Hot flashes

What it is

Hot flashes affect more than 80% of people going through menopause, making them the most commonly reported symptom of the menopause transition. A hot flash — also called a hot flush or, clinically, a vasomotor symptom (VMS) — is a sudden, transient sensation of intense heat, typically spreading from the chest to the neck and face, accompanied by sweating, skin flushing, and sometimes palpitations or a feeling of anxiety. Individual episodes usually last 1 to 5 minutes. When they occur at night and disrupt sleep, they are called night sweats.

Hot flashes are not a brief inconvenience for most people. Data from the Study of Women's Health Across the Nation (SWAN) show that the median total duration of VMS is approximately 7.4 years, and for those who begin experiencing them before the final menstrual period, duration can exceed 11 years. In Canada, where the average age of natural menopause is 51, this means many people spend a substantial portion of their 50s managing moderate-to-severe VMS. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recognizes VMS as a primary indication for menopause hormone therapy (MHT) in appropriate candidates.

Causes and mechanism

Hot flashes arise from declining estrogen levels, which destabilize the hypothalamic thermoregulatory zone — the narrow temperature range within which the body neither sweats nor shivers. Research published in Menopause and elsewhere points to elevated hypothalamic norepinephrine activity and, more recently, to kisspeptin/neurokinin B/dynorphin (KNDy) neurons in the hypothalamic arcuate nucleus as the central drivers. As estrogen falls, KNDy neurons become hyperactive and trigger the thermoregulatory centre to misfire, producing a false "overheating" signal that sets off peripheral vasodilation and sweating.

Common triggers that narrow the thermoneutral zone further include:

• Warm ambient temperatures or hot beverages
• Alcohol and spicy foods
• Stress and anxiety
• Smoking (associated with earlier onset and greater severity)
• Higher body mass index (though evidence on direction of effect is mixed)

Hot flashes also occur in people who undergo surgical menopause (bilateral oophorectomy), in those receiving androgen-deprivation therapy for prostate cancer, and in breast cancer survivors on aromatase inhibitors or tamoxifen — contexts where estrogen drops abruptly rather than gradually.

Symptoms and diagnosis

Hot flashes are diagnosed clinically; no blood test confirms them. A clinician will typically assess:

Feature	Mild	Moderate	Severe
Frequency	< 7 per week	7–14 per week	> 14 per week
Sleep disruption	Rare	Occasional	Frequent / nightly
Daily function	Unaffected	Somewhat impaired	Significantly impaired
Duration of episode	< 1 min	1–3 min	> 3 min

Associated symptoms include heart palpitations, chills following the flush, irritability, and difficulty concentrating. Persistent or atypical presentations — such as hot flashes in someone well past menopause, or accompanied by weight loss and drenching sweats — warrant investigation to rule out secondary causes including thyroid dysfunction, carcinoid syndrome, lymphoma, or medication side effects. LifeLabs and Dynacare both offer FSH, estradiol, and TSH panels that Canadian clinicians commonly order to confirm menopausal status and exclude thyroid disease.

Treatment options

Hormone therapy remains the most effective treatment for VMS. Systemic estrogen (with progestogen for those with a uterus) reduces hot flash frequency by roughly 75% compared with placebo. The SOGC's 2021 Menopause: Consensus of Canadian Menopause Experts supports MHT as first-line therapy for healthy individuals under 60 or within 10 years of menopause onset who have bothersome VMS and no contraindications.

Non-hormonal prescription options include:

• Fezolinetant (Veozah) — a neurokinin B receptor antagonist approved by Health Canada in 2023; the first non-hormonal drug targeting the KNDy pathway directly. Reduces moderate-to-severe hot flash frequency by approximately 60% in trials.
• SSRIs/SNRIs — paroxetine (the only FDA-approved non-hormonal option in the US), escitalopram, and venlafaxine reduce frequency by 40–60%. Note: paroxetine is not recommended in women on tamoxifen due to CYP2D6 inhibition.
• Gabapentin — modestly effective, particularly for night sweats; sedation limits daytime use.
• Clonidine — modest benefit; side-effect profile limits use.

Lifestyle measures with some evidence include keeping rooms cool, layering clothing, reducing alcohol and caffeine, and cognitive behavioural therapy (CBT), which has RCT support for improving VMS-related quality of life even without reducing flash frequency.

Canadian patients can access MHT prescriptions through family physicians, gynaecologists, and menopause specialists, as well as through virtual care platforms such as Maple, Felix, Cleo, Phoenix, and others — though formulary coverage varies by province. In Ontario, for example, most oral and transdermal estrogen products are listed on the ODB formulary for eligible patients.

When to see a clinician in Canada

See a family physician, nurse practitioner, or gynaecologist if hot flashes are occurring more than 7 times per week, disrupting sleep on most nights, or affecting work or relationships. Seek care promptly if flashes are accompanied by unexplained weight loss, drenching sweats unrelated to ambient temperature, or new palpitations — these features warrant investigation beyond routine menopause management. The SOGC recommends that all people experiencing bothersome VMS be offered a discussion of both hormonal and non-hormonal options, with treatment individualized to personal health history and preference.

Limitations and open questions

Research is still emerging on why VMS duration varies so widely between individuals — from under a year to more than 14 years — and why Black women in the SWAN cohort experienced significantly longer and more severe VMS than white women, a disparity not yet fully explained by socioeconomic or hormonal factors. The long-term cardiovascular and cognitive effects of untreated severe VMS are an active area of study; some observational data link frequent night sweats to poorer sleep and higher cardiovascular risk, but causality has not been established. Health Canada has not yet issued specific guidance on compounded bioidentical hormone preparations for VMS, and evidence for their efficacy and safety relative to approved products remains limited. The role of phytoestrogens (soy isoflavones, red clover) is also uncertain — trial results are inconsistent, and no Canadian guideline currently recommends them as a primary treatment.