Isomolecular Hormones (IMH)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 7, 2026

Isomolecular hormones are compounds whose molecular structure is identical to hormones produced endogenously by the human body, including progesterone, 17β-estradiol, and testosterone. Dr. Thomas Hilgers coined and preferred the term "isomolecular" over the more commonly used "bioidentical," because it specifies the actual criterion: molecular identity, not a vague natural-versus-synthetic distinction.⁷⁸

In NaProTECHNOLOGY practice, isomolecular hormones are the pharmacological standard for all hormone replacement and supplementation protocols. This includes oral micronized progesterone (sustained-release) for CPRT, 17β-estradiol for CERT, postpartum progesterone protocols for mood support, and pregnancy-maintenance progesterone in the prematurity prevention program. The pregnancy safety profile of isomolecular progesterone is supported by published outcomes data.⁸²

Hilgers distinguishes isomolecular hormones from heteromolecular artimones, the synthetic progestins and estrins found in oral contraceptives and most conventional hormone replacement therapy. The molecular difference is not cosmetic. It affects receptor binding, downstream signaling, and clinical side-effect profiles. NaPro protocols do not substitute one for the other.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.