Most of us have absorbed one fact about hormone therapy: it causes breast cancer. A friend’s mother stopped taking it in 2002. A doctor said no without much explanation. The pamphlet had a warning box. That fact came from one study, it was half-right for one group of women, and the thinking has moved a long way since. This is the story, with the numbers, so you can have the conversation properly.
Three hormones matter here, and they don’t all leave at once.
Estrogen is the one everyone knows. The form your ovaries make is estradiol, and it does far more than run your cycle. It holds the brain’s thermostat in a steady range, keeps bone dense, keeps the lining of the vagina and bladder thick and moist, drives collagen in skin and tendons, influences where fat is stored, and keeps blood vessels supple. Through your 40s the ovaries’ output becomes erratic before it falls, high one month and low the next, which is why perimenopause often feels more chaotic than menopause itself. That reach is also why falling estrogen shows up in so many unrelated places.
Progesterone is the hormone of the second half of the cycle. It’s made by the ovary only after an egg is released, and it does two jobs. In the brain it’s calming: it’s broken down into a substance that acts on the same receptors as sedatives, which is why it helps sleep and steadies mood, and why its absence can be felt as anxiety and 3 a.m. waking. In the uterus it’s the brake on estrogen. Estrogen’s message to the uterine lining is grow; progesterone’s is stop growing, get organised, and shed on schedule. In the 40s, more and more cycles pass without an egg being released, and in those cycles no progesterone is made at all. So the brake goes first, before estrogen does: sleep and mood wobble, and the lining keeps building under estrogen with nothing to stop it and nothing to trigger a timely period, so it sheds late, unevenly and heavily. This is also why, in hormone therapy, anyone taking estrogen who still has a uterus takes progesterone with it. Lining that grows unchecked for years becomes thick and disordered, a state called hyperplasia that can progress to cancer of the uterine lining; progesterone prevents it.
Testosterone is not just a male hormone: women make it in the ovaries and adrenal glands, and before menopause you have more testosterone in your blood than estrogen. It drives sexual desire and arousal, contributes to energy, motivation and mood, and helps maintain muscle and bone. It declines with age rather than with menopause, falling steadily from the 20s so that levels are roughly half by the mid-40s. Menopause doesn’t remove it the way it removes estrogen, and whether and when to treat it is a separate conversation, which we cover in its own article.
The Women’s Health Initiative (WHI) was a large randomised trial run by the US National Institutes of Health, and it asked a question that had nothing to do with treating menopause: would hormones prevent heart disease in older women? To answer it, the WHI ran two trials side by side. In the first, 16,608 women who still had a uterus were given either a placebo or the standard prescription of the day: conjugated equine estrogen (Premarin, made from pregnant mares’ urine) paired with medroxyprogesterone acetate, a synthetic progestin. In the second, 10,739 women who’d had a hysterectomy were given either a placebo or the same estrogen on its own, since without a uterus there’s no lining to protect and no need to take progesterone. In both, the average age at enrolment was 63, and most were more than ten years past menopause4,5.
The combined estrogen-and-progestin trial was stopped early in July 2002 because the hormone group had more breast cancer, heart attacks, strokes and blood clots, and it was reported the way that makes the biggest headline: a 26% increase in breast cancer, 41% in stroke, a doubling of clots. Prescriptions collapsed. Hormone therapy use among postmenopausal women in the US fell from about 27% in 1999 to 5% by 20202, Canada followed, a generation of women went untreated, and a generation of doctors was trained to say no.
What the trial actually showed, and still shows, is narrower than the headline. Pairing estrogen with that particular synthetic progestin, in women who were mostly in their 60s and 70s, raised breast cancer risk. Starting hormones for the first time a decade or more after menopause raised cardiovascular risk. Neither of those describes a 49-year-old with night sweats, and neither of those is how hormone therapy is prescribed now. The rest of this article is about how we know that.
The WHI never stopped following its participants, and the picture changed as the follow-up lengthened.
Mortality. After 18 years, women who had been assigned to hormone therapy were no more likely to have died than women on placebo, from any cause, from cardiovascular disease, or from cancer6.
Breast cancer split in two. The second trial, the one that gave estrogen alone to women who’d had a hysterectomy, found the opposite of the first. After more than 20 years of follow-up, women who took estrogen alone had 22% less breast cancer than placebo and 40% fewer breast cancer deaths. The lesson the researchers drew was that the progestin, not the estrogen, had been carrying the risk5.
