ENDO-205: A Non-Hormonal Endometriosis Peptide
A first-in-class peptide designed to trigger cell death only inside endometriosis lesions. The FDA cleared its IND for first-in-human trials in 2026 — here is what the peer-reviewed evidence supports today, and what remains unproven.
How It Works
Endometriotic lesions resist apoptosis — programmed cell death — which lets them persist and spread; survival pathways such as PI3K/Akt are implicated. ENDO-205 is designed to force apoptosis selectively inside lesion tissue.
Almost every approved medical therapy for endometriosis works by suppressing ovarian hormones, which limits long-term use and fertility. ENDO-205 is developed to avoid hormonal manipulation entirely.
Ectopic lesions survive in a hostile, hypoxic peritoneal microenvironment distinct from healthy tissue. EndoCyclic Therapeutics reports ENDO-205 senses a microenvironmental difference (a pH trigger) so it acts only in diseased tissue — a company claim not yet in the peer-reviewed literature.
The FDA cleared ENDO-205’s IND in 2026 for a first-in-human study in healthy pre-menopausal volunteers. Phase 1 tests safety and dosing — not whether it treats endometriosis.
What the Data Shows
Key Takeaways
- ENDO-205 is a first-in-class, non-hormonal peptide therapeutic for endometriosis; the FDA cleared its Investigational New Drug application in 2026 for a first-in-human Phase 1 study.
- It is designed to induce apoptosis (programmed cell death) selectively in endometriosis lesions, acting only in diseased tissue.
- Endometriosis affects roughly 10% of reproductive-age women — about 190 million worldwide by WHO estimate (~176 million in peer-reviewed figures).
- Resistance to apoptosis is an established driver of lesion survival and growth in endometriosis.
- Current therapies are largely hormonal or surgical, have limited long-term efficacy and notable side effects, and are associated with high recurrence — a genuine unmet need.
- About a third of women do not respond to first-line progestins or oral contraceptives.
- Whether ENDO-205 actually reduces endometriosis symptoms or lesions in humans — the Phase 1 trial enrolls healthy volunteers and tests safety, not efficacy.
- Its preclinical "lesion elimination" results are company-reported and not yet published in the peer-reviewed literature.
- Long-term safety, the effect on fertility, dosing, and durability of any benefit are all unknown.
- How the reported lesion-selective (pH/microenvironment) mechanism performs in the complex human peritoneal environment.
- When — or whether — it reaches market; first-in-human clearance is years from any approval.
- It is not available to buy or prescribe anywhere; anything sold as "ENDO-205" is not the investigational drug.
Frequently Asked Questions
What is ENDO-205?
ENDO-205 is a first-in-class, non-hormonal peptide therapeutic in development for endometriosis. The FDA cleared its Investigational New Drug application in 2026, allowing a first-in-human Phase 1 study. It is designed to trigger apoptosis (programmed cell death) selectively in endometriosis lesions.
How does ENDO-205 work?
It is designed to induce programmed cell death only inside endometriotic lesions rather than suppressing hormones. The developer describes a mechanism that senses a difference in the lesion microenvironment (a pH trigger). This targets established biology: endometriotic lesions resist apoptosis and survive in a hostile, hypoxic peritoneal microenvironment.
Is ENDO-205 FDA-approved or available to buy?
No. The FDA cleared ENDO-205 to begin Phase 1 human trials — that is not the same as approval. It is investigational, not marketed, and not available for purchase or prescription anywhere.
Is ENDO-205 hormonal like most endometriosis drugs?
No — it is non-hormonal, which is what makes it notable. About a third of women fail first-line hormonal therapy, and hormonal options limit fertility and long-term use, so a non-hormonal, lesion-targeted approach addresses a real unmet need.
When will ENDO-205 be available?
Unknown. Phase 1 is the first of several trial stages; efficacy in patients has not yet been tested. If it succeeds through Phase 2 and 3 and is approved, availability would still be years away.
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Peer-Reviewed References
Educational purposes only. Not medical advice.
ENDO-205 is an investigational drug that is not approved by the FDA and not available for purchase or prescription. Consult a qualified clinician about endometriosis care.