No. Thymogen is not thymosin alpha 1. Thymogen is a two-amino-acid peptide. Thymosin alpha 1 has 28. They came out of the same calf thymus research, and that is the whole connection.

If you came here to find out whether the dosage numbers, benefits and side effects you read about thymosin alpha 1 apply to Thymogen, the answer is no. Different molecule, different research, different rules.

And here is the part almost no vendor page mentions: Thymogen already failed a 202-patient, placebo-controlled human trial. It ran under a different name.

Jump to what you need

• What is Thymogen?
• Why do people think it’s thymosin alpha 1?
• Why doesn’t “99% pure” prove much?
• Has Thymogen been tested in people?
• What does the Russian and animal research show?
• How do you check a certificate of analysis?
• Is Thymogen legal?
• Sources

What is Thymogen?

Thymogen is a synthetic dipeptide: glutamic acid joined to tryptophan, both in the L form.

Researchers pulled it out of Thymalin, a calf thymus peptide mixture, using reverse-phase HPLC. Then they made it synthetically and named it Thymogen.

You will see it sold under six or seven names. They are all the same molecule.

Sequence	L-Glu-L-Trp (EW)
Size	2 amino acids
Formula	C16H19N3O5
Molecular weight	333.34 g/mol
CAS	38101-59-6
PubChem CID	100094
Also sold as	Oglufanide, Timogen, Thymagen, IM-862, EW dipeptide

Two amino acids is small. Small enough to matter: your body carries dipeptidases, enzymes whose job is to chop dipeptides into free amino acids. Any claim about what Thymogen does after it enters the bloodstream has to survive that.

Why do people think Thymogen is thymosin alpha 1?

Because a 1990s US patent said Thymogen was the active ingredient in a thymus extract called thymosin. That line got copied for thirty years.

It isn’t true in the way people now read it. Both compounds were found in bovine thymus fractions. That’s the relationship. Neither is a version of the other.

Four different things get blended together on product pages. Here is what each one actually is.

If you see this name	It means this
Thymogen	One synthetic dipeptide, L-α-Glu-L-Trp. 2 amino acids.
Thymalin	A calf thymus peptide mixture. Not a single molecule.
Thymosin alpha 1	A separate 28-amino-acid peptide. Sold internationally as thymalfasin (Zadaxin).
Thymodepressin	The D-form dipeptide. Studied as an immune suppressor.

Can you use thymosin alpha 1 dosage numbers for Thymogen?

No. You would be applying numbers from a 3,100-dalton peptide to a 333-dalton one.

Every search for a thymosin alpha 1 dosage chart, protocol, or “what to take when sick” is a search about the other molecule. It has its own pharmacokinetics, its own trial record, its own regulatory file.

The transfer fails in both directions. Thymosin alpha 1 is approved in more than 35 countries for chronic hepatitis B. Thymogen is not that drug, and does not inherit that record.

Why doesn’t a “99% pure” certificate prove much?

Because Thymogen’s mirror image weighs exactly the same — and does the opposite thing.

Flip the shape of both amino acids and you get Thymodepressin. Same formula. Same mass. Opposite direction.

Thymogen

C₁₆H₁₉N₃O₅

333.34 g/mol

L-α-Glu-L-Trp

Immune stimulant

Thymodepressin

C₁₆H₁₉N₃O₅

333.34 g/mol

D-γ-Glu-D-Trp

Immune suppressant

Grey lines are identical in both. Red lines are the difference — and a mass spectrum cannot see either of them.

This was not a small shift in potency. Researchers describe the pair as the first example of two mirror-image drugs regulating the same system in opposite directions. Reversing both centres didn’t just remove the stimulating effect; the D forms became inhibitors under the same conditions where the L forms stimulated.

The two marketed drugs aren’t even clean mirrors. Thymodepressin also attaches at a different point on the glutamic acid — the γ bond instead of the α.

So what does a purity percentage tell you? How much of one peak is in the vial. Not which molecule that peak is. A batch can be 99.4% pure and 99.4% wrong.

Has Thymogen been tested in people?

Yes. More rigorously than almost any peptide in this category. The results were not good.

