Missed periods can result from dozens of different causes, ranging from pregnancy and stress to hormonal conditions and certain medications. If you’ve missed three or more periods in a row without an obvious explanation, that’s generally the threshold where an evaluation is warranted. But understanding the most common causes can help you figure out what might be going on and whether you need to act.
Pregnancy Is the Most Common Cause
The single most common reason for a missed period in someone who menstruates is pregnancy. Even if you use birth control, no method is 100% effective. A home pregnancy test is the fastest way to rule this out, and most tests are accurate by the first day of a missed period. If pregnancy isn’t the cause, the list of possibilities opens up considerably.
Stress and Your Hormonal Signals
Your brain controls your menstrual cycle through a chain of hormonal signals that starts in a small region called the hypothalamus. Stress disrupts this chain directly. When you’re under significant physical or emotional stress, your body releases compounds that suppress the hormonal signal responsible for triggering ovulation. Without ovulation, your period doesn’t arrive on schedule.
This isn’t limited to dramatic life events. Ongoing work pressure, sleep deprivation, grief, or anxiety can all be enough to delay or skip a period. The effect is usually temporary. Once the stress resolves, your cycle typically returns within one to three months.
Low Body Weight and Excessive Exercise
Your body needs a minimum level of energy intake to maintain a menstrual cycle. When energy availability drops below about 30 calories per kilogram of body weight per day, physiological changes begin that can shut down ovulation. This can happen through restrictive eating, excessive exercise, or a combination of both.
Among female athletes, menstrual irregularities are strikingly common. A review of 65 studies found that the prevalence of at least one component of the “female athlete triad” (low energy availability, menstrual dysfunction, and bone loss) ranged from 16% to 60% in exercising women. But you don’t need to be an elite athlete for this to apply. Rapid weight loss from any cause, including illness or dieting, can have the same effect. In animal studies, reducing dietary intake by more than 30% resulted in infertility.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal disorders in women of reproductive age, and irregular or missed periods are a hallmark feature. In PCOS, the ovaries produce higher-than-normal levels of androgens (hormones typically associated with male development), which can prevent eggs from maturing and being released on a regular schedule.
Signs that PCOS might be behind your missed periods include excess facial or body hair, acne that persists past your teens, and difficulty losing weight. Excess body hair alone is considered predictive of the condition in adults. Diagnosis typically involves blood tests to check hormone levels and sometimes an ultrasound to look at the ovaries, where a high number of small follicles (20 or more in at least one ovary) is a key marker.
Thyroid Problems
Both an underactive thyroid (hypothyroidism) and an overactive thyroid can throw off your cycle. Your thyroid gland regulates metabolism throughout your body, and when it isn’t producing the right amount of hormones, the ripple effects reach your reproductive system. An underactive thyroid can also raise levels of prolactin, a hormone that further suppresses the signals needed for ovulation. Thyroid disorders are straightforward to detect with a blood test and are highly treatable.
High Prolactin Levels
Prolactin is the hormone responsible for milk production after childbirth, which is why breastfeeding commonly delays the return of periods. But prolactin can become elevated outside of pregnancy and breastfeeding for several reasons, and when it does, it disrupts your cycle.
A small, noncancerous tumor on the pituitary gland (called a prolactinoma) is one well-known cause. But other conditions can raise prolactin too, including hypothyroidism, chronic kidney or liver disease, Cushing disease, and even chest wall injuries like fractured ribs. PCOS itself is also associated with elevated prolactin in some cases.
Medications That Can Stop Periods
A surprisingly wide range of medications can cause missed periods, often by raising prolactin levels or shifting your hormonal balance. The major categories include:
- Antipsychotics like risperidone, haloperidol, and olanzapine
- Antidepressants, including SSRIs and tricyclic antidepressants
- Opioid pain medications such as codeine and morphine
- Blood pressure medications like methyldopa and verapamil
- Anti-nausea medications and drugs used for acid reflux
- Anti-seizure medications such as valproate and carbamazepine
- Anabolic steroids and testosterone
If your periods became irregular or stopped after starting a new medication, that connection is worth discussing with whoever prescribed it. In many cases, an alternative medication can be used.
Hormonal Birth Control and Its Aftermath
Many forms of hormonal birth control intentionally lighten or eliminate periods. Hormonal IUDs, certain pills taken continuously, and long-acting injections can all cause periods to stop entirely while you’re using them. This is a known, expected effect and not a sign of a problem.
After stopping hormonal birth control, most people see their period return fairly quickly. In one large study, 89% of women began menstruating within 60 days of stopping oral contraceptives. Only 7% took 180 days or longer. In rare cases (about 2.2% of users), the delay stretched further, with the longest recorded gap being 540 days. All women in the study did eventually resume menstruating on their own.
Perimenopause
If you’re in your 40s and noticing your periods becoming unpredictable, perimenopause is a likely explanation. This transitional phase before menopause typically begins in the 40s, though some women notice changes as early as their 30s or as late as their 50s.
In early perimenopause, your cycle length may vary by seven days or more from month to month. As you progress into late perimenopause, gaps of 60 days or more between periods are common. This phase can last several years before periods stop entirely. Menopause is officially defined as 12 consecutive months without a period.
Less Common but Worth Knowing
A few other conditions can cause missed periods, though they’re less frequent. Structural issues like scarring inside the uterus (often from a prior surgical procedure) can prevent the uterine lining from building up normally. Problems with the pituitary gland or adrenal glands can disrupt the hormonal chain at various points. Premature ovarian insufficiency, where the ovaries stop functioning normally before age 40, affects roughly 1% of women and causes periods to become irregular or stop.
Significant weight gain can also affect your cycle, as excess fat tissue produces estrogen that can interfere with normal ovulation patterns. Chronic illnesses, including celiac disease and diabetes, sometimes contribute as well.
How Many Missed Periods Matter
An occasional late or skipped period, especially during times of stress or illness, is normal and not usually a sign of something serious. The general guideline is that three or more consecutive missed periods warrants evaluation, regardless of your age. For teens who haven’t started menstruating by age 15, or who show no signs of breast development by age 13, earlier evaluation is appropriate.
The evaluation itself is typically straightforward: a pregnancy test, blood work to check hormone levels (including thyroid function and prolactin), and sometimes an ultrasound. In most cases, the cause is identifiable and treatable.