# Thymosin alpha-1

Thymic immunomodulator approved abroad for hepatitis B/C; used to cut down on colds.

- Page: https://peprank.xyz/peptides/thymosin-alpha-1
- Category: Immune (Research peptide)
- Also known as: Ta1; TA-1; thymalfasin; Zadaxin
- Routes: Injection
- Sequence: SDAAVDTSSEITTKDLKEKKEVVEEAEN (N-acetyl (28 aa, thymalfasin))
- Safety tier: Strict: Caution · Balanced: Caution · Evidence only: Caution
- Risk axes (0 none to 3 severe): Seen harm 1, Mechanism 2, Data gap 1, Silent harm 1, Product 3
- Positive: 60% of 47 graded reports glowing or positive, shrunk toward the 49% all-report average by 8 reports' weight
- Rank: #1 of 61 research peptides
- Graded reports: 47 (Glowing 6, Positive 23, Mixed 5, Nothing 4, Negative 6, Bad reaction 3)
- Evidence: Approved drug — approved in ~35 countries (Zadaxin, hepatitis B/C, vaccine adjuvant); large human RCT (TESTS, 1,106 sepsis patients, BMJ 2025) found no mortality benefit and safety similar to placebo
- Access: Grey market
- Onset: Cold prevention is judged over a season. In chronic illness, a flu-like reaction or an energy lift often shows within 1-2 days of a dose. Antibody and autoimmune changes take 1-3 months.
- Lasts: cumulative; a single dose's reaction or lift lasts 1-2 days
- Cost per month: ≈ €38–40 (at 210–230 mcg/day, Semax Polska at €5.87/mg)
- Dose users report: 420–710 mcg/day (median 500 mcg, n=11), ≈ €74–130 a month at that dose
- Updated: 2026-10-30

## What users report

Two different crowds. Healthy parents, travellers and autoimmune users are almost uniformly positive: fewer or shorter colds while the household gets sick, falling thyroid antibodies or B cells, a few striking remissions (lupus/Sjögren's, lichen sclerosus). In long COVID, ME/CFS, MCAS and CIRS it splits roughly in half: some get energy back, but many get a flu-like immune flare or PEM crash within a day of the first dose, usually gone in days but occasionally lasting weeks to months, even at 100 mcg. Those who persist mostly titrate up from 100-300 mcg. Outright 'felt nothing' reports are only about 1 in 10.

**Effects:** fewer colds / shorter illnesses; faster clearing of lingering infections; lower thyroid/autoimmune antibodies (anecdotal); less long-COVID fatigue (anecdotal)

**Downsides:** injection-site soreness; transient flu-like feeling or low mood for a few days; cost

**Risks:** Theoretical: immune stimulation could flare autoimmune disease (a few anecdotal flares in ME/CFS); contraindicated with transplant immunosuppression; Generic: grey-market endotoxin (LPS) contamination; FDA flagged immunogenicity/impurity concerns for compounded Ta1

**Typical use:** 1.5-1.6 mg subQ twice weekly (matches Zadaxin label), often in courses during cold season or when exposed.

**Getting it:** Approved abroad as Zadaxin but not in the US; FDA Category 2 and left out of the Oct 2026 HHS compounding carve-out.

**Stacked with:** thymosin beta-4 / TB-500 (Doctors prescribe the pair for long COVID, and one ME/CFS user said Tβ4 calmed their Ta1 flare.); KPV (Pitched for long COVID, MCAS and CIRS: Ta1 to rebalance immunity, KPV to damp the inflammation.); SS-31 / MOTS-c (Long-COVID users follow an immune course of Ta1 with mitochondrial peptides for energy.)

## Risk profile

- **Seen harm 1/3:** In the 1,106-patient TESTS sepsis trial SAEs were 26.8% vs 29.3% on placebo, and the Zadaxin label lists no warnings. First-hand reports describe weeks-long crashes or flares in ME/CFS, CIRS and long COVID, isolated and confounded by the illnesses.
- **Mechanism 2/3:** Immune activation is its purpose (T-cell maturation and cytokine release), so a flare of autoimmune or inflammatory disease is credible, and the label bars it under deliberate immunosuppression.
- **Data gap 1/3:** Approved as Zadaxin in about 35 countries, though not the US, with a 1,106-patient phase 3 trial and decades of use in hepatitis.
- **Silent harm 1/3:** Immune flares and flu-like reactions are felt within days, though some lasted weeks.
- **Product 3/3:** Users buy grey-market injectable vials; FDA flagged immunogenicity and impurity concerns, and compounding was left out of the October 2026 carve-out.
- **Never if:** Transplant or other deliberate immunosuppression (label); Active autoimmune disease; Pregnancy (label)