The trials ran under the name IM862 (oglufanide disodium), which is why they don’t show up if you only search “Thymogen.”

Study	What happened
Phase I/II, AIDS-related Kaposi’s sarcoma	36% response rate. Minimal toxicity. Promising.
Randomised nasal study, 44 patients	Difference between arms was not statistically significant.
Phase III, 202 patients, placebo-controlled	23% response on drug vs 21% on placebo. No significant difference. Shorter time to response, but also shorter time to progression — the authors concluded it may accelerate progression.
Phase II, metastatic renal cell carcinoma	Confirmed the lack of significant toxicity.
Phase II, hepatitis C	Entered on the strength of its antiangiogenic and immune-modulating profile.

Read that honestly and it cuts both ways.

Thymogen has been through randomised, double-blind, placebo-controlled testing. Most research peptides have nothing close. That is a genuine point in its favour.

The efficacy signal did not survive. The tolerability signal did — low toxicity is the most repeatable finding across every one of these studies.

“Well tolerated” and “works” are two different claims. Only one of them held up.

What does the Russian and animal research show?

Thymogen was registered as a drug in Russia in 1990 and appears in the Russian Pharmacopoeia. Reported mechanisms include changes to lymphocyte differentiation and to the T-helper / T-suppressor ratio.

That is a real regulatory history. It is not a modern efficacy file. 1990 approval standards are not the standards that produced the 2005 phase III — which is exactly why the phase III carries more weight, not less.

The animal work is separate again. A 2000 rat study reported activated T-cell differentiation and neutrophil activity, then tracked survival and spontaneous tumours in female rats over 12 months. Secondary summaries describe 76 rats dosed at 5 micrograms, five times a week, with lower tumour incidence than controls.

Rats. Micrograms. One year. That’s a hypothesis about ageing, not a human outcome.

The “more than 25 million patients treated” figure you’ll see quoted has no published patient registry behind it that I could find. Treat it as marketing arithmetic until someone shows the denominator.

How do you check a certificate of analysis?

For this molecule, a purity number answers the wrong question. Here is what to look for instead, and why each item earns its place.

Look for	Why it matters
The name spelled out: L-α-glutamyl-L-tryptophan	“Glu-Trp” alone is ambiguous by exactly the margin that matters.
Chiral analysis, or a reference standard	This is the only check that separates Thymogen from Thymodepressin. Most COAs skip it.
The bond position (α, not γ)	Same reason. Same mass, different molecule.
A chromatogram, not a percentage	You want the trace, the method and the peak integration — the number on its own is unverifiable.
A peptide content assay	Net peptide is routinely 10–25% below the gross fill weight. Purity does not show this.
Water, counterion and residual solvent data	This is where the missing mass usually hides.
A lot number that matches the vial	Plus a named lab you can actually contact. Otherwise the document is decoration.
Sterility and endotoxin, if relevant	Purity testing covers neither.

The question to ask a supplier: can you show that this lot contains L-α-Glu-L-Trp — not just something weighing 333 daltons?

If the answer is a purity percentage, the identity is unverified.

Is Thymogen legal?

Thymogen is not an approved drug in the United States or the EU. What’s sold online is labelled research-use-only, which is a legal category, not a quality claim. It tells you nothing about what’s in the vial.

Thymosin alpha 1 sits in a different but equally awkward spot: never FDA-approved in the US, and placed in Category 2 of the interim 503A bulk substances list in September 2023.

Neither compound has an over-the-counter route. If you’re researching immune peptides for a real medical situation, that conversation belongs with a clinician who can see your labs. Nothing here is medical advice, and nothing here is a protocol.

What it adds up to

• Thymogen is a 2-amino-acid peptide. Thymosin alpha 1 is a 28-amino-acid peptide. They are not interchangeable, and neither are their dosages.
• Its mirror image weighs the same and suppresses instead of stimulates. Purity testing cannot tell them apart.
• It has real human trial data, under the name IM862 — and the trial failed its endpoint.
• Low toxicity is the finding that has held up across every study.
• Ask for chiral identity, not purity.