Animal data onlyNot FDA approved

TB-500 side effects

Also known as: TB500 · TB 500 · Thymosin beta-4 fragment · Ac-LKKTETQ · TB-500 acetate

Updated Oct 23, 202640 sources

9 side effects reported for TB-500: 0 from studies and labels, 9 from users and guides. 6 come with the ways people manage them.

Healing & recovery

TB-500 overview

Side effects users and guides report

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

From users and guides9

Community reports, competitor and vendor guides, media.

Headache
The most-logged side effect in one app's user data (70 logs)
How people manage it
- Hydrate
- Cut the loading dose, for example from 2 mg to 1.5 mg
Fatigue or lethargy
65 app logs; guides say it shows up 1 to 2 days after injections during loading
How people manage it
- Inject in the evening to sleep through it
Injection-site redness, sting or bruise
Called common by guides
How people manage it
- Rotate sites
- Large volumes of 0.5 to 1 mL can be split across two sites
Head rush or light-headedness
Rare
How people manage it
- Inject slowly
- Sit down for the injection
Flu-like feeling
Rare; 24 to 48 hours after the first loading dose
Nausea
Rare, mostly at 6 mg a week or more
How people manage it
- Eat a light meal first
- Split the dose
Old-injury flare or joint stiffness
Less common
All-over itching for days after each injection
One user comment
Adverse events in IV trials of full-length thymosin beta-4
40 healthy volunteers at 42 to 1,260 mg IV: infrequent, mild or moderate events, no dose-limiting toxicity or serious events. Not the fragment.
How people manage it
- Stop and get care for breathing trouble, facial swelling, spreading redness with fever, chest pain, sudden severe headache or vision change

Who should avoid it, and what not to combine

Active or recent cancerCondition
Thymosin beta-4 is raised in several tumour types and tied to cancer cell migration in lab studies. No human data.
PregnancyCondition
Guides list it as a reason to avoid.
Tested sportCondition
Prohibited by WADA at all times under S2.3.

How much is known

Animal data only

For the fragment, animal data only. One fragment trial is registered: NCT07487363, Phase 1/2 for cardiovascular markers in 80 people, recruiting since 2026-02. Full-length thymosin beta-4 has real trials: an IV safety study, a Phase 2 in heart attack (90 people, completed), RGN-259 eye drops for dry eye and neurotrophic keratitis, and topical gel for venous and pressure ulcers. FDA found no human exposure data for the fragment.