lunin SM, Novoselova EG
1989
This study investigated the properties and effects of Thymulin (FTS), contributing to our understanding of its mechanism of action and potential therapeutic applications.
Bach JF, Dardenne M
1992
This study investigated the properties and effects of Thymulin (FTS), contributing to our understanding of its mechanism of action and potential therapeutic applications.
Safieh-Garabedian B, Kendall MD, Khamashta MA, et al.
1977
The first biochemical characterisation of serum thymic factor (FTS) isolated from pig serum, showing it is a small thymus-derived peptide hormone that acts on T lymphocytes (a type of white blood cell).
Bach JF, Dardenne M, Pleau JM, Rosa J
1981
FTS loses its biological activity after passing through a chelating agent (a chemical that traps metal ions) and gets it back when zinc is added; activation follows zinc binding to the peptide. Two forms exist: one zinc-free and biologically inactive, one zinc-bound and biologically active, for which the name thymulin was proposed.
Dardenne M, Pleau JM, Lefrancier P, Bach JF
1989
Thymulin is a nonapeptide hormone (a hormone made of nine amino acids) produced by epithelial cells of the thymus, whose biological activity and antigenicity (ability to be recognized by antibodies) depend on zinc in the molecule. It makes T cells mature and boosts several functions of the various T-cell subsets (subtypes), most notably the effect on suppressor T cells (cells that hold the immune response back). The peptide is not toxic.
Bach JF, Dardenne M
2009
Review. Thymulin is produced only by epithelial cells of the thymus and consists of a nonapeptide (nine amino acids) bound to the mineral zinc in a 1:1 ratio, which gives it biological activity and a specific shape. It is involved in T cell maturation both inside and outside the thymus, has anti-inflammatory and pain-relieving properties in the brain, and has no known toxic effects even at high doses.
Reggiani PC, Morel GR, Console GM, Barbeito CG, Rodriguez SS, Brown OA, Bellini MJ, Pleau JM, Dardenne M, Goya RG
1978
Circulating thymic hormone activity in humans was highest at 15-30 years of age and declined after that, becoming negligible after the sixth decade (after about age 60); the age-related decline generally tracked the progressive thymic involution (shrinking of the thymus).
Lewis VM, Twomey JJ, Bealmear P, Goldstein G, Good RA
If this isn't the right fit
Your questions
Zinc is not optional—it's structurally part of thymulin's active form (Zn-FTS). Without adequate zinc, thymulin cannot bind to its receptors or exert any biological effect. 67 This is why the research designation is 'Zn-FTS' (zinc-FTS). If you're deficient in zinc, thymulin supplementation alone won't work. 12 You must take 15-30 mg elemental zinc daily. Zinc deficiency is also common in aging populations and malnutrition 22—exactly the groups that might benefit from thymulin.
PAT is a synthetic analogue (a modified version of a natural molecule) of thymulin that's designed to be more stable and potentially more potent. In research, PAT showed equal or stronger analgesic and anti-inflammatory effects than native thymulin at much lower concentrations. 1819 PAT may also have better shelf-life and stability. However, PAT has less clinical evidence than thymulin itself. If you can access PAT-based formulations, they may be preferable, but thymulin remains the most researched form.
The best measure is immune function testing: CD4+ T cell count (a key type of immune cell), CD4+/CD8+ ratio (the balance between two kinds of immune cells), and inflammatory signal levels (IL-6, TNF-α). These should improve by week 4-6. In daily life, you should notice fewer infections, faster recovery from illness, better vaccine responses, and more energy. If you cannot get immune testing, track how often you get infections, how quickly wounds heal, and your energy levels over 6 weeks.
Theoretically, yes—excessive immune activation could trigger or worsen autoimmune disease in susceptible individuals. This is why thymulin use requires caution in people with existing autoimmune conditions and why medical supervision is recommended. In research, no severe autoimmune reactions have been documented, but the risk exists. Start low, dose slowly, monitor closely, and stop if you notice signs of autoimmune flare (new rashes, persistent inflammation, joint pain).
Most research protocols use 4-6 week cycles. You could potentially cycle thymulin (e.g., 6 weeks on, 2-4 weeks off) to avoid tolerance or give your immune system recovery time. However, optimal cycling schedules haven't been formally studied. Some people use thymulin as a short-term immune restoration tool (one 4-6 week cycle) during aging or recovery from malnutrition. Consult with a healthcare provider about your specific situation.
No. Thymulin is a research compound without FDA approval in the United States. 25 It exists in a gray zone: there are no direct clinical trials of native thymulin on ClinicalTrials.gov, 21 only observational studies and extensive animal research. This means efficacy claims are based on preclinical (animal or lab studies, not human trials) data and in vitro (in lab dishes, not living bodies) human studies, not large-scale human trials. Use should be considered experimental and research-level.
Not without medical supervision. Thymulin is an immune activator, and immunosuppressive medications are designed to suppress the immune system. They work in opposite directions. If you're on immunosuppressants (for autoimmune disease, organ transplant, etc.), talk to your doctor before using thymulin. In some cases, low-dose thymulin under medical supervision might be possible, but it requires careful monitoring.
There's no withdrawal effect or rebound, but you'll lose the immune-boosting benefits over time. Thymulin has a short half-life (2 hours), so it clears quickly. If you were benefiting from immune restoration, stopping means those benefits fade. Whether to stop or cycle depends on your goals and immune status. Consult your healthcare provider before stopping.
Possibly, but this combination hasn't been well-studied. BPC-157 has complementary anti-inflammatory effects, so theoretically combining them makes sense. Thymosin Alpha 1 has similar immune-boosting properties, so combining might cause 'overdose' effects. If you're interested in combining peptides, do so under medical supervision and start with lower doses of each to assess tolerance and monitor immune markers closely.
25 sources
Every numbered marker on this page points to one of these. Same sources, same numbering as the Thymulin (FTS) research profile on Peptide Initiative.
Want the deep science?
Every claim on this page traces back to the research database behind Peptide Initiative — studies, citations, clinical trial data, and the technical detail we deliberately left out here.
Open the research profileThis guide is education, not medical advice. Thymulin (FTS) is a research compound that is not FDA-approved for human use. Talk to a clinician before taking anything.
PeptideGeek