Question 1

What are the side effects of TB-500?

Accepted Answer

The honest answer begins with an absence. No trial among the research behind this page has produced an adverse-event table for TB-500, so there is no list of reactions with percentages beside them. What exists instead is a set of reviews describing how thin the record is. A 2026 scoping review of six compounds sold for recovery notes that they are often perceived as low risk, despite the absence of efficacy or safety data for many emerging peptides. A 2026 sports medicine review is blunter, reporting that rigorous human safety data are scarce, and there is potential for serious harm to patients. Both sentences characterise a whole category rather than this one compound, and that is the position worth carrying away. A seller's reassurance rests on nobody having counted, which is a considerably weaker thing than it sounds.

Question 2

Is a thymosin beta-4 safety record a TB-500 safety record?

Accepted Answer

No, and this is the step most writing on TB-500 walks straight past. A 2026 sports medicine review lists the two as separate entries in one sentence, naming them Tβ4 (thymosin beta-4), and TB-500 (thymosin beta-4 fragment). The trial registry keeps them apart as well. The only registered study of the material sold under this name is entered as TB-500 (Thymosin Beta 4 17-23 Fragment), a numbered stretch of the parent molecule rather than the whole of it. A 2016 review describes that parent: thymosin beta 4 (Tβ4) is a small, abundant, naturally occurring regenerative protein that is found in body fluids and inside cells. Harm attaches to a molecule, not to a name. A trial recording what happened to patients given the whole protein describes the protein, at that amount, by that route. No study among the research behind this page gives both forms to the same animals, which is what reading one record onto the other would require.

Question 3

What harm has actually been documented in a person?

Accepted Answer

One finding, in nine people, and it belonged to the protein rather than to the fragment. Nine patients (ages 37-84) with chronic nonhealing neurotrophic corneal epithelial defects, meaning sores on the eye's surface that will not close, were treated with thymosin beta 4 (Tbeta4) sterile eye drops for 28 or 49 days. Stromal thinning was observed in one patient. The stroma is the thick middle layer of the cornea, so thinning it is a structural change rather than a passing irritation. The remainder of that report runs the other way, because reduced ocular irritation was reported by all patients soon after treatment initiation. That is the complete published human harm record for this molecule family, and it rewards reading twice. It is neither a reassurance nor an alarm. It is nine people, one corneal condition, drops rather than an injection, and seven weeks of exposure at the outside.

Question 4

Why is TB-500 described as banned?

Accepted Answer

No regulator has licensed either form of this molecule, for any use at all. That fact sits underneath most of what gets written about its status. A 2026 sports medicine review places the category inside a parallel "gray market" of unapproved compounds, operating largely outside of regulatory oversight. It lists the fragment among the peptides it covers. A 2026 scoping review lands in the same place from the clinical side, holding that peptide supplements should not currently be recommended as a replacement or adjunct for existing orthopaedic standard of care. Both are statements about licensing and about practice, rather than about an anti-doping list. No anti-doping register appears among the research behind this page. An athlete who competes under a code has to confirm the current status with their own governing body, not take it from a seller and not take it from us.

Question 5

Does thymosin beta-4 do anything to blood counts?

Accepted Answer

The question has one real anchor, and it is an old one. A 1992 review looked at biomolecules that suppress blood-cell production. It reports that a number of well-characterized cytokines have been implicated in the negative regulation of hematopoiesis. The list it gives runs acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) or thymosin-beta 4, beside ferritin, lactoferrin and tumour necrosis factor. Hematopoiesis is the making of blood cells in the marrow. Read that carefully. It is a review of signals a body already makes, rather than an experiment in which somebody was given one. Sitting on a list of natural brakes is not the same as having lowered a blood count in an animal or a person. No study among the research behind this page reports a blood panel in anyone given either form. The question stands open: a plausible mechanism, no measurement, and a reason to mark the gap rather than fill it.

Question 6

Is there a cancer question around thymosin beta-4?

