Reference

Last reviewed: 28 Apr 2026
Sources cited: 9

Compound class~880 Da

Synthetic thymosin β4 fragment

Based on the LKKTETQ actin-binding core (residues 17–23 of thymosin β4). Not full Tβ4 — commercial products vary in exact sequence.

TB-500

Last verified: 2026-04-24

At a glance


Also known as	TB4 fragment, synthetic thymosin β4 peptide (commonly — and loosely — conflated with full-length thymosin β4)
Class	Synthetic peptide mimicking the active region of thymosin β4
Typical route	Subcutaneous injection, intramuscular injection
Plasma half-life	Reported variously as 2–4 days, or up to 10 days in some sources — inconsistent across literature, not definitively established in humans
Duration of effect	Long relative to most peptides; 2–3× weekly dosing is typical because of extended plasma presence
Molecular weight	~880 Da (for the 7-amino-acid active fragment)
Sequence	Based on the actin-binding core sequence LKKTETQ (positions 17–23 of thymosin β4); commercial “TB-500” products vary in exact sequence

What it is

This is the single most important thing to understand about TB-500 before reading any content about it anywhere:

TB-500 is not thymosin β4. TB-500 is a synthetic peptide designed to mimic the active region of thymosin β4 (Tβ4), primarily built around the LKKTETQ actin-binding sequence (amino acids 17–23 of the full 43-amino-acid Tβ4 molecule). It’s simpler, cheaper to manufacture, and captures most — but not all — of Tβ4’s biological activity.

Most biohacker content treats “TB-500” and “thymosin β4” as interchangeable. They’re not. The full-length Tβ4 molecule (under development as the drug RGN-259) has entered proper Phase III clinical trials for ophthalmic use; that evidence does not automatically transfer to the TB-500 fragment sold by research-chemical suppliers. This distinction matters for both efficacy expectations and safety framing.

TB-500 is used primarily for tissue repair, wound healing, tendon/ligament/muscle injury recovery, and systemic anti-inflammatory effect. It is frequently stacked with BPC-157 as the “Wolverine Stack” — BPC-157 for local tissue repair, TB-500 for systemic delivery of repair signalling.

Mechanism

Thymosin β4 (and by extension its active fragment in TB-500) has multiple documented mechanisms:

G-actin binding. The core mechanism. Tβ4 binds to G-actin (monomeric actin), sequestering it and regulating actin polymerisation. This affects cell shape, migration, and cytoskeletal dynamics — foundational to how cells move to wound sites.1
Cell migration promotion. Downstream of actin regulation: keratinocytes migrate 2–3× faster in Tβ4’s presence, accelerating wound closure.2
Angiogenesis. Tβ4 promotes formation of new blood vessels from pre-existing vasculature — critical for delivering oxygen and nutrients to healing tissue.3
Anti-inflammatory signalling. Downregulation of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), reduction of oxidative stress, modulation of NF-κB signalling.
Anti-scarring / anti-fibrotic. Reduces myofibroblast formation during wound repair, resulting in less scarring and more organised tissue architecture.
Hair follicle development. Documented promotion of hair follicle formation in animal models — an under-discussed use-case.3

Caveat on TB-500 vs Tβ4 mechanism overlap: TB-500’s LKKTETQ core captures most of the actin-binding and cell-migration activity. It captures less of the full-length Tβ4’s effects on other pathways, which depend on different regions of the molecule. So while “TB-500 works through Tβ4 mechanisms” is broadly true, the fraction of those mechanisms captured depends on which TB-500 product you’re actually using (sequence varies between suppliers).

Routes of administration

Subcutaneous injection


Bioavailability	High; standard subQ efficiency
Onset	Systemic tissue effects accumulate over days to weeks; no acute subjective effect
Duration	Long — 2–3× weekly dosing is the community standard because of extended plasma presence
Typical dose (this route)	2–5 mg per injection, 2–3× weekly loading; 2–5 mg weekly maintenance
Equipment	Insulin syringe (U-100), BAC water, alcohol wipes; larger volumes than smaller peptides
When this route makes sense	The evidence-aligned default. Most animal and community protocols use subQ.

The community default. Loading phase protocols often use higher frequency (2–3× weekly at 2.5 mg) for 4–6 weeks, followed by maintenance (1–2× weekly). The long half-life is genuinely useful — most peptides require daily or twice-daily dosing. TB-500 often fits a Monday/Thursday pattern.

