Where to Buy TB-500 for Research

Thymosin Beta-4 — sold in research catalogues as TB-500 — is one of the most frequently mis-sold peptides on the market. This guide covers what the molecule actually is, what a legitimate certificate of analysis has to show, and how to tell a credible research supplier from a repackager.

Proxiva Compliance DeskResearch-use standards and labelling

What Thymosin Beta-4 actually is

Thymosin Beta-4 is a 43-amino-acid protein found in most mammalian cell types, first isolated from thymus tissue. Its best-characterised biochemical role is sequestering G-actin, the monomeric form of actin, which makes it a regulator of actin polymerisation inside the cell. That single mechanism is why it appears so often in cell-motility and tissue-culture literature.

The material sold in research catalogues as TB-500 is usually not the complete 43-residue protein. It is most often a shorter synthetic fragment corresponding to the actin-binding region — commonly the sequence around residues 17 to 23. The two are related and are frequently discussed as if identical, but they are different molecules with different molecular weights, and a mass-spectrometry result will distinguish them immediately.

This matters commercially, because vendors price the fragment and the full-length protein very differently while often using the two names interchangeably in listings. If a supplier cannot tell you which one you are buying, that is itself the answer. Proxiva lists this material as TB-500, and it is also available combined with BPC-157 in the BPC-157 and TB-500 blend for researchers running both compounds in parallel.

What the two tests each answer

Two measurements. They answer different questions and a certificate needs both.

The consequence of running only the first: a vial can report 99% and contain something else entirely, because the sample genuinely is clean — clean of a different compound. That is how a short synthetic fragment gets sold as full-length protein without a false statement appearing anywhere on the paperwork.

Purity bands

And a caveat that changes how the top row reads: HPLC purity is a proportion of UV-absorbing organic material. Net peptide by mass is always below the headline number.

One qualifier that changes how the top row reads: HPLC purity is a proportion of UV-absorbing organic material. Water, salts and counterions do not absorb. Net peptide by mass always sits below the headline number.

Reject list

Any one of these is grounds to stop. Several together describe a supplier that has not done the work.

• Lot number absent — or present but not matching the vial. Nothing else on the document applies.
• Same certificate every order. Undated, unchanging, served to everyone. Decorative.
• Figure without a trace. The chromatogram is the evidence; the percentage is a summary of it.
• No mass result. Purity cannot tell you which molecule is in the vial.
• Lab unnamed. Anonymous testing is not testing.
• No solvent panel. Synthesis leaves TFA, acetonitrile and DMF behind. Silence on them is an incomplete document, not a tidy one.
• Certificate only on request, grudgingly. Confidence publishes.

One qualifier on the fifth item: in-house testing is not automatically worthless. It carries an obvious incentive problem, so weight it lower — do not discard it outright.

Comparing suppliers on price

Headline vial prices are close to useless for comparison because fill weights differ. A $75 vial at 10mg and a $60 vial at 5mg are not what they appear to be — the second is 60% more expensive per milligram.

Convert everything to price per milligram before comparing anything. Applied across a catalogue, this reorders vendor rankings substantially. For context, Proxiva's current listings include TB-500 at 10mg, BPC-157 at 5mg, Ipamorelin, Semax 10mg and Selank 10mg. Blends such as CJC-1295 no-DAC with Ipamorelin and the KLOW 80mg blend price differently again, because the milligram figure covers several compounds at once.

Shipping origin and transit time belong in the comparison too. Peptides degrade with heat exposure, and a cheaper vial that spends two weeks in transit through a hot climate is not the better purchase.

Storage, handling and shelf life

Lyophilised peptide powder is remarkably stable. Kept cold, dry and out of light, sealed vials remain usable for long periods — the freeze-dried state removes the water that drives most degradation pathways.

Reconstitution changes that completely. Once the powder is dissolved, hydrolysis and oxidation begin, and the practical window shrinks from months to weeks under refrigeration. This is why bacteriostatic water rather than sterile water is the standard diluent for multi-draw work: the benzyl alcohol content suppresses microbial growth across repeated punctures of the stopper.

• Sealed lyophilised vials — cold storage, protected from light, stable long-term
• Reconstituted solution — refrigerated, used within a short window, never re-frozen
• Avoid repeated freeze-thaw cycles; each one costs measurable peptide integrity
• Add diluent slowly against the vial wall rather than directly onto the powder cake

Full procedure is covered separately in our guide to reconstituting research peptides.

Market conditions, 2026

Three facts, all from the past year.

• A long-established vendor ceased trading in March.
• Another was raided by the FDA.
• A third's founders were charged federally over mislabelled product.

Each had years of operating history and broadly positive community standing until the day they did not.

Consequence: vendor longevity is now a weak signal. Reputation describes the past and updates only after a failure becomes public. Verification has to happen per batch, on the paperwork, every time.

That shifts weight onto what can be checked directly — independent lab named, batch number matching, chromatogram present, solvent panel included, certificates published rather than extracted on request.

What to ask a supplier before the first order

Most sourcing problems are avoidable with four questions, and the answers are informative even when they are evasive.

"Is this the full 43-residue protein or the fragment?" A supplier who cannot answer this precisely is not handling the distinction, which means their labelling cannot be relied on. The correct answer names one or the other and points at the mass-spectrometry result.

"Can I see the COA for the batch I would receive?" Not a certificate, the certificate. If only a generic document exists, batch traceability does not exist either.

"Which laboratory performed the testing, and are they independent of the synthesis?" An in-house result is not worthless, but it carries an obvious incentive problem that an independent lab does not.

"What is the fill weight, and is the stated purity before or after accounting for water and counterion content?" This distinguishes suppliers who understand their own documentation from those reselling someone else's.

None of these are unreasonable requests, and a supplier accustomed to research customers will answer them without friction. Reluctance is data.

Frequently asked questions

Research use only. All products referenced on this page are sold strictly for laboratory and research purposes. They are not drugs, foods, cosmetics, or medical devices, and they are not intended to diagnose, treat, cure, or prevent any disease. They are not for human or veterinary consumption. Handling should be performed only by qualified individuals in an appropriate laboratory setting.