Thymosin Alpha-1 vs TB-500
Same first name, nothing else in common. Which thymosin do you actually want?
Reviewed by the amino101 editorial team. , first published .
This is the most common name mix up in the peptide space. Thymosin alpha-1 and TB-500 both trace back to thymus extracts isolated in the 1970s, and that is where the similarity ends. Thymosin alpha-1 is a 28 amino acid immune peptide, sold as thymalfasin under the brand Zadaxin, that primes dendritic cells and T cells. It is an approved drug in China, Italy and more than 30 other countries for chronic hepatitis B and as a vaccine and chemotherapy adjuvant, with randomized trials behind it, though it has never been approved in the US. TB-500 is a synthetic fragment of thymosin beta-4, usually the 7 amino acid actin binding segment, that regulates how cells move into a wound. It is used for tendon, ligament and muscle recovery, has no human trial of the fragment, and is not approved anywhere. One acts on immune cells and has no tissue repair effect of its own; the other acts on tissue and has no immune indication. They are dosed differently, cycled differently and bought for different reasons. This is an educational comparison; vendors sometimes mislabel the two, so the label matters more than usual.
| Thymosin Alpha-1 | TB-500 | |
|---|---|---|
| Typical dosage | 0.5 to 1.6 mg | 2 to 5 mg |
| Frequency | twice weekly, up to daily in short acute protocols | twice weekly during loading, then weekly or every other week |
| Route | Subcutaneous | Subcutaneous, Intramuscular |
| Half-life | about 2 hours in plasma | roughly 1 to 2 hours in plasma (estimated); the full protein persists longer in tissue |
| Cycle | 4 to 12 weeks in community use; 6 months in the hepatitis B labeling | 4 to 6 week loading phase, then maintenance or stop |
| Research level | Well researched | Limited research |
| Human trials | Approved drug | Randomized trials |
| Status | Approved in more than 30 countries as Zadaxin (thymalfasin) for hepatitis B and as an immune adjuvant; not FDA approved. Treated as prohibited by WADA under S0. | Investigational, not FDA approved. Prohibited by WADA for athletes. |
| Effects timeline | nothing to feel in the first weeks; immune markers and infection frequency are judged over 2 to 6 months | flexibility and reduced stiffness 1 to 2 weeks, injury recovery 4 to 6 weeks |
Key differences
Thymosin Alpha-1 vs TB-500 dosage
Dosage patterns reported in research and community protocols, by goal. Taken from each compound page. Not a prescription.
| Goal | Dosage | Frequency |
|---|---|---|
| Approved hepatitis B schedule | 1.6 mg | twice weekly for 6 months |
| Vaccine adjuvant | 1.6 mg | twice weekly for 4 weeks starting at vaccination |
| General immune support, community | 0.5 to 1 mg | 2 to 3 times weekly |
| Acute illness, community | 1.6 mg | once daily for 5 to 7 days |
| Goal | Dosage | Frequency |
|---|---|---|
| Loading phase | 2 to 2.5 mg | twice weekly |
| Maintenance | 2 mg | every 1 to 2 weeks |
| Acute injury, higher end | 5 mg | twice weekly for 2 to 4 weeks |
| Flexibility and general recovery | 2 mg | once weekly |
Convert any of these to syringe units in the dosage calculator.
Side effects compared
- ▲Injection site redness, soreness or small lumps
- ▲Mild muscle aches or fatigue for a day after a dose
- ▲Low grade fever or chills in a small minority
- ▲Transient nausea
- ▲Rare rash or itching away from the injection site
- ▲Fatigue, lethargy or a head rush for a few hours after larger doses
- ▲Headache
- ▲Injection site redness or mild bruising
- ▲Nausea or flushing shortly after a dose
- ▲Occasional lightheadedness on standing
Which should you choose?
Thymosin alpha-1 is the fit when the goal is immune function: chronic viral infection, repeated infections, poor vaccine response, or support during recovery from a serious illness. The approved dosage is 1.6 mg subcutaneously twice weekly; community protocols report 0.5 to 1.6 mg two to three times weekly for 4 to 12 weeks. It has thousands of trial patients behind it and a mild side effect profile, mostly injection site redness. It does nothing for a tendon.
TB-500 is the fit when the goal is tissue: a soft tissue injury, stiffness, or recovery across several sites at once. Reported protocols load at 2 to 2.5 mg twice weekly for 4 to 6 weeks, then drop to 2 mg every 1 to 2 weeks or stop. The evidence is rodent, horse and anecdote; no human trial has tested the fragment for injury. It does nothing for immunity, and the theoretical cancer concern from cell migration applies to it specifically.