Intramuscular injection


Bioavailability	Similar to subQ for peptide distribution
Onset	Same slow systemic accumulation
Typical dose (this route)	2–5 mg (same as subQ)
Equipment	Longer needle (0.5–1 inch), IM injection
When this route makes sense	Local delivery to an injured muscle group; occasional community practice

Some community users inject TB-500 IM directly into the vicinity of an injured muscle or tendon group, aiming for concentrated local effect. Evidence for meaningful localisation advantage over subQ is weak — the compound’s long half-life and systemic mechanism suggest distribution is similar either way.

Topical (RGN-259 ophthalmic only — not community TB-500)


Bioavailability	Local ocular delivery; direct corneal contact
Formulation	0.1% ophthalmic solution (RGN-259)
Dose	6 drops per eye per day in clinical trials
When this route makes sense	Pharmaceutical use only. This is not what research-chemical TB-500 users do.

The Phase 2 and Phase 3 clinical trials for dry eye disease used the full-length Tβ4 molecule formulated as 0.1% ophthalmic drops (RGN-259). This is a specific pharmaceutical preparation. Users mixing research-chemical TB-500 into eye drops are not replicating this — different molecule, different formulation, no safety or efficacy data for the ad-hoc version.

Oral / sublingual


Bioavailability	Negligible. TB-500 is a 7-residue peptide but lacks the GI-stability features of BPC-157 or KPV.
Typical dose (this route)	Not recommended
When this route makes sense	Never, practically. Some vendors sell oral TB-500 capsules; evidence for meaningful absorption is absent.

Despite being similar in size to KPV (3 amino acids) and smaller than BPC-157 (15 amino acids), TB-500 does not reliably survive GI transit. It lacks the structural features that make BPC-157 gastrically stable and does not appear to be a PepT1 substrate like KPV. Oral products exist; the evidence supporting them doesn’t.

Cross-route comparison

SubQ is the default and most evidence-aligned route for the healing and tissue-repair use-cases that drive community interest.

IM is a reasonable variant for users wanting locally-concentrated delivery to an injured muscle group, though the theoretical advantage is small given systemic distribution patterns.

Topical is a clinical pharmaceutical route using a different molecule (full Tβ4, not TB-500 fragment) in a specific ophthalmic formulation. Research-chemical TB-500 topical applications have no evidence base.

Oral doesn’t work. Don’t buy oral TB-500 capsules expecting meaningful effect.

What the evidence says

Honest summary: significant preclinical evidence for Tβ4; advanced clinical development exists but only for the ophthalmic formulation (RGN-259), not for research-chemical TB-500 injections used by biohackers.

Full-length Tβ4 clinical trials:

Phase 2 dry eye trial (2015): Small multicentre RCT, 9 patients with severe dry eye, 28-day treatment. 0.1% RGN-259 eye drops (topical Tβ4) 6× daily vs placebo. At day 56, 35.1% reduction in ocular discomfort (P=0.0141), 59.1% reduction in corneal fluorescein staining (P=0.0108). Safe and well tolerated.4 Critical: this was topical ophthalmic Tβ4, not injected TB-500 fragment.
Phase 3 neurotrophic keratopathy trial: Larger RCT, significant improvements in ocular discomfort, foreign body sensation, dryness. No significant adverse events.5 Again, topical Tβ4, not injected TB-500.

Research-chemical TB-500 specifically:

Preclinical (animal) studies are extensive. Wound healing, cardiac injury recovery, neurological injury models, hair follicle development.
No completed human clinical trials of injected TB-500 fragment at community doses for the use-cases biohackers target (tendon/ligament/muscle injury).
The commonly-quoted “61% faster wound healing” comes from animal or cell-culture studies, not human trials.
TB-500 is scheduled for FDA PCAC review on 23–24 July 2026 — one of seven peptides being considered for 503A Category 1 inclusion.6

Community evidence:

Positive reports for soft tissue injury recovery — tendon, ligament, muscle tears. Most users run TB-500 stacked with BPC-157 rather than alone.
Systemic anti-inflammatory effects reported across chronic inflammatory conditions
Hair regrowth reported anecdotally by some users — consistent with animal data but underdiscussed
“Almost nobody uses TB-500 alone” is a fair characterisation of community practice. The Wolverine Stack with BPC-157 is overwhelmingly dominant

WADA: TB-500 is banned in and out of competition for tested athletes under the S2 category (peptide hormones, growth factors).7

Typical use patterns

Observations, not recommendations.