Accepted Answer

There is one, and it comes from tumour biology rather than from anybody taking anything. A 2026 proteomic study compared what melanoma cells release before and after they become resistant to two cancer medicines. Thymosin beta-4 was among the proteins secreted in significantly higher amounts by resistant cells, beside clusterin, interleukin-6 and several matrix metalloproteinases. The authors read that as a statement about the ground around a tumour. Proteins secreted by resistant melanoma cells can undoubtedly influence the surrounding microenvironment in a way that promotes the formation of a pro-tumor niche, they write. What that is: an observation that certain cancer cells make more of this protein. What it is not: a measurement of what follows when somebody injects a fragment of it. Only the first of those two questions has been asked.

Question 7

What happened to the healthy animals in the brain studies?

Accepted Answer

One experiment produced the clearest flag in this animal literature, and it showed up in the group that was not ill. A 2023 study dosed middle-age APP/PS1 mice, which carry Alzheimer's mutations, along with their normal littermates. Both groups received a bacterial toxin, then thymosin β4 into a vein. In the Alzheimer's animals it prevented LPS-induced amyloid burden. In the normal ones it increased astrocytic and microglial proliferation in the hippocampus of LPS-treated WT mice. Astrocytes and microglia are the brain's support and immune cells, and their multiplying is an inflammatory response. The authors put both outcomes into one sentence. They report that Tβ4 can alleviate the adverse effects of systemic LPS in the brain by preventing exacerbation of amyloid deposition in AD mice and by inducing reactive microgliosis in aging WT mice. A compound doing one thing in sick animals and another in healthy ones is the pattern a safety reader wants flagged rather than smoothed over.

Question 8

Does it affect blood sugar or insulin?

Accepted Answer

Nothing has measured that directly. Giving the compound and then watching blood sugar is the experiment that would answer it, and no study among the research behind this page has run it. What follows is a warning about the category rather than a result for this compound. The 2026 scoping review attaches metabolic risk to the category as a whole. Documented risks include cardiovascular complications and metabolic dysfunction such as insulin resistance, it reports. The same review also notes that some peptides such as MK-677 were associated with significant risks including congestive heart failure, which attaches the sharpest harm in it to a different compound.

Question 9

Has anyone been given it outside a trial and written up?

Accepted Answer

Once, in four people, and as half of a combination. A retrospective chart review at a Florida clinic examined injections delivered into the knee joint across a single year. Of the 17 patients in the study, 16 were contacted by phone to follow up on the status of their knee pain. Four of them had received a combination of 2 peptide injections of BPC 157 and TB4. The authors state their own starting position: the use of peptides BPC157 and thymosin-beta-4 (TB4) has not been studied for this complaint. Of the patients who received both peptides, 75% showed significant improvement, but 25% had no relief of their knee pain. For a safety reader the methodology matters considerably more than the percentage. Four people, no control group, no physical examination, and a telephone conversation six months to a year afterwards. Nobody was investigating harm, so an absence of reported harm in four patients represents a gap in the observation rather than a finding about the compound.

Question 10

What is known about exposure in pregnancy?

Accepted Answer

One experiment speaks to it, and it was designed to look for benefit rather than harm. Ten mice received the same injection regimen, and only 6 of these 10 are part of this experiment because they were pregnant, so the result rests on six litters. What the investigators recorded was growth. The mothers treated with TB4 for two days precisely E14 and E17, showed a higher cranio-caudal length when compared to control newborns. Under the microscope, maternal TB4 treatment was associated with more advanced development of lungs, heart, kidney, cerebral cortex and notochord. Their conclusion is that TB4 administration during gestation may act as a powerful fetal growth promoter. A compound that alters how quickly organs develop in an unborn mouse has not thereby been shown harmless in a person. Six litters, one species and two injections, read against a human pregnancy, constitute a signal that something happens rather than a description of what.

Question 11

What is known about interactions?

