Thymulin
Thymulin (facteur thymique serique, FTS) is a zinc-dependent 9-amino-acid thymic hormone studied for T-cell maturation and immune modulation; research protocols typically use 100 mcg subcutaneously 3x/week (dosed in MICROGRAMS, titrating within a 100-400 mcg range), with adequate zinc required for biological activity.
Research interest centers on immune modulation and T-lymphocyte maturation — supporting the differentiation of CD4+/CD8+ T-cells, balancing cytokine signaling, and studying age-related thymic decline (circulating thymulin drops roughly 90% between ages 20 and 60). It is explored as a research analog of natural thymic-hormone activity rather than as an approved therapy.
Thymulin is a nonapeptide secreted by thymic epithelial cells whose biological activity depends entirely on coordinating a zinc ion — the zinc-thymulin complex is the active form, and without adequate zinc it has essentially no immunological activity. In its zinc-bound form it binds high-affinity receptors on T-lymphocyte precursors and promotes their differentiation into functional CD4+ and CD8+ T-cells, inducing T-cell surface/differentiation markers, enhancing helper and cytotoxic T-cell function, upregulating IL-2 receptor expression, and helping balance pro- and anti-inflammatory cytokine signaling.
Most documented research protocols use 100 mcg subcutaneously about 3 times per week, titrating within a 100-400 mcg range, in defined courses of roughly 4-6 weeks. IMPORTANT: thymulin is dosed in MICROGRAMS (mcg), not milligrams — a mg dose would be ~1000x an intended microgram dose and is a serious dosing error. Reconstitute a 5 mg vial with 2.5 mL bacteriostatic water (2 mg/mL = 2000 mcg/mL) so 100 mcg = 0.05 mL = 5 units on a 100-unit insulin syringe; 400 mcg = 0.2 mL = 20 units. Because zinc coordination is required for activity, protocols commonly pair it with 15-25 mg/day of dietary or supplemental zinc. Start at the low end (100 mcg) to assess tolerance.
Not well characterized in humans; as a short-lived circulating peptide its immunomodulatory effects are studied over repeated dosing across a multi-week course rather than as an acute single-dose response.
Zinc is effectively a required cofactor rather than an optional pairing — 15-25 mg/day is commonly used to ensure biological activity. In broader thymic/immune research contexts it is discussed alongside other thymic peptides such as thymalin and thymosin alpha-1, though combined-use human data are limited.
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This page is educational reference material about compounds studied in research settings. It is not medical advice, and nothing here is a recommendation to buy, possess, or use any compound. Research findings described are from published literature; individual compounds may not be approved for human use. Talk to a licensed clinician about anything that affects your health.