Some human trialsNot FDA approved

Thymosin Alpha-1 side effects

Also known as: Ta1 · TA-1 · Thymalfasin · Zadaxin · Thymosin alpha 1

Updated Oct 24, 202626 sources

8 side effects reported for Thymosin Alpha-1: 3 from studies and labels, 5 from users and guides. 2 come with the ways people manage them.

Thymosin Alpha-1 overview

Side effects reported in studies and labels

Rates as each trial or label states them. A rate from one trial does not carry over to research-grade vials or other doses.

From trials and regulators3

Clinical studies and regulatory documents.

Local discomfort at the injection site
The main reported effect on the label; infrequent and mild
Redness, transient muscle wasting at the site, joint aches with hand swelling, rash
Rare, per the label
Adverse events overall, sepsis trial
66.4% on thymosin alpha-1 vs 67.6% on placebo; serious events 26.8% vs 29.3%

Side effects users and guides report

What people post and what dosing guides list. These are reports, not measured rates.

From users and guides5

Community reports, competitor and vendor guides, media.

Temporary liver enzyme (ALT) rise during hepatitis treatment
Common in hepatitis B and C use; transient rise above 2 times baseline
How people manage it
- Liver tests every 3 months during hepatitis protocols
Fatigue, malaise or flu-like feeling
Common in the first few days; flu-like symptoms usually pass within 48 hours
Low-grade fever, muscle aches, headache, temporary rash
Less common
Hypersensitivity reaction
Very rare
How people manage it
- Get emergency care for hives, lip or throat swelling, wheezing or faintness after an injection
- See a prescriber for redness or rash lasting beyond 48 hours, or joint aches with hand swelling
Injection-site reactions and passing fatigue
Occasional; some users link the fatigue to immune activation

Who should avoid it, and what not to combine

Deliberate immunosuppression, such as transplant recipientsCondition
The label calls it contraindicated in people who are being deliberately immunosuppressed, since it pushes immune activity.
Known allergy to thymosin alpha-1Condition
Contraindicated on the label.
PregnancyCondition
Label Pregnancy Category C: only if the benefit clearly outweighs the risk. Guides advise against use in pregnancy and breastfeeding.
Active autoimmune flareCondition
Extra immune stimulation could worsen an autoimmune flare; guides list it as a caution.
Biologics, systemic steroids or other immunosuppressantsSubstance
Guides say only with a prescriber's sign-off, since the drugs pull in opposite directions.
Another drug in the same syringeSubstance
Guides say never mix it with another drug in one syringe.

How much is known

Some human trials

Many human trials, mixed results. Hepatitis B: Cochrane 2026 pooled 10 RCTs (1,349 people) and rated nearly all outcomes very low certainty. Sepsis: the TESTS trial (1,106 adults) found no 28-day mortality benefit. COVID-19: one retrospective study reported lower mortality, but a 9-study meta-analysis found none. General immune support, longevity and 'when sick' use in healthy people have no trial.