Amenorrhea

What it is

Amenorrhea is the absence of menstrual periods, affecting an estimated 3–5% of reproductive-age women at any given time and ranking among the most common reasons for referral to a gynaecologist or endocrinologist. Also called absent menstruation, amenorrhea is not a diagnosis on its own but a symptom pointing to an underlying hormonal, structural, or systemic cause. Two clinical types exist: primary amenorrhea, defined as no first menstrual period by age 15 despite otherwise normal physical development, and secondary amenorrhea, defined as the cessation of previously regular periods for three or more consecutive cycles (or six or more months in someone with at least one prior spontaneous period). Pregnancy, breastfeeding, and menopause are normal, expected causes of absent periods and are excluded from the clinical definition. Left unaddressed, amenorrhea driven by low estrogen carries real risks for bone density, cardiovascular health, and fertility — making early evaluation important for Canadian patients regardless of whether the absence of periods feels bothersome.

Causes and mechanism

Normal menstruation depends on a coordinated hormonal chain: the hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary to release FSH and LH, which in turn drive ovarian follicle development, estrogen production, and ovulation. Disruption at any point in this axis — or in the uterine outflow tract — can produce amenorrhea.

Cause	Type most often seen	Key mechanism
Hypothalamic amenorrhea	Secondary	Stress, low body weight, or excessive exercise suppresses GnRH output
Polycystic ovary syndrome (PCOS)	Secondary	Elevated androgens and insulin resistance disrupt ovulation
Hyperprolactinemia	Secondary	Elevated prolactin (often from a benign prolactinoma) suppresses GnRH and FSH
Thyroid dysfunction	Either	Hypothyroidism or hyperthyroidism impairs hormonal signalling for ovulation
Primary ovarian insufficiency (POI)	Secondary	Ovaries cease normal function before age 40, depleting the follicle pool
Structural causes	Primary or secondary	Asherman's syndrome, imperforate hymen, or Müllerian abnormalities block outflow
Medications	Secondary	Hormonal contraceptives, antipsychotics, chemotherapy, some antidepressants

Hypothalamic amenorrhea is the most common cause of secondary amenorrhea in young women and is particularly prevalent among competitive athletes and people with restrictive eating patterns. Polycystic ovary syndrome (PCOS) — a condition characterized by elevated androgens, irregular ovulation, and often insulin resistance — is the most common endocrine disorder in reproductive-age women and a frequent driver of both irregular and absent cycles.

Symptoms and diagnosis

The defining feature is absent periods. Associated symptoms vary by cause and can include hot flashes and vaginal dryness (low estrogen from ovarian insufficiency or hypothalamic suppression), galactorrhoea or milky nipple discharge (elevated prolactin), excess facial or body hair and acne (elevated androgens, often PCOS), headaches or visual changes (possible pituitary tumour), and fatigue or weight changes (thyroid dysfunction).

Diagnostic workup typically follows this sequence:

1. Pregnancy test — always the first step; pregnancy is the most common cause of missed periods.
2. Hormone panel — FSH, LH, prolactin, TSH, and estradiol to map the hormonal cause.
3. Androgen levels — testosterone and DHEA-S if PCOS or hyperandrogenism is suspected.
4. Pelvic ultrasound — assesses ovarian morphology and uterine structure.
5. Brain MRI — ordered when prolactin is elevated or a pituitary tumour is suspected.
6. Karyotyping — considered in primary amenorrhea when a chromosomal cause such as Turner syndrome is possible.

In Canada, initial bloodwork is typically ordered through a family physician and processed at provincial labs (LifeLabs or Dynacare in most provinces). Referral to a gynaecologist or reproductive endocrinologist is appropriate when the cause is not identified on first-line testing or when fertility is a concern.

Treatment options

Treatment targets the underlying cause. Goals include restoring menstrual function where possible, correcting hormonal deficiencies, protecting bone density, and supporting fertility if desired.

• Hypothalamic amenorrhea: Restoring body weight, moderating exercise, and reducing psychological stress often resumes periods within months without medication. Cognitive behavioural therapy has demonstrated benefit in clinical trials.
• PCOS: Letrozole or clomiphene for ovulation induction when pregnancy is desired; combined oral contraceptives to regulate cycles and protect the endometrium; metformin to address insulin resistance.
• Hyperprolactinemia: Dopamine agonists — cabergoline or bromocriptine — lower prolactin effectively and frequently restore ovulation.
• Thyroid dysfunction: Treating hypothyroidism with levothyroxine typically normalizes cycles once thyroid levels stabilize.
• Primary ovarian insufficiency: Hormone replacement therapy (HRT) is recommended to replace estrogen, protect bone density, and support cardiovascular health. Fertility options include assisted reproduction with donor eggs.
• Structural causes: Surgical correction is required for conditions such as Asherman's syndrome or imperforate hymen.

For people not seeking pregnancy, progestogen therapy or combined oral contraceptives are often prescribed to induce regular withdrawal bleeding and protect the uterine lining from the effects of unopposed estrogen exposure.

When to see a clinician in Canada

Seek evaluation if you are over 15 and have not yet had a first period; if periods have been absent for three or more consecutive months and you are not pregnant; if cycles have stopped or become markedly irregular without an obvious explanation such as a recent contraceptive change; or if absent periods are accompanied by hot flashes, unexplained weight changes, excess hair growth, or nipple discharge. If you are trying to conceive, seek assessment after 12 months of trying (or 6 months if you are over 35). People with a history of an eating disorder, intense athletic training, or significant recent weight loss should seek support early, as hypothalamic amenorrhea responds well to timely intervention.

Canadian patients can access initial assessment through a family physician, nurse practitioner, or virtual care platforms (Felix, Maple, Cleo, Phoenix, and others operating in Canada). Specialist referral to a gynaecologist or reproductive endocrinologist is available through provincial health systems, though wait times vary by province.

Limitations and open questions

Research is still emerging on the optimal threshold for resuming periods in athletes with hypothalamic amenorrhea — specifically, how much weight restoration or exercise reduction is sufficient and over what timeline. The long-term cardiovascular consequences of amenorrhea in young women remain incompletely characterized, with most data extrapolated from postmenopausal estrogen-deficiency studies rather than premenopausal cohorts. Health Canada has not issued a standalone clinical guideline specific to amenorrhea management; Canadian clinicians generally follow the Endocrine Society's 2017 functional hypothalamic amenorrhea guideline and the Society of Obstetricians and Gynaecologists of Canada (SOGC) guidance on related conditions. The precise prevalence of each amenorrhea subtype within the Canadian population is not well documented in national surveillance data.