The FDA Reversed Itself on Estrogen. Why Did it Take Twenty Years?

By: Gustav Lo, MD | Chief Medical Officer

For over 20 years, the FDA told women that estrogen increases the risk of breast cancer. Definitively.

Doctors (including me, for a while) repeated this. It was amplified in headlines. Hormone replacement — once widely prescribed — became rare.

That all changed on November 10 2025. The FDA commissioner not only announced the removal of the breast cancer warning on estrogen products, but also stated outright that this false warning was “one of the biggest mistakes in modern medicine.” He cited research well-known in my field that hormone replacement in women reduces health risks dramatically, including heart attacks, strokes, fractures, and dementia. An entire generation of women was needlessly scared away from hormone replacement, and their enjoyment of life and their health outcomes suffered because of it.

So the obvious question:

Why didn’t we know this 20 years ago?

The uncomfortable answer is that, in some ways, we did.

When the Women’s Health Initiative (WHI) study results were released in 2002, the headlines were dramatic: hormones cause breast cancer and heart disease. Prescriptions plummeted almost overnight. Millions of women stopped therapy immediately. Many of my patients suffered that sudden misery.

What received far less attention were the study’s limitations. The population was older than typical menopause patients. The formulation included synthetic progestins. And within just a few years, re-analysis of the same data revealed something very different: women who began hormone therapy closer to menopause had reduced cardiovascular risk, and women using estrogen without synthetic progestins did not have increased breast cancer risk — some analyses even suggested a reduction.

It was already too late. Patients remember headlines. Once a message like “hormones cause cancer” becomes embedded in public consciousness, reversing it is extraordinarily difficult. Women knew about it, and so did their doctors. Hormone therapy went from about 30% of menopausal women to about 1%. Osteoporotic fractures increased. Millions of women suffered symptoms like hot flashes, sleep disruption, mood changes, sexual dysfunction, and rapid bone loss. Many women entering menopause were told to “just live with it.”

As a physician focused on optimizing healthspan, I see this as a tragedy hiding in plain sight. Menopause is, biologically speaking, a hormone deficiency syndrome. When women lose hormones their tissues rely on, those tissues begin to deteriorate — in the cardiovascular system, brain, bone, and genitourinary tract. This is well-known. Yet an entire generation was told that replacing their natural hormones was inherently dangerous.

The 50s are a critical prevention window. Rates of fractures, heart attacks, strokes, and dementia are certainly higher than they should have been. Beyond that is the quieter suffering: urinary complaints, sexual dysfunction, loss of energy, poor sleep, brain fog. How many women stepped back from careers because they “couldn’t bring it” (I’ve met a few)? How many relationships strained? And the most important — how many lives were shortened?

This story is not about villainy; I’m not calling for abandoning regulatory oversight. But we need to be open about the losses society has experienced from “one of the biggest mistakes in modern medicine,” and demand some humility from the regulatory agencies and research organizations at the core of this system.

“Scientific consensus” at regulatory agencies like the FDA often amounts to a show of hands around a table – not really the eternal truth it’s made out to be. We need to build a system that responds faster when evidence changes — so women don’t have to wait another generation to fully enjoy the second half of their lives.

Oh and what about MEN? Well that’s another story…

– Gustav Lo, MD

Gustav Lo, MD, is the Chief Medical Officer and Founder of RegenCen and Cosmetic Skin & Laser Center (CSLC) which he established in 2001 with Courtney Lo, PA. With over 30 years of experience as a physician and a passion for innovation, Dr. Lo has transformed CSLC and RegenCen into a nationally recognized medical practice focused on optimizing healthspan.

A passionate educator and advocate for women’s health, Dr. Lo regularly speaks on the benefits of hormone optimization, working to dispel outdated myths and empower women with safer, modern options.