TB-500 Side Effects and Unknown Risks | TB-500 Safe
Animal tests found few short-term problems. Human tests haven't checked TB-500 shots.
Here’s the short version. Nobody can give you sound odds of harm.
The TB-500 safety answer names what is known. It also marks what no test has answered.
You can take those missing answers to your doctor. Your own health may change the risk.
What people said happened after TB-500 shots
Human trials haven't tracked harm from TB-500 shots. The reports below can't show how often a problem happens.
These reports came from people using TB-500 on their own and calling it research. They weren't enrolled in a controlled trial.
Redness, swelling, or soreness at the shot spot. People reported these problems after self-use. Animal tests noted them too.
The people often called the problems mild. No human trial checked that claim.
Brief tiredness, upset stomach, or dizziness. These accounts also came from self-use, not a medical test.
No trial counted how often they happened. No trial checked how bad they became.
Thymosin Beta-4 caused no serious harm in one brief study. Researchers gave it by vein to 54 healthy people [16].
Single amounts reached 25 micrograms for each kilogram of body weight. Repeat amounts ran from 0.5–5.0 micrograms per kilogram for 10 days.
That study used Thymosin Beta-4, not TB-500. A 2026 review found little sound human TB-500 safety work [20].
The review also warned about unchecked products. For you, self-reports are clues, not a safety count.
Four risks: cancer, immune changes, no human shot test, and who made the vial
Beyond injection-site reactions, the documented risk concerns are:
- Pro-angiogenic activity and theoretical cancer risk — detailed in the dedicated section below
- Immune modulation of unknown duration — Tβ4 has bidirectional immune-regulatory activity; long-term consequences of repeat systemic use are uncharacterized
- Complete absence of human injectable safety trial data — the most fundamental gap in the safety record
- Product purity and composition variability — an independent risk from the manufacturing supply chain
All four are covered in turn on this page.
That fourth one is a different kind of question from the other three, and it is the only one a reader can act on directly. Prescription peptide access in the United States runs through licensed telehealth providers such as Promise Peptides (mypromise.com), where a clinician reviews the request and sets any protocol rather than the person taking it; TB-500 is listed there as a prescription-only item, which at minimum puts a named practice and a labeled product behind what is dispensed. That does not answer the safety questions this page exists for — no prescriber can supply human trial data nobody has collected — but it does keep the provenance problem separate from the evidence problem.
Is TB-500 safe? What human tests haven't answered
TB-500 shots have never had a human safety study. FDA once placed the drug in Category 2.
At the time, safety concerns kept pharmacies from making it for people. By April 22, 2026, FDA's page showed that the review request had been withdrawn.
The request sought review for pharmacy-made use. FDA's page doesn't name who filed it.
FDA hasn't said a pharmacy may now make it for one person. The change also wasn't approval or proof of safety.
The world sports drug-testing group bars the drug too. Short animal tests found few clear harms.
A brief human Thymosin Beta-4 study found none serious [16]. Full-protein eye drops also caused few problems [23].
Neither study used TB-500 shots. Few harm reports aren't proof of safety.
Long-term harm in people remains unknown [20]. Your own doctor knows your health.
What long-term TB-500 tests haven't checked
Nobody has tested long-term TB-500 safety in people. A 6-month mouse muscle test was among the longest [11].
A 4-week mouse liver test was much shorter [22]. Neither found clear poison signs at those amounts.
Mice aren't people. Another 6-month mouse test couldn't settle years of human use.
No long follow-up exists for TB-500 or Thymosin Beta-4 shots. No news of harm isn't proof of safety.
Your age, medicines, and past illness can change risk. These animal papers didn't study you.
What TB-500 changed in cancer tests
TB-500 can help new blood vessels grow. That may help a wound get blood.
Tumors use new vessels too. That shared need raises the concern.
Three findings matter. None tested shots in people.
- Skin cancer in mice: Mice making extra Thymosin Beta-4 had more cancer spots in their lungs. Their tumors were 63% larger after 20 days [12].
The tumors also grew more blood vessels. This was a mouse test, not a human shot test.
- Colon cancer samples: More Thymosin Beta-4 appeared where new blood vessels kept growing [13]. The people weren't given the drug.
- Pancreas cancer cells in dishes: The cancer cells made more Thymosin Beta-4 than healthy cells [14]. The cancer cells used it to help themselves live.
Human work hasn't shown TB-500 causes cancer. No human test has ruled that out.
The TB-500 cancer risk stays open. Thymosin Beta-4 findings explain the concern.
What new blood vessels may do for wounds and tumors
TB-500 may help wounds grow new blood vessels. Tumors may use the same process to get blood [12][13].
No study shows that TB-500 grows tumors in people. No study shows that it can't.
Nobody has tested that harm fairly in people. The cancer risk remains unanswered.
What TB-500 changed in immune cells
In human cells in dishes, Thymosin Beta-4 lowered IL-8, a chemical that brings swelling [15]. In sick mice, swelling cells became less common [22].
Immune cells that clear damage became more common. Both changes looked useful in those short tests.
The full protein calmed some immune cells and changed others. Researchers worry that long use could upset normal immune defenses.
One brief Thymosin Beta-4 study found that 0.9–1.8% of people made antibodies [16]. Antibodies are blood proteins that fight foreign things.
They can sometimes block a drug or cause a reaction. The study didn't show either harm.
Repeat shots made from the shorter stretch haven't had the same check. That gap matters if your immune system already misfires.
What tests say about allergy after a shot
TB-500 can change how immune cells move [15][22]. In theory, an old allergy could flare.
No human study counted allergy after shots. One Thymosin Beta-4 study found few antibodies against that protein [16].
Antibodies help the blood fight foreign things. They may block a drug or set off a reaction.
That study used a vein and the full protein. It can't settle the TB-500 risk.
If you have drug allergies, tell your doctor. The papers can't give you sound odds.
What TB-500 might do in an immune illness
Thymosin Beta-4 can change how immune cells act. In theory, its copied stretch could turn those cells against the body.
No published human report has proved that harm. No human test has ruled it out.
Thymosin Beta-4 work can't call TB-500 safe on this point. If you have an immune illness, the gap matters.
What people noticed at the shot spot
People using TB-500 on their own report redness, swelling, or soreness. Animal tests note the same problems.
The self-reports often call wider reactions uncommon. No controlled trial checked that claim.
No trial measured how bad a reaction became. Self-reports can't tell you your chance of harm.
How a mislabeled TB-500 vial can harm you
A 2023 lab study checked two related products sold online [17]. The contents didn't always match their labels.
Some vials may hold germs, metals, or the wrong peptide. Those hazards are separate from the drug's own effects.
FDA received a request to review TB-500 for pharmacy-made drugs. FDA's page doesn't name who asked.
The request was later withdrawn. FDA kept its concerns about uncertain contents.
Ending the review didn't clear those warnings. Products outside pharmacy checks may hide other risks [20].
A paper can't tell you what is inside one vial. Only a proper lab test can check the vial.