Dose:

Loading phase: 2–5 mg per injection, 2–3× weekly for 4–6 weeks
Maintenance phase: 2–5 mg weekly
Conservative community start: 2 mg twice weekly
Higher-end protocols: 5–10 mg/week total during loading, 2–5 mg/week maintenance
Note on units: TB-500 is typically dosed in milligrams, not micrograms. A 5 mg dose is substantially larger than any BPC-157 or Semax dose.

Timing:

Flexible; no acute subjective effect to time around
Usually dosed morning or pre-bed by community convention
Injection timing relative to meals doesn’t matter (no GI involvement)

Cycle:

Typical: 4–8 weeks loading + ongoing maintenance, or 8–12 weeks full cycle then break
Injury-focused protocols: continue through visible functional recovery (often 12+ weeks for significant tendon/ligament injury)
Not recommended for indefinite continuous use without breaks — long-term safety at chronic doses is uncharacterised

Stacking:

BPC-157 + TB-500 is the canonical “Wolverine Stack” — BPC-157 daily (250–500 mcg), TB-500 twice weekly (2.5–5 mg). The combination is more common than either compound alone for injury protocols
BPC-157 + TB-500 + KPV for users with MCAS + injury — KPV pre-loads to reduce flare risk
BPC-157 + TB-500 + GHK-Cu for skin healing + systemic repair (the “Glow Stack”)
Compatible with most other peptide stacks; no documented significant interactions

For sensitive systems

TB-500 requires similar caution to BPC-157 for sensitive populations. Like BPC-157, it drives tissue repair and angiogenesis — mechanisms that can provoke initial mast cell flares in reactive individuals.

Start dose. 1–2 mg once weekly. This is significantly below standard community start of 2.5 mg twice weekly.

Ramp. Hold the start dose for 2–3 weeks. If tolerated, advance to 2 mg twice weekly. Sensitive users rarely need to reach the 5 mg loading doses.

Expected adjustment profile:

Initial flare pattern similar to BPC-157 — headache, fatigue, watery eyes, flushing, GI upset possible in the first 3–7 days. Consistent with the compound’s angiogenic/repair activity mobilising already-reactive mast cells
Slower onset than BPC-157 — because doses are weekly rather than daily, the flare build-up pattern is different and may be delayed
Long half-life means slow-to-clear reactions — if a reaction emerges, it persists longer than with daily-dosed peptides. This is a genuine disadvantage for sensitive users.
Injection site reactions possible — mild, transient, localised

What’s not normal and warrants stopping: breathing difficulty, facial swelling, severe prolonged flushing, any escalating reaction that doesn’t settle within 1–2 weeks. Remember that TB-500’s long half-life means the compound remains active for days after stopping — don’t expect immediate clearance.

What to have on hand:

Same antihistamine strategy as BPC-157 (H1 + H2, cetirizine + famotidine is common)
Consider KPV pre-loading for 7–14 days before starting TB-500
Electrolytes — angiogenic/vascular effects can compound with POTS symptoms

Why TB-500 is harder for sensitive systems than BPC-157:

Long half-life means no quick reversal. A bad reaction to BPC-157 clears in hours; a bad reaction to TB-500 may persist days.
Larger doses (mg rather than mcg) mean more material in the system
Sensitive users should treat TB-500 as a compound to consider after successfully tolerating BPC-157, not as an alternative or simultaneous start

Stop criteria. More conservative than for BPC-157. Stop if flare exceeds 1 week, is severe at any point, or includes unexpected systemic symptoms.

Interactions worth considering:

BPC-157: the “Wolverine Stack” is the main context; for sensitive users, introduce sequentially (BPC first, stabilise, then add TB-500) rather than simultaneously
KPV: complementary — KPV’s anti-inflammatory and mast cell calming effects can smooth TB-500 introduction
LDN, cromolyn, ketotifen: all compatible; no documented interactions
SSRIs/SNRIs: no documented interaction
Anticoagulants: theoretical concern — TB-500 is co-released with factor XIIIa by platelets and has effects on clotting pathways. Not a known clinical issue but worth flagging if on warfarin, DOACs, or antiplatelet therapy.
Beta-blockers for POTS: TB-500’s angiogenic/vascular effects may compound dizziness early in the protocol

PMDD note: no specific relevance documented. Not a primary PMDD consideration.

Reasonable expectations

Onset. No acute subjective effect. Tissue-level effects accumulate over 2–4 weeks minimum. Functional improvement in tendon/ligament/muscle injuries typically reported 4–8 weeks into a protocol. Hair regrowth effects, if they occur, are even slower.