Pick by the problem, because the two do not overlap. An injury that is not healing, a tendon, a strain, several nagging sites at once: that is TB-500, usually alongside BPC-157, and the choice between those two is at BPC-157 vs TB-500. Frequent infections, a chronic viral problem, a weak response to vaccines, or recovery from a long illness: that is thymosin alpha-1, and it is the better supported compound of the two by a wide margin, with randomized trials and an approval abroad. If someone tells you TB-500 is good for immunity or that thymosin alpha-1 heals tendons, they have swapped the names. The two are compatible and some recovery protocols run both, with no known interaction, but there is no reason to buy one hoping it does the job of the other. Both are prohibited by WADA. Before paying, read the vial: the names are close enough that mislabeling happens, and the doses are different. This page is educational; see best peptides for immune support and best peptides for healing for where each one ranks.
Stacking: Not a natural pair, but compatible. Some recovery protocols run TB-500 for tissue repair alongside thymosin alpha-1 for immune support, with no known interaction and no trial of the combination.
Thymosin alpha-1 is a 28 amino acid peptide originally isolated from the thymus that primes T cells and dendritic cells. It is a licensed drug in much of the world for chronic hepatitis B and immune support, and in the research market it is used for infections, immune weakness and general resilience.
TB-500 is a synthetic version of the active region of thymosin beta-4, a protein found in nearly every human cell that regulates actin and cell movement. It is used for injury recovery, flexibility and general tissue repair, usually alongside BPC-157.
Thymosin Alpha-1 vs TB-500: frequently asked
Is thymosin alpha-1 the same as TB-500?
No. Thymosin alpha-1 is a 28 amino acid immune peptide and an approved drug in more than 30 countries. TB-500 is a short fragment of thymosin beta-4, a cell structure protein, used for injury recovery and approved nowhere. They share the thymosin name because both were first isolated from thymus extract, and nothing else. Different target, different dose, different reason to buy.
Can you take thymosin alpha-1 and TB-500 together?
Yes, and some recovery protocols do, with TB-500 for tissue repair and thymosin alpha-1 for immune support during a long rehab or after an illness. No interaction is known and no trial has tested the pair. The schedules happen to line up, since both are dosed twice weekly, but they are usually kept in separate syringes so any injection reaction can be traced.
Which is better for healing, thymosin alpha-1 or TB-500?
TB-500, because thymosin alpha-1 has no tissue repair effect at all. TB-500 regulates actin and cell migration into a wound, with rodent and veterinary evidence for tendon and ligament recovery. For a single localized injury BPC-157 is the usual first choice and TB-500 is added for diffuse or multi site problems; see the BPC-157 and TB-500 stack.
Is thymosin alpha-1 FDA approved?
No. SciClone pursued approval mainly in Asia and Europe, where hepatitis B is more common, and a US phase 3 trial in hepatitis C did not meet its endpoint. In 2023 the FDA placed it in Category 2 of the bulk substances list, which blocked compounding. The February 2026 HHS announcement signaled an intent to move most Category 2 peptides back toward Category 1, and thymosin alpha-1 was not among the five reported as staying restricted, but that is stated intent rather than a final rule. See the FDA peptide compounding list for 2026.
Is TB-500 the same as thymosin beta-4?
TB-500 is a marketing name that usually refers to a synthetic 7 amino acid fragment, LKKTETQ, taken from the actin binding region of thymosin beta-4. Thymosin beta-4 is the full 43 amino acid protein, which is what RegeneRx took through phase 2 trials as eye drops. Some vendors ship the full protein under the TB-500 label, so the two names overlap in practice even though they are not the same molecule.
Does WADA prohibit thymosin alpha-1 and TB-500?
Both. TB-500 is prohibited and is widely screened for, including in horse racing. Thymosin alpha-1 is treated as prohibited under the S0 non approved substances heading, and athletes have been sanctioned for it. The broader question of what shows up in testing is covered at do peptides show up on a drug test.
Related reading
Soft tissue and tendon injury recovery
Skin, scar and post-procedure healing
Healing with inflammation and gut support
Immune support and chronic infection
Which healing peptide should you start with, and do you need both?
Dosage
Sources
- Thymosin alpha 1 in the treatment of chronic hepatitis B: a meta-analysis. Alimentary Pharmacology and Therapeutics, 2001
- Thymosin alpha 1: a historical overview. Annals of the New York Academy of Sciences, 2007
- Thymosin beta 4 accelerates wound healing. Journal of Investigative Dermatology, 1999
- Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature, 2004