The progestin matters. A large French study run by the national health research institute, INSERM, which followed about 80,000 women for eight years, found that estrogen combined with micronized progesterone, which is chemically identical to the body’s own, showed no increase in breast cancer over the study period, while estrogen combined with synthetic progestins raised it by about two-thirds8. This was an observational study, where women chose their own therapy, so it can’t prove cause the way the WHI could, but it is the single most important reason modern prescribing looks different from 2002: in Canada, the standard progesterone now is micronized progesterone, not medroxyprogesterone.
Timing matters. Re-analysis of the WHI by age showed that women who started within ten years of menopause, or before 60, did not see the cardiovascular harm that older starters did, and may have seen benefit. A University of Southern California trial of 643 women then tested this directly. It split women by how long they’d been past menopause, under six years or ten years and more, and within each of those gave half estradiol and half a placebo. Among the early starters, artery walls on estradiol thickened at about half the rate of those on placebo; among the late starters, estradiol and placebo were no different9. This is the “timing hypothesis,” and it’s why every major guideline now describes a window: starting hormone therapy under 60, or within ten years of your last period, is where the benefits clearly outweigh the risks, and starting for the first time outside that window needs a much harder look. It doesn’t mean starting before menopause for its own sake; the reason to start is symptoms, and for most women those arrive well inside the window1,3.
What about the studies that say otherwise? You may hear that a large 2019 analysis found every form of hormone therapy raised breast cancer risk. In 2020, five of the field’s major professional bodies, the International Menopause Society, the British, European and Australasian menopause societies, and the UK’s Royal College of Obstetricians and Gynaecologists, issued a joint statement saying that analysis should not be applied to modern regimens: the women in it were overwhelmingly on the older 2002 combination, very few had taken micronized progesterone, and the French study above wasn’t included at all7,14. The North American society, the largest of them, reached the same view in its own 2022 statement1. The best evidence on the combination now prescribed, estradiol with micronized progesterone, comes from that French study’s 2014 follow-up, observational again8. In the first five years of hormone therapy, no measurable increase in breast cancer. Beyond five years, a real one: over the twenty years from 50 to 69, roughly six women in a hundred diagnosed becomes seven or eight. However, once women stop, the difference disappears. That’s the trade-off a careful doctor has in mind for the therapy you’d actually be offered, and it’s why no guideline sets a hard stop date but every one says reassess as you go.
Risk on its own is half a decision, and the benefit that gets the least attention is bone.
Bone is constantly being broken down and rebuilt, and estrogen is what keeps the breaking-down side in check. When it falls, breakdown outruns rebuilding and bone density drops fastest in the first five to seven years after menopause, before settling to a slower decline. Estrogen therapy holds that loss off for as long as you take it, and both the Canadian and North American guidelines list preventing bone loss and fractures as one of its established benefits1,3. It doesn’t build permanent bone, though, and the steep phase is triggered by losing estrogen whenever that happens. Studies that followed women after they stopped found the protection against fracture fades within a few years15. So what it buys is time, not immunity. The bone loss still happens; it happens later, and every year it’s pushed back is a year of moving freely, staying active and living independently. For women who stay on it, the protection continues.
Then there is the reason most women take it: sleeping through the night, not flushing in a meeting, sex without pain, joints that stop aching. Untreated symptoms carry their own costs, to work, relationships, mood and exercise, and those compound over the decade or so that symptoms last. The Canadian guideline (SOGC) and the North American one (The Menopause Society) both weigh these against the risks above and reach the same position: for a woman under 60, or within ten years of her last period, who has symptoms that bother her, hormone therapy is a reasonable first-line option, and the decision is hers to make with her clinician, based on her own symptoms, history and priorities1,3. Neither recommends it for a woman without symptoms, for prevention alone.
The Menopause Society’s 2022 position statement, the reference document for North America, puts it plainly: for women under 60 or within ten years of menopause who have bothersome symptoms, the benefits of hormone therapy outweigh the risks. It’s the most effective treatment for hot flashes and night sweats, it prevents bone loss and fractures, and it treats vaginal and urinary symptoms. The breast cancer risk with combined therapy is described as rare: fewer than one additional case per 1,000 women per year. There is no fixed date by which you must stop; the advice is to reassess periodically and, as you age, consider lowering the dose and switching from a pill to a patch or gel, which carries less risk of blood clots (more on that below)1.
