Thymosin alpha-1 vs Semax
A peptide sold by wellness clinics as an immune booster. Trials show a modest effect in hepatitis B, and a large sepsis trial found none. A nasal spray sold to sharpen memory and protect the brain after stroke. Studies from Russia look promising, but none was a proper blinded trial.
Both sit at grade B: some human evidence. Neither is FDA approved.
Evidence
BSome human evidence
BSome human evidence
Human studies cited
Animal or cell studies cited
Why the grade
Thymosin alpha-1 has several randomized trials in chronic hepatitis B (98 and 316 patients) and a meta-analysis of five trials with 353 patients showing delayed viral suppression, which is the approved use abroad. The 1,106-patient TESTS phase 3 trial in sepsis found no mortality benefit. The general immune-boosting use it is sold for in the US has no controlled trials, so the compound grades B on its hepatitis B evidence and D on the wellness claims.
Five Russian clinical studies cover stroke (30 patients versus 80 controls in 1997; 110 patients in 2018), chronic cerebrovascular insufficiency (187 patients), optic nerve disease and a 24-person imaging study in healthy volunteers. Several had control groups but none describes randomization and blinding in the way a modern trial would, and none has been replicated outside Russia. Controlled human studies exist, so B, but at the weak end.
FDA
Not approved
Thymosin alpha-1 is not approved by the FDA for any use. It is approved as thymalfasin (Zadaxin) in more than 35 other countries for hepatitis B and C and as an immune adjuvant. In the United States it was taken off the FDA's Category 2 compounding list after its nominators withdrew it, and in December 2024 the Pharmacy Compounding Advisory Committee voted 17 to 4 against adding it to the 503A bulks list; it is sold online as a research chemical.
Not approved
Semax is not approved by the FDA for any use and is sold in the United States as a research chemical. It is registered as a prescription drug in Russia. In July 2026 the FDA's Pharmacy Compounding Advisory Committee voted to recommend adding semax to the list of substances pharmacies may compound, against the advice of FDA staff. On 28 October 2026 HHS issued an enforcement discretion policy covering semax as a nasal product only, compounded by licensed pharmacies and physicians for named patients under sourcing, testing, labeling and reporting conditions. That is not an approval.
Sold for
Thymosin alpha-1 is sold by wellness clinics as an immune-system booster for infections, cancer support, autoimmune disease and long COVID.
Semax is sold as a nasal nootropic that sharpens memory and attention and protects the brain after stroke.
Studies say
Randomized trials support a modest, delayed antiviral effect in chronic hepatitis B, a large trial found no benefit in sepsis, and there are no trials of the immune-boosting uses marketed in the US, which is why it grades B.
Russian clinical studies report faster recovery after stroke and fewer vascular events in chronic cerebrovascular disease, and a small imaging study shows it changes brain network activity in healthy people, but no blinded placebo-controlled trial has been published, so the cognitive claims are unproven.
Class
Immunomodulatory peptide
Nootropic peptide (ACTH(4-10) analog)
Route
Injection
Nasal