Response rate. For soft-tissue injury recovery (the primary use-case), community reports suggest 60–70% of users report clear functional benefit when stacked with BPC-157. Response rates for TB-500 alone are lower — which is part of why the Wolverine Stack pattern dominates.

What the literature actually supports.

Actin regulation and cell migration (mechanism): well-established in cell biology
Topical Tβ4 for corneal/ocular healing (RGN-259): strong Phase 2 and Phase 3 human data — but this is not what injected TB-500 users are doing
Wound healing in animal models: strong and well-replicated
Tendon/ligament repair in animals: reasonable signal, not replicated in human RCTs
Hair follicle development in animals: documented, under-discussed in humans
Injected TB-500 for human soft tissue injury: no controlled human trial data. Community use is ahead of the evidence.

What not to expect.

Effects equivalent to the RGN-259 dry eye trial results. Different molecule, different formulation, different route, different indication.
Rapid visible healing. Weeks, not days. Anyone reporting dramatic change in the first week is likely reporting placebo or initial-inflammation-reduction effect, not tissue repair.
A substitute for proper physiotherapy, rehab, or surgical intervention for serious injuries.
Hair regrowth as a primary outcome. It happens in some animal and anecdotal reports; it’s not a reliable effect.
Equivalent evidence to regulated healing therapies (PRP, growth factor injections, stem cell). TB-500’s evidence base is meaningfully thinner.

Cost

Approximate as of April 2026, research-chemical market, UK-focused. Vendor-neutral.


5 mg lyophilised vial	£35–65
10 mg vial (bulk)	£60–110
Cost per 4-week loading cycle (2.5 mg × 2/week = 20 mg total)	~£150–250
Cost per month, sensitive-start (2 mg/week)	~£60–100
Cost per month, maintenance (2 mg × 2/week)	~£100–150
Cost per full Wolverine Stack (BPC + TB for 8-week injury cycle)	~£250–400

TB-500 is one of the more expensive peptides to run because doses are much larger (mg vs mcg for most others). An injury protocol is a genuine financial commitment at community doses.

Reconstitution

5 mg lyophilised TB-500:

Reconstitute in 2 mL bacteriostatic water → 2.5 mg/mL
2.5 mg dose = 1 mL = 100 IU on a U-100 insulin syringe (a full insulin syringe)
5 mg dose = 2 mL (typically split across two injections)

Alternative — larger dilution for precise dosing:

5 mg in 5 mL BAC water → 1 mg/mL
2 mg dose = 2 mL
2.5 mg dose = 2.5 mL
Allows more precise sub-3 mg doses; larger injection volumes

Open the Vial Plan calculator

Reconstituted TB-500 is stable in BAC water, refrigerated, for ~30 days. Lyophilised TB-500 is stable at room temperature for months. The compound is more fragile than BPC-157 — avoid vigorous shaking during reconstitution (swirl gently) to prevent peptide damage.

Areas of concern ⚠

The cancer/angiogenesis concern

This is the most important safety consideration and parallels the BPC-157 discussion.

The mechanism:

TB-500 (and Tβ4) promote angiogenesis — the formation of new blood vessels
Tumours require angiogenesis to grow beyond ~1–2 mm³ and to metastasise
Any pro-angiogenic compound could theoretically accelerate growth of an existing (possibly undetected) tumour

What the evidence actually shows:

Phase 2 trial data for Tβ4 in hundreds of patients has not reported cancer-related adverse events — this is the strongest reassurance available
No direct evidence TB-500 causes or accelerates cancer in humans has been published
The concern is mechanistic and theoretical, not empirical — but mechanistic concerns in oncology are taken seriously for good reason

What this means in practice:

In users with no cancer history: the theoretical concern is small but not zero. Routine age-appropriate cancer screening before starting is sensible.
In users with active cancer or recent cancer history: treat as contraindicated. The mechanism for tumour growth acceleration is real.
In users with significant family history: serious personalised decision. Oncologist input is reasonable before starting TB-500 in that context.
Pre-screening is a standard clinical recommendation for angiogenic peptides — this is consistent with practitioner guidance, not overreaction.

