TB-500 Side Effects

Known side effects

The following side effects have been reported in research studies and user reports for TB-500:

• Headache — commonly reported in community use, particularly during initial loading phase. No incidence data from controlled human trials of injectable TB-500
• Fatigue and lethargy — frequently reported during the loading phase (first 2-4 weeks), typically resolving as dosing transitions to maintenance
• Mild nausea — reported by some users, generally transient and more common at higher loading doses
• Lightheadedness — occasionally reported after injection, particularly in the first few doses
• Injection site reactions — redness, swelling, or mild irritation at the injection site, typical of subcutaneous peptide administration
• Published human trials described the compound as safe and well tolerated — two Phase 2 dry eye trials with topical RGN-259 in 72+ subjects reported no treatment-related adverse events (PMID: 25826322, 26056426), though this was topical administration, not injectable
• Theoretical cancer concern from angiogenesis — TB-500 promotes new blood vessel formation, which theoretically could support tumor growth in individuals with existing malignancies. No human cases linking TB-500 to cancer have been published, but individuals with active cancers should avoid use as a precaution
• No published long-term human safety data for injectable TB-500 — the longest human exposure data comes from 28-day topical eye drop trials. Long-term effects of systemic injection are unknown
• No reproductive toxicity data — no studies have examined TB-500's effects on fertility, pregnancy, or fetal development
• Source quality risk — as a research-only compound not subject to pharmaceutical manufacturing standards, products marketed as TB-500 vary in purity, potency, and sterility. Third-party certificate of analysis recommended
• WADA-prohibited substance — athletes subject to anti-doping testing face a four-year ban for first-offense TB-500 detection. Military personnel under DoD policy are also prohibited from use
• Potential interaction with anticoagulants — Thymosin Beta-4's pro-angiogenic properties theoretically could affect coagulation processes, though no specific drug interaction studies have been published
• The 2024 metabolite discovery (PMID: 38382158) means the safety profile of the actual bioactive compound (Ac-LKKTE) has not been independently characterized beyond the parent peptide

Severity and frequency

Limited clinical data is available for TB-500. Side effect frequency and severity are based on available research and anecdotal reports. More data is needed for definitive safety profiles.

When to seek medical attention

Contact your healthcare provider immediately if you experience:

• Severe or persistent symptoms that do not improve
• Signs of an allergic reaction (rash, swelling, difficulty breathing)
• Severe abdominal pain
• Changes in vision or neurological symptoms
• Any symptom that concerns you

Risk factors

Side effect risk may be higher in certain populations. Discuss your complete medical history with your doctor, including:

• Pre-existing medical conditions
• Current medications (drug interactions)
• Pregnancy or plans to become pregnant
• History of allergic reactions to peptides or similar compounds
• Note: TB-500 is a research compound without established human safety data from FDA-approved clinical trials

Research references

• Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice — Wound Repair and Regeneration (2003) [PubMed]
• Thymosin beta4: structure, function, and biological properties supporting current and future clinical applications — Annals of the New York Academy of Sciences (2010) [PubMed]
• Thymosin beta4 and the anti-fibrotic switch — International Immunopharmacology (2023) [PubMed]
• Thymosin beta4 increases cardiac cell proliferation, cell engraftment, and the reparative potency of human induced-pluripotent stem cell-derived cardiomyocytes in a porcine model of acute myocardial infarction — Theranostics (2021) [PubMed]
• Thymosin beta4 Protects against Cardiac Damage and Subsequent Cardiac Fibrosis in Mice with Myocardial Infarction — Cardiovascular Therapeutics (2022) [PubMed]
• Thymosin Beta-4 Induces Mouse Hair Growth — PLoS One (2015) [PubMed]
• Multiple potential roles of thymosin beta4 in the growth and development of hair follicles — Journal of Cellular and Molecular Medicine (2021) [PubMed]
• Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial — Cornea (2015) [PubMed]
• Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model — Clinical Ophthalmology (2015) [PubMed]
• Thymosin beta4 Suppresses LPS-Induced Murine Lung Fibrosis by Attenuating Oxidative Injury and Alleviating Inflammation — Inflammation (2022) [PubMed]
• Neuroprotective and neurorestorative effects of thymosin beta4 treatment following experimental traumatic brain injury — Annals of the New York Academy of Sciences (2012) [PubMed]
• Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro — Journal of Chromatography B (2024) [PubMed]
• Thymosin beta4 and Actin: Binding Modes, Biological Functions and Clinical Applications — Current Protein & Peptide Science (2023) [PubMed]