Thymulin, a zinc-dependent hormone made by the thymus gland and sold as an unregulated research chemical, draws interest for keeping the aging immune system younger. Human evidence is thin and old: small 1980s studies found improvement in rheumatoid arthritis, not multiple sclerosis. Longevity-relevant findings come from mice and lab-grown cells. Correcting zinc deficiency is the only related approach with human data. No long-term safety data exist. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Plasma zinc | At least 70 µg/dL | Thymulin is inactive without zinc; guides zinc dosing |
| Serum copper | About 70–140 µg/dL | Detects zinc-induced copper deficiency |
| CBC with differential | Hemoglobin about 12.0–15.5 g/dL in women, 13.5–17.5 g/dL in men; white cells about 4,000–11,000/µL | Anemia or low white cells signal zinc excess or immune change |
| Prolactin | About 4–15 ng/mL in men, 4–23 ng/mL in women | Thymulin releases prolactin in rat pituitary cells |
| TSH | About 0.4–4.0 mIU/L | Thymulin releases TSH in rat pituitary cells |
| hs-CRP | No established target; track change from own baseline | Thymulin lowered inflammatory signaling in aged mice |
Cadence: Zinc, copper, CBC, prolactin, TSH and hs-CRP at baseline; zinc, copper, prolactin and TSH at 4–8 weeks, then every 3–6 months; CBC and hs-CRP every 3–6 months during continued use