The Society of Obstetricians and Gynaecologists of Canada (SOGC) says the same in its 2021–22 menopause guideline series, which is what Canadian doctors are trained against, and it rates that recommendation as strong, on high-quality evidence3.
Two things happened recently that you may have seen in the news. In November 2025 the US Food and Drug Administration (FDA) removed the “black box” warning about breast cancer, heart disease and dementia from estrogen products, saying the risks had been overstated for the women who actually use them; the one warning kept is about endometrial cancer for women who take estrogen without progesterone while they still have a uterus2. And on March 1, 2026, BC PharmaCare began covering estradiol patches, gels and tablets, micronized progesterone and vaginal estrogen in full for anyone with BC medical coverage (MSP)11.
Patch or gel versus pill. Estrogen swallowed as a pill goes to the liver before it reaches the rest of the body, and the liver responds by making more of the proteins that help blood clot. Estrogen from a patch or gel is absorbed through the skin straight into the bloodstream and skips that first pass, and studies have found no increase in blood clots with patches or gels. So the patch or gel is where anyone with a higher risk of clots or stroke belongs: a family history of clots, migraine with aura, high blood pressure, obesity or smoking. Increasingly it’s the default for everyone1,3.
What’s on the shelf in Canada. Estradiol comes as a patch (Estradot, Climara and generics), a gel (Estrogel, Divigel) and a tablet (Estrace and generics). Progesterone is Prometrium or generic micronized progesterone. Vaginal estrogen comes as a tablet insert (Vagifem), a ring (Estring), a cream (Premarin, Estragyn), plus prasterone (Intrarosa), a vaginal form of the hormone DHEA that the tissue converts to estrogen locally.
Strong evidence, clear benefit. Hot flashes and night sweats: estrogen is the most effective treatment there is. The sleep that flushes were wrecking. Vaginal dryness, pain with sex, urgency and recurrent urinary infections, which respond to local vaginal estrogen even in women who take nothing else. Bone: hormone therapy prevents the rapid bone loss of early menopause and reduces fractures.
Reasonable evidence, often helps. Mood changes that arrived with perimenopause, particularly low mood and irritability tied to the hormonal swings (a new depression is a different thing and needs its own assessment). Joint and muscle aches. Some of the brain fog, mostly through better sleep. Skin, modestly; for hair the evidence isn’t there yet1.
Not an indication. Preventing heart disease. Preventing dementia or treating memory decline: hormone therapy started after 65 increased dementia risk in the WHI’s memory sub-study, and no guideline supports it for the brain at any age. Weight loss: it may slightly blunt the weight gain and belly fat of the transition, but the effect is small and it is not a weight-loss treatment1.
Systemic hormone therapy is generally ruled out with a history of breast cancer or another hormone-sensitive cancer, an unexplained vaginal bleed that hasn’t been investigated, a previous clot in a leg or lung, a stroke or heart attack, or active liver disease3. Migraine with aura and a strong family history of clots don’t rule it out but shape the route and dose; that’s usually where the patch comes in.
Vaginal estrogen sits in a different category. Almost none of it reaches the rest of the body, it needs no progesterone, and the Menopause Society considers it reasonable even after breast cancer, in discussion with the oncologist1,7.
For hot flashes there are now two non-hormonal prescription options in Canada that work on the brain’s thermostat directly: fezolinetant (Veozah), approved by Health Canada in December 2024, and elinzanetant (Lynkuet), approved in July 202512,13. Certain antidepressants (the SSRI and SNRI types, at low doses) and gabapentin also reduce flushes, and cognitive behavioural therapy has good evidence for making them less disruptive. For vaginal symptoms, regular moisturizers and lubricants help many women, and prasterone is a non-estrogen prescription option.
After 40, perimenopause is diagnosed from symptoms and cycle changes; Canadian guidance is clear that no blood test is needed and that a “normal” result doesn’t rule it out, because levels swing day to day10. So the conversation starts with your symptoms, your age, your history, and what you want. Bring the result from our perimenopause check if you’ve done it. Ask about estradiol through the skin with micronized progesterone, since that’s the combination the evidence favours. Ask what’s covered, because in BC most of it now is. And if your clinician isn’t comfortable with any of this, ask for someone who is; we keep a list.
This article is general information, not medical advice. The medical professional who sees you in person may reach a different assessment, and their judgement takes precedence.