Amenorrhea is the medical term for the absence of menstrual periods. It’s not a disease on its own but a sign that something in the body has changed, whether that’s pregnancy, stress, significant weight loss, or an underlying hormonal condition. The term covers two distinct situations: never having had a period by a certain age, or losing periods after previously having them.
Primary vs. Secondary Amenorrhea
Primary amenorrhea means a person has never menstruated. It’s typically identified when someone hasn’t gotten their first period by age 15, despite otherwise normal growth and development. This can result from structural differences present from birth, genetic conditions, or hormonal issues that prevent puberty from progressing as expected.
Secondary amenorrhea is far more common. It means periods have stopped in someone who previously had them. The standard definition is missing periods for three or more consecutive cycle lengths if your cycles were previously regular, or for six or more months if your cycles were irregular. Pregnancy is the most obvious cause, but when pregnancy isn’t the explanation, something else is disrupting the hormonal chain reaction that drives menstruation.
How Your Cycle Gets Disrupted
Your menstrual cycle depends on a communication loop between three parts of the body: a region deep in the brain called the hypothalamus, the pituitary gland just below it, and the ovaries. The hypothalamus sends a signal that tells the pituitary to release hormones, which in turn tell the ovaries to mature an egg and produce estrogen. If any link in that chain is suppressed or interrupted, ovulation stalls and periods stop.
This is why so many different things can cause amenorrhea. A problem at the brain level (like chronic stress shutting down signals from the hypothalamus) produces the same end result as a problem at the ovary level (like PCOS interfering with egg maturation). The pathway is the same; the point of disruption differs.
The Three Most Common Triggers
Outside of pregnancy, the causes of secondary amenorrhea fall into a few well-established categories.
Low Energy Availability
When the body doesn’t have enough fuel to cover its basic needs, it shuts down functions that aren’t essential for survival, and reproduction is first on the list. This can happen through restrictive eating, rapid weight loss, or simply not eating enough to match a high activity level. The body reads the energy shortage as a signal that conditions aren’t safe for pregnancy, and the brain dials down the hormonal signals that drive the cycle.
There’s no single calorie threshold that triggers this response. Earlier research suggested that consuming fewer than 30 kilocalories per kilogram of lean body mass per day would reliably cause menstrual disruption, but more rigorous studies have not confirmed a clean cutoff. Some women lose their periods above that number, while others maintain normal cycles below it. Individual sensitivity varies, which makes this harder to predict than simple calorie math would suggest.
Psychological and Emotional Stress
Stress-related amenorrhea is sometimes described as a somatic response, meaning the body physically reacts to psychological pressure. The stressors involved range widely: major life upheaval, family conflict, fear for personal safety, grief, or even smaller transitions like starting a new school or job. What matters isn’t the objective severity of the event but how the person experiences it. Chronic stress elevates cortisol, which directly suppresses the brain’s reproductive signaling.
Excess Exercise
Intense training can contribute to amenorrhea through multiple pathways at once. High energy expenditure creates a calorie deficit even when someone is eating what seems like enough. Many athletes also restrict food intake to maintain a certain body composition. On top of that, the psychological pressure of competition and training goals adds its own stress. These factors overlap, which is why exercise-related amenorrhea is rarely about exercise alone.
PCOS and Hormonal Conditions
Polycystic ovary syndrome is one of the most common hormonal causes of irregular or absent periods. In PCOS, elevated levels of androgens (often called “male hormones,” though everyone produces them) interfere with the normal process of selecting and releasing a mature egg each month. Follicles begin developing but stall before ovulation, creating the characteristic cysts visible on ultrasound.
The hormonal environment in PCOS becomes self-reinforcing. High androgen levels recruit more follicles into early development while simultaneously preventing any single follicle from maturing fully. Meanwhile, insulin resistance, which is common in PCOS, further sensitizes the ovaries to signals that boost androgen production. The result is a noncyclic hormonal pattern that can persist without intervention.
Thyroid disorders and conditions affecting the pituitary gland can also cause amenorrhea by disrupting the same hormonal communication loop, though these are less common than PCOS.
Medications That Stop Periods
Certain medications can cause amenorrhea as a side effect. Hormonal contraceptives are the most familiar example, and periods often take a few months to return after stopping them. Antipsychotic medications are another significant category. Studies of women taking antipsychotics have found amenorrhea rates between 11 and 35%, with some medications carrying higher risk than others. Chemotherapy drugs, some antidepressants, and medications that affect hormone levels can also interrupt cycles.
Why It Matters for Bone Health
Amenorrhea isn’t just about missing periods. When the hormonal signals driving menstruation shut down, estrogen levels drop, and estrogen plays a critical role in maintaining bone density. The longer amenorrhea lasts, the more bone you can lose.
The numbers are striking. Roughly 44% of women with functional hypothalamic amenorrhea (the type caused by stress, low energy, or exercise) have low bone density. Between 10 and 25% have bone density scores in a range that’s essentially unheard of in healthy women of the same age, where fewer than 1% would score that low. Fracture risk in women with this type of amenorrhea is two to seven times higher than in their healthy peers.
This is especially concerning for younger women, because the late teens and twenties are when the skeleton is still building toward its peak bone mass. Missing that window means starting with a lower baseline, which increases the risk of osteoporosis later in life. Research tracking women with functional hypothalamic amenorrhea found that about 30% remain without periods after nine years, and delays in restoring normal cycles lead to progressively worse bone outcomes.
Beyond Bones: Other Health Effects
Low estrogen from chronic amenorrhea also affects cardiovascular health. Estrogen helps maintain healthy blood vessel function and favorable cholesterol levels, so prolonged deficiency can increase long-term heart disease risk. Fertility is an obvious concern as well: without ovulation, natural conception isn’t possible. Many women also report effects on mood, energy, sleep, and libido, all of which are influenced by the same hormones that regulate the menstrual cycle.
Getting Evaluated
The first step in evaluating amenorrhea is always ruling out pregnancy. After that, the workup typically involves blood tests to check levels of key hormones: thyroid function, the hormone that stimulates breast milk production (which can suppress periods when elevated), and markers of ovarian function. These results help pinpoint where in the hormonal chain the disruption is occurring.
For someone with secondary amenorrhea, the underlying cause determines the approach. If the issue is low energy availability, the path forward centers on restoring adequate nutrition and, if relevant, reducing exercise intensity. Stress-related amenorrhea often improves with psychological support and lifestyle changes. PCOS is managed differently, typically through strategies targeting insulin resistance and hormonal balance. In cases where bone loss is a concern and periods haven’t returned despite addressing root causes, hormone therapy may be considered to protect the skeleton and cardiovascular system.
The key point is that amenorrhea is always worth investigating. A missed period here and there may not signal a problem, but consistently absent periods indicate that the body’s hormonal environment has shifted in ways that can have real consequences for bones, heart health, fertility, and overall well-being.