In this final episode of the Progesterone Promise series, Dr. Brendan McCarthy, Chief Medical Officer of Protea Medical Center, breaks down one of the most misunderstood hormones in women’s health: progesterone.
Progesterone is not “good” or “bad.” It’s contextual.
In today’s world of quick sound bites and social media medicine, hormones are often reduced to oversimplified claims like “progesterone fixes anxiety” or “progesterone causes breast cancer.” The truth? It depends on your body, your stress levels, your liver health, your inflammation, your delivery method, and whether you're using bioidentical progesterone or synthetic progestins.
Citations:
Claim:
Oral micronized progesterone undergoes significant hepatic first-pass metabolism, increasing neuroactive metabolites (especially allopregnanolone), which positively modulate GABA-A receptors and produce sedative/anxiolytic effects.
Core Evidence:
Simon et al., 1993; de Lignières et al., 1995; Freeman et al., 1990 — Oral progesterone produces measurable neuroactive metabolites.
Paul & Purdy, 1992; Rupprecht et al., 2001 — Allopregnanolone enhances GABA-A receptor activity.
Supports:
Sedation variability by route • Neurosteroid generation • GABA-A modulation
2. Sulfation vs 5α-Reduction → Opposing Neurologic Effects
Claim:
Progesterone metabolites can produce calming (5α-reduced) or excitatory (sulfated) neurologic effects depending on enzyme routing.
Core Evidence:
Majewska et al., 1990 — Pregnenolone sulfate negatively modulates GABA-A.
Wu et al., 1991 — Sulfated neurosteroids enhance NMDA signaling.
Schumacher et al., 2007; Reddy, 2010 — Pathway reviews of sulfation vs 5α-reduction.
Supports:
Reverse responding hypothesis • Divergent neurologic experiences • Enzyme-dependent effects
3. Stress & Enzyme Modulation
Claim:
Chronic stress alters HPA axis tone and hepatic enzyme expression, influencing steroid metabolism balance.
Core Evidence:
McEwen, 1998 — Allostatic load model.
Charmandari et al., 2005 — Cortisol’s systemic regulatory effects.
Zanger & Schwab, 2013; Gibson & Skett, 2001 — Stress alters cytochrome P450 expression.
Supports:
Stress-biased metabolism • Context-dependent hormone response
4. Breast Tissue Signaling & Context
Claim:
Progesterone influences mammary differentiation and interacts with estrogen signaling in context-dependent ways.
Core Evidence:
Brisken & O’Malley, 2010 — Progesterone receptor biology in breast tissue.
Beleut et al., 2010 — RANKL mediates progesterone-driven proliferation.
Hofseth et al., 1999 — PR-ER signaling interaction.
Stanczyk & Bhavnani, 2014 — Natural vs synthetic differences in breast effects.
Supports:
Lobuloalveolar differentiation • RANKL pathway • Context-dependent proliferation
5. Synthetic Progestins vs Bioidentical Progesterone
Claim:
Synthetic progestins differ structurally and bind off-target receptors, producing distinct tissue effects.
Core Evidence:
Stanczyk et al., 2013 — Receptor binding differences.
Sitruk-Ware, 2004 — Biologic comparisons.
Chlebowski et al., 2003 (WHI) — Breast cancer signal with CEE + MPA.
Supports:
Structural divergence • Receptor-level differences • WHI clarification
6. Route of Delivery Differences
Claim:
Oral, vaginal, transdermal, and sublingual progesterone produce distinct pharmacokinetic profiles and tissue targeting.
Core Evidence:
Simon, 1995 — Oral vs vaginal PK comparison.
Cicinelli et al., 2000 — “First uterine pass effect.”
Wren et al., 2003 — Route-dependent systemic levels.
Supports:
Uterine targeting • Neurosteroid variability • Sedation differences
7. Progesterone, PMS & Migraine
Claim:
Neurosteroid fluctuations influence GABAergic tone and may contribute to PMS and migraine susceptibility.
Core Evidence:
Backstrom et al., 2011 — Allopregnanolone fluctuations in PMS.
Reddy & Rogawski, 2002 — Neurosteroids and seizure threshold.
Martin & Behbehani, 2001 — Hormonal fluctuations and migraine.
Supports:
Luteal neurosteroid shifts • GABA instability • Migraine association
Dr. Brendan McCarthy is the founder and Chief Medical Officer of Protea Medical Center in Arizona. With over two decades of experience, he’s helped thousands of patients navigate hormonal imbalances using bioidentical HRT, nutrition, and root-cause medicine. He’s also taught and mentored other physicians on integrative approaches to hormone therapy, weight loss, fertility, and more. If you’re ready to take your health seriously, this podcast is a great place to start.
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📘 Read Dr. McCarthy’s Book: Jump Off the Mood Swing – A Sane Woman’s Guide to Her Crazy Hormones https://www.amazon.com/Jump-Off-Mood-Swing-Hormones/dp/0999649604
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Website: www.protealife.com
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