A missed period has many possible causes beyond pregnancy. Stress, body weight changes, hormonal conditions, thyroid problems, and certain medications can all delay or stop menstruation. If your previously regular periods have stopped for three months, or irregular periods have stopped for six months, that’s considered secondary amenorrhea and worth investigating.
Stress and Your Reproductive Hormones
Psychological stress is one of the most common reasons for a missed period, and the mechanism is surprisingly direct. When you’re under chronic stress, your body produces elevated levels of cortisol. Cortisol acts on a cluster of specialized neurons in the brain that normally stimulate the hormonal cascade responsible for ovulation. Specifically, cortisol suppresses kisspeptin, a signaling molecule that triggers the release of gonadotropin-releasing hormone (GnRH). Without normal GnRH pulses, your pituitary gland doesn’t release enough of the hormones that tell your ovaries to mature and release an egg. No ovulation, no period.
This isn’t just about feeling anxious. Major life disruptions, grief, work burnout, relationship crises, and even prolonged sleep deprivation can raise cortisol enough to interfere with your cycle. The effect is often temporary. Once the stressor resolves or you develop better coping strategies, cycles typically resume within a few months.
Low Body Weight and Undereating
Your body needs a minimum amount of energy to sustain a menstrual cycle, and when it doesn’t get enough, reproduction is one of the first systems to shut down. This condition, called functional hypothalamic amenorrhea (FHA), follows the same basic pathway as stress: your brain reduces GnRH output, and ovulation stops.
The threshold is measurable. Physicians use a metric called energy availability, which accounts for how many calories you have left after exercise. Below 30 calories per kilogram of fat-free mass per day, your body enters a conservation mode where many physiological systems start to malfunction, including your menstrual cycle. A range of 30 to 45 calories per kilogram of fat-free mass is considered reduced and only safe for short periods. Normal energy balance sits at 45 or above.
This affects athletes, people with eating disorders, and anyone who is dieting aggressively or combining heavy exercise with insufficient food intake. Recovery often requires gaining weight. Research shows that each additional kilogram of body fat increases the likelihood of menstruation returning by about 8%, and a body fat percentage above 22% may be needed to fully restore regular cycles. That number surprises many people, since it’s higher than the “lean” aesthetic often promoted in fitness culture.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal disorders in women, affecting 5 to 10 percent of women depending on the population studied. It’s characterized by irregular or absent periods, elevated levels of androgens (male-type hormones), and often the presence of multiple small follicles on the ovaries visible on ultrasound.
The typical menstrual pattern with PCOS is oligomenorrhea, meaning fewer than nine periods per year. Some women experience complete absence of periods for three or more consecutive months. The hormonal imbalance prevents the normal maturation and release of eggs, so cycles become unpredictable or stop altogether.
PCOS frequently comes with other metabolic features: insulin resistance, weight gain (particularly around the midsection), acne, excess facial or body hair, and thinning hair on the scalp. It also increases long-term risk for type 2 diabetes, cardiovascular disease, and fatty liver. Diagnosis typically follows the Rotterdam criteria, which require at least two of three features: irregular periods, signs of androgen excess, and polycystic ovaries on imaging. If your periods have always been irregular and you notice any of these other signs, PCOS is a likely explanation.
Thyroid Disorders
Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can disrupt your cycle, though they do so through slightly different routes.
With hypothyroidism, low thyroid hormone levels trigger a chain reaction. Your brain increases production of a hormone called TRH, which in turn stimulates prolactin release. Prolactin, the same hormone that drives milk production during breastfeeding, directly suppresses GnRH neurons and reduces kisspeptin expression. The result is lower levels of the hormones that drive ovulation (LH and FSH), leading to missed or absent periods. Studies in hypothyroid women have confirmed that LH and FSH are suppressed and increase again once thyroid levels return to normal.
Hyperthyroidism affects the cycle differently. Excess thyroid hormones increase levels of a protein called sex hormone-binding globulin, which binds to estrogen and other sex hormones in the blood and reduces their availability. Women with hyperthyroidism have a higher prevalence of menstrual irregularities and anovulatory cycles, though the precise mechanisms are less well understood than with hypothyroidism.