## Top reports

- Glowing, immune, 2 mg three times a week: “Been on 2mg x 3 days a week for a month. Zero side effects. Just did blood. My thyroid antibodies have insanely decreased.” — [r/cfs](https://www.reddit.com/r/cfs/comments/1nl65vu/be_careful_about_thymosin_alpha1/ng8jb00/)
- Glowing, energy: “After fighting long covid for years, TA1 have given me much of my life back.” — [r/Biohacking](https://www.reddit.com/r/Biohacking/comments/1wrm1xm/tis_the_seasonwhere_people_get_sick/pcekfzo/)
- Glowing, immune: “Once I switched to that, in Aug. 2024, I felt extremely sick, had a huge herx, and then when it all wore off 6 weeks later, my PEM was gone. So it really was the gamechanger.” — [@sun_in_winter12 on X](https://x.com/sun_in_winter12/status/2049903100543050044)
- Glowing, immune: “On Thymosin Alpha I was sick just once in 6 months. I came off, back to a cycle of sickness for months. The bloodwork I cannot attest to, only the result for me was dramatic and evident.” — [@BetweenThieves7 on X](https://x.com/BetweenThieves7/status/2101884094585966989)
- Glowing, immune: “I’m still on this peptide THY-A1 and love it is absolutely changed my autoimmune system I have two auto immune diseases and I’m on no steroids and lowering dosing on my steroid sparing medication!!! It’s been close to six months” — [r/LOVE4DIYAESTHETICS](https://www.reddit.com/r/LOVE4DIYAESTHETICS/comments/1nztw7v/anyone_here_tried_thymosin_alpha_1_thya1_looking/o6car1z/)

## Cheapest in Europe

- [Europa-Peptide](https://europa-peptide.de/en/shop/thymosin-alpha-1-10mg/) (PL): Thymosin Alpha-1 10mg, €45, €4.49/mg
- [Semax Polska](https://semaxpolska.com/en/thymosin-alpha-1-5mg-woda-bakteriostatyczna-3ml/) (PL): Thymosin alpha 1, 5mg + bacteriostatic water 3ml, €29, €5.87/mg
- [Baltic Peptides](https://balticpeptides.com/product/thymosin-alpha-1/) (LT): Thymosin Alpha-1 10mg, €70, €7.00/mg
- [Modern Peptides EU](https://modernpeptides.eu/product/thymosin-alpha-1/) (DE): Thymosin Alpha 1, €70, €7.00/mg
- [Particle Peptides](https://particlepeptides.com/en/buy-peptides/118-thymosin-alpha-1-10mg-with-mannitol.html) (SK): Thymosin Alpha 1 10mg with Mannitol, €78, €7.80/mg

## Studies

- [Thymosin alpha 1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial](https://www.bmj.com/content/388/bmj-2024-082583) (rct, n=1106, 2025): No reduction in 28-day mortality versus placebo in sepsis; adverse events were similar to placebo.
- [Efficacy of thymosin alpha1 in patients with chronic hepatitis B: a randomized, controlled trial](https://pubmed.ncbi.nlm.nih.gov/9581695/) (rct, n=98, 1998): A 26-week course of 1.6 mg twice weekly cleared HBV DNA and HBeAg in 40.6% versus 9.4% of untreated controls at 18 months, with no significant side effects.
- [Augmentation of influenza antibody response in elderly men by thymosin alpha one: a double-blind placebo-controlled clinical study](https://pubmed.ncbi.nlm.nih.gov/2642497/) (rct, n=90, 1989): Given with the flu vaccine, it raised antibody responses over placebo, mostly in men 77 and older, with no toxicity.
- [Thymosin alpha 1 reduces the mortality of severe COVID-19 by restoration of lymphocytopenia and reversion of exhausted T cells](https://pubmed.ncbi.nlm.nih.gov/32442287/) (observational, n=76, 2020): In a retrospective Wuhan cohort, treated severe COVID-19 patients died less often (11% vs 30%) and recovered T-cell counts.

## Sources

- [TESTS: thymosin alpha-1 for sepsis, phase 3 RCT (BMJ 2025)](https://www.bmj.com/content/388/bmj-2024-082583)
- [FDA category 2 / withdrawn-nominations table (Ta1 risk note)](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks)
- [Regulatory explainer: PCAC voted 17-4 against listing Ta1 for compounding (Dec 2024); FDA rule due ~Feb 2027](https://www.bananapeps.com/research/fda-compounding-fight-explained)