Accepted Answer

Very little, and the one mechanistic handle comes from a mouse heart experiment. A 2025 study found that the cardioprotective effects of rhTB4 on cardiac function and adverse cardiac remodeling in I/R mice were abolished by ErbB2 inhibition. ErbB2 is a receptor on the surface of heart cells, and medicines that block it are in routine cancer care. That is a pharmacological interaction shown in mice: block the receptor and the protein's effect disappears. It says nothing about a person on such a medicine who also uses a fragment, because that pairing appears in no study among the research behind this page. The second handle is chemical rather than clinical. A 2007 review notes that several biological effects are attributed to thymosin beta(4), oxidized thymosin beta(4), or to ac-SDKP possibly generated from thymosin beta(4). The molecule has active breakdown products of its own, and what those interact with has not been asked.

Question 12

Is it all right to use TB-500 every day?

Accepted Answer

No course among the research behind this page ran a daily schedule in a person, so there is no human experience of daily administration to describe. Every daily sequence on record belongs to an animal, and the 2023 mouse work is the clearest of them. Thymosin β4 was administered immediately following and at 2 and 4 h after the PBS or LPS challenge, and then once daily for 6 days, which is the longest daily sequence anybody has published. The longest human exposure was not a daily injection at all. Nine patients were treated with thymosin beta 4 (Tbeta4) sterile eye drops for 28 or 49 days, which is seven weeks at the outside, applied to an eye. That is a different exposure from months of injection rather than a shorter version of the same thing, and the distance between those two is the whole of what remains unknown.

Question 13

Who was left out of the studies?

Accepted Answer

Almost everyone, and the published accounts rarely spell the exclusions out. Two registered volunteer studies took healthy adults by definition. They are filed as A Phase 1a Study of Thymosin Beta 4 in Healthy Volunteers and A Phase 1b Study of Thymosin Beta 4 in Healthy Volunteers, both marked COMPLETED. Healthy is itself an exclusion, since it removes the people most likely to be taking something else. The hospital work picked the other extreme. It was a randomized, placebo-controlled, double-blind trial involving 96 STEMI patients, that is, people admitted after a heart attack. The first dose went in within 8 h after PCI, the procedure that reopens the blocked artery. The eye series ran in nine patients (ages 37-84) whose corneal sores would not close. One registered safety study never enrolled anybody. A Phase 1 Safety Study of the Intravenous Administration of Thymosin Beta in Healthy Volunteers is filed as WITHDRAWN.

Question 14

What has the FDA recalled?

Accepted Answer

Four entries, all of them about how a pharmacy filled a vial. They run from 2018 to 2025, each a Class II recall of a compounded thymosin beta-4 injection. The 2018 record covers Thymosin Beta-4, 15 mg Injection from a Florida compounding pharmacy, giving its reason as Lack of sterility assurance. The 2020 record covers a THYMOSIN BETA - 4, 2000 MCG/ML, 5 ML vial, pulled for Lack of Assurance of Sterility: due to concerns with production processes which cannot assure sterility of products intended to be sterile. Two 2025 records from one Boca Raton firm cover Thymosin Beta-4 (TB4) for Injection, 15mg, all presentations and a combined BPC-157/Thymosin Beta-4 for Injection. What those files are not is a finding about the molecule. Sterility is a property of the room a vial was filled in, so an enforcement record is a document about production processes rather than about pharmacology.

Question 15

What risk does the supply itself carry?

Accepted Answer

The enforcement file covers compounding pharmacies, which are the documented and regulated corner of this supply. Everything outside that corner has been described rather than measured. A 2026 scoping review gives the shape of the wider literature, finding that significant heterogeneity existed in dosing and route of administration across the work it collected. Spread of that size says how unsettled the research is, and it says nothing about any particular vial. No published analysis among the research behind this page reports purity, identity or content for material sold under the TB-500 name. That absence bites harder here than for most compounds. The name itself denotes a fragment of a longer protein, and confirming which fragment is in a vial is laboratory work rather than anything a buyer can see through glass.

TB-500 side effects and safety data