Thyroid conditions are common and treatable, and a simple blood test can identify them. If your missed periods come with fatigue, weight changes, feeling unusually cold or hot, or changes in heart rate, a thyroid issue is worth ruling out.
High Prolactin Levels
Hyperprolactinemia, or abnormally high prolactin, is the most common cause of anovulation driven by hormonal suppression and a leading cause of infertility in women aged 25 to 34. Prolactin suppresses the release of GnRH by acting on kisspeptin neurons in the brain. Without adequate GnRH, your pituitary produces less LH and FSH, and ovulation doesn’t occur.
The most common cause of high prolactin is a small, benign pituitary tumor called a prolactinoma. Most prolactinomas in women are microadenomas (smaller than 10 millimeters) and typically cause amenorrhea, sometimes accompanied by galactorrhea (unexpected breast milk production). These tumors respond well to medication in the vast majority of cases. High prolactin can also result from medications (more on that below), hypothyroidism, or other pituitary conditions.
Medications That Can Stop Your Period
Several classes of medication can cause missed periods, often by raising prolactin levels. The mechanism for many of these drugs involves blocking dopamine receptors in the pituitary gland. Dopamine normally keeps prolactin in check, so when it’s blocked, prolactin rises and suppresses ovulation.
Medications linked to this effect include:
- Antipsychotics (both older and newer generations), which are among the most common culprits
- Some antidepressants, including tricyclics, MAO inhibitors, and certain SSRIs
- Anti-nausea medications like metoclopramide and domperidone
- Opioid pain medications
- Certain blood pressure medications
A separate group of medications can raise androgen levels, which also disrupts ovulation. These include anabolic steroids, testosterone supplements, high-dose androgenic progestins, and some anti-seizure drugs like valproate and carbamazepine. Hormonal contraceptives deserve their own mention: some methods, especially hormonal IUDs, implants, and injectable contraceptives, are designed to thin the uterine lining and can cause very light or absent periods. This is a normal and expected effect, not a sign of a problem.
If your periods stopped shortly after starting a new medication, that connection is worth discussing with your prescriber. In many cases, an alternative medication can restore normal cycles.
Primary Ovarian Insufficiency
Primary ovarian insufficiency (sometimes called premature ovarian failure) occurs when the ovaries stop functioning normally before age 40. It’s less common than the other causes on this list but important to recognize because it has implications for bone health, cardiovascular risk, and fertility.
The hallmark is elevated FSH levels in the menopausal range, typically above 30 to 40 mIU/mL on two separate blood tests taken a month apart. Risk factors include a family history of early menopause, autoimmune disorders, prior chemotherapy, and pelvic radiation. Symptoms often resemble perimenopause: irregular or absent periods, hot flashes, vaginal dryness, and difficulty sleeping. Unlike natural menopause, primary ovarian insufficiency can occasionally be intermittent, with some women experiencing spontaneous ovulation even after diagnosis.
Excessive Exercise
Intense physical training can stop periods even when weight loss isn’t dramatic. The issue is the same energy deficit described earlier: if your exercise output exceeds your calorie intake by enough to drop energy availability below 30 calories per kilogram of fat-free mass per day, your hypothalamus dials down reproductive function. This is particularly common in endurance athletes, gymnasts, dancers, and anyone training at high volumes without proportionally increasing their food intake.
The fix isn’t necessarily exercising less. It’s eating more. Many athletes can maintain their training load and restore their cycles by increasing calorie intake, particularly carbohydrates and fats. Ignoring exercise-related amenorrhea carries real consequences: prolonged estrogen deficiency weakens bones, and stress fractures become significantly more likely.
Other Causes Worth Knowing
A few less common causes round out the picture. Uterine scarring from procedures like dilation and curettage (D&C) can physically prevent the uterine lining from building up and shedding, a condition called Asherman syndrome. Chronic illnesses like uncontrolled diabetes or celiac disease can disrupt hormonal balance enough to affect the cycle. Significant rapid weight gain can also throw off hormonal signaling, particularly if it contributes to insulin resistance.
Perimenopause, the transition leading up to menopause, typically begins in the mid-40s but can start earlier. Irregular and skipped periods are often the first sign, sometimes years before periods stop entirely. If you’re in your early to mid-40s and noticing cycles becoming unpredictable, this natural transition is a likely explanation.