Long half-life = slow-to-clear reactions

A bad reaction to TB-500 persists for days after the last dose
This is a meaningful disadvantage for sensitive users or anyone trying a new peptide cautiously
Start low, space doses, and give time to observe response

Evidence distinction: TB-500 vs thymosin β4 vs RGN-259

Biohacker content routinely conflates these three
Clinical trial evidence is for full-length Tβ4 as the RGN-259 ophthalmic formulation
Research-chemical TB-500 is a fragment peptide, different compound, no completed human RCTs at community doses and routes
“Thymosin β4 has strong clinical evidence” is true; “therefore TB-500 does” is a fallacy

Sequence variability across suppliers

“TB-500” is not a single standardised compound
Different suppliers sell peptides with different exact sequences, all marketed as TB-500
Some use only the 7-amino-acid LKKTETQ core; others use longer fragments with additional residues
Purity and sequence verification are rare — users have limited information about what they’re actually injecting
This is different from BPC-157 (standardised 15-mer) where the molecule is at least consistent across suppliers

Long-term safety is uncharacterised

Most preclinical dosing studies ran weeks to months; no long-term human safety data exists
Chronic continuous use (>6 months) is outside anything documented
Cycling with breaks is recommended partly for this reason

WADA-banned (relevant for competitive athletes)

TB-500 is prohibited in and out of competition
Detection is possible via standard WADA testing protocols
Athletes subject to testing should not use this compound regardless of other considerations

Quality and sourcing

Research-chemical TB-500 varies more than BPC-157 in quality due to sequence-variability issues
Independent purity testing is rare
Storage: lyophilised stable at room temp; reconstituted solution refrigerated, used within 30 days; avoid vigorous agitation

Populations where caution is warranted

Active or recent malignancy — treat as contraindicated
Strong family history of cancer — serious personalised decision; not appropriate for generic biohacker use
Pregnancy and breastfeeding — no human data, default contraindication
Retinopathy or other proliferative vascular conditions — theoretical concern based on angiogenic mechanism
Bleeding disorders, anticoagulant therapy — TB-500’s co-release with factor XIIIa suggests clotting-pathway involvement; not a known clinical issue but worth flagging
MCAS/sensitive systems — usable with precautions (see “For sensitive systems”)
Under 18 — no data
Competitive athletes subject to WADA testing — prohibited in and out of competition

FDA / regulatory status

Jurisdiction	Status	Last verified
US (FDA)	Scheduled for PCAC consultation 23–24 July 2026 for potential 503A Category 1 inclusion. Removed from Category 2 on 22 April 2026. Currently defaults to “unapproved new drug” pending the PCAC outcome.	2026-04-24
UK (MHRA)	Not licensed. Not a controlled substance. Sold as research chemical with “not for human consumption” labelling.	2026-04-24
EU (EMA)	Not approved. Similar posture to UK.	2026-04-24
WADA (sport)	Prohibited in and out of competition (S2 category: peptide hormones, growth factors)	2026-04-24
Related drug (RGN-259)	Ophthalmic formulation of full Tβ4 in late-stage clinical trials; not approved	2026-04-24

Narrative. TB-500’s regulatory story is similar to BPC-157’s and KPV’s — the April 2026 Category 2 removal puts it in regulatory limbo pending the July 2026 PCAC meeting. The PCAC committee will formally evaluate whether TB-500 (free base and acetate forms) should be added to the 503A Category 1 Bulks List. A positive outcome opens legal compounding through licensed US pharmacies. The full-length Tβ4 molecule as RGN-259 is pursuing a separate, more formal pharmaceutical pathway via ophthalmic-only indications.

For UK readers: TB-500 is legally available as a research chemical from UK-based suppliers. Not a controlled substance. Personal possession is not an offence. Sale for human consumption is not permitted. WADA testing applies to anyone in a tested sport regardless of research-chemical status.

What to track in Peptrax

TB-500 is a slow-acting compound used over weeks to months for systemic recovery, and the most common honest-conversation problem is that users can’t tell at week 3 whether anything is working. The signal worth capturing is the specific recovery target — a tendon, a chronic strain, post-surgical healing, training-load tolerance — rated on the same scale weekly, with a clear baseline. Cycle length matters: 4–6 week loading phases at the higher end and longer maintenance phases at lower doses produce different curves, and logging which phase you’re in lets the retrospective make sense.

Cost-vs-effect is sharper for TB-500 than for shorter-protocol peptides because mg-range dosing on a multi-week cycle adds up fast. A typical loading cycle is real money, and the question worth answering at the end is whether the recovery target measurably moved or whether the cycle effectively did nothing at that dose. Vial use, reconstitution date, and total spend per cycle make that visible.

For users stacking TB-500 with BPC-157 (the common pairing), the attribution problem is real — both are claimed for tendon and recovery work, and without separating which compound was active when, you cannot tell which one is doing anything. Logging the stack as a first-class field, not a note, lets a later reflection actually answer the question.

For personal tracking and informational purposes only — not medical advice.