A missed period has many possible causes beyond pregnancy. Stress, hormonal conditions, weight changes, medications, and the natural transition toward menopause can all disrupt your cycle. A period is considered late when it’s 5 or more days past your expected date, and officially “missed” when you go more than 6 weeks without menstrual flow.
Understanding the most common reasons can help you figure out what’s going on and whether it needs attention.
Pregnancy
The most obvious cause is worth ruling out first. If you’re sexually active and your period is late, a home pregnancy test is reliable from the first day of your missed period. Testing too early can produce a false negative, so if the result is negative but your period still doesn’t arrive, test again a week later.
Stress and Its Effect on Hormones
Your brain is the starting point of your menstrual cycle. A region in the brain sends out a hormone signal that eventually tells your ovaries to release an egg. When you’re under significant stress, your body produces more cortisol, and cortisol directly interferes with that signaling chain. It suppresses the release of the triggering hormone and also reduces the activity of another key chemical messenger (kisspeptin) that helps get the process started. The result: your brain essentially tells your reproductive system to stand down.
This isn’t limited to emotional stress. Physical stress from illness, surgery, travel across time zones, or sleep deprivation can have the same effect. The missed period typically resolves once the stressor passes, but prolonged stress can cause cycles to disappear for months. Clinicians call this functional hypothalamic amenorrhea, and it’s one of the most common explanations for unexplained missed periods in otherwise healthy women.
Low Body Weight and Caloric Deficit
Women with very low body fat are at high risk for losing their periods. The connection comes down to a hormone called leptin, which is produced by fat cells. Leptin acts as a messenger between your metabolism and your reproductive system, essentially telling your brain whether your body has enough energy reserves to support a pregnancy. When body fat drops too low, leptin levels fall, and your brain stops sending the signals needed for ovulation.
What’s particularly striking is that a caloric deficit alone, even without significant fat loss, can trigger this cascade. Energy deprivation has a rapid effect on lowering leptin levels, which is why athletes, people with eating disorders, and those on extreme diets can lose their periods while still at a relatively normal weight. In one study, women who had lost their periods had an average body fat of about 21.5%, compared to 25% in women with normal cycles, and their leptin levels were significantly lower even after accounting for the difference in body fat.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in women of reproductive age and a leading cause of irregular or missed periods. It involves elevated levels of androgens (sometimes called “male hormones,” though everyone produces them). These excess androgens interfere with the normal process of ovulation, meaning eggs aren’t released on a regular schedule, and periods become unpredictable or absent.
One theory for what drives PCOS centers on insulin resistance. When your body doesn’t respond well to insulin, it compensates by producing more, and high insulin levels increase androgen production from both the ovaries and the adrenal glands. The condition is diagnosed when at least two of three features are present: signs of high androgens (such as acne, excess facial or body hair, or thinning hair on the scalp), irregular ovulation, and ovaries with a characteristic appearance on ultrasound. If you’re missing periods and also noticing skin or hair changes, PCOS is worth discussing with your doctor.
Thyroid Problems
Both an overactive and an underactive thyroid can disrupt your cycle. Thyroid hormones influence the balance of reproductive hormones, and when they’re off, ovulation becomes unreliable. Your periods may become heavier, lighter, irregular, or stop entirely.
An underactive thyroid has a specific additional mechanism: it can cause your body to overproduce prolactin, the same hormone responsible for milk production during breastfeeding. Excess prolactin suppresses ovulation. A simple blood test can check your thyroid function, and treatment with thyroid medication typically restores normal cycles.
High Prolactin Levels
Even outside of thyroid problems, elevated prolactin is a well-recognized cause of missed periods. High prolactin disrupts the normal pulsing of hormonal signals from the brain, leading to inadequate stimulation of the ovaries. Follicles don’t mature properly, ovulation doesn’t occur, and periods stop.
The most common medical cause of high prolactin is a small, benign growth on the pituitary gland called a prolactinoma. These are usually treatable with medication. But prolactin can also be raised by a surprisingly long list of drugs and substances, which brings us to the next cause.
Medications and Substances
Several classes of medication can cause missed periods, often by raising prolactin levels or by altering androgen levels. The most commonly implicated include:
- Antipsychotics (both older and newer types), which block dopamine receptors in the pituitary gland and allow prolactin to rise unchecked
- Some antidepressants, including certain SSRIs and older tricyclic antidepressants
- Opioids, which can suppress reproductive hormones with regular use
- Anti-seizure medications like valproate and carbamazepine, which can increase androgen levels
- Certain blood pressure medications and gastrointestinal drugs like metoclopramide
- Anabolic steroids and testosterone supplements
- Cocaine
If your periods became irregular after starting a new medication, that connection is worth raising with your prescriber. Stopping or switching the drug often restores normal cycles, but never change a medication without medical guidance.
Hormonal Birth Control
Hormonal contraceptives are designed to alter your cycle, and some are very effective at eliminating periods altogether. About half of women using a hormonal IUD experience absent or very infrequent periods by two years of use. The implant and progestin-only pills can have a similar effect.
This is generally considered a harmless side effect, not a sign that something is wrong. If you’ve recently stopped hormonal birth control, it can also take a few months for your natural cycle to resume. The delay varies by method but is usually resolved within three to six months.
Perimenopause
The transition to menopause doesn’t happen overnight. Perimenopause typically starts in your mid-40s, though it can begin as early as your mid-30s or as late as your mid-50s. During this phase, hormone levels rise and fall erratically rather than declining in a smooth, predictable way. Your ovaries may release an egg one month and skip the next, leading to cycles that are shorter, longer, heavier, lighter, or entirely absent for stretches of time.
Blood tests measuring FSH (the hormone that stimulates ovulation) can offer clues, but they’re not definitive during perimenopause because hormone levels fluctuate so much from week to week. A consistently elevated FSH level suggests you’re approaching menopause, but a single normal reading doesn’t rule it out. Perimenopause lasts an average of four to eight years before periods stop permanently.
Other Medical Causes
Less common but worth knowing about: structural issues like scarring inside the uterus (sometimes caused by a previous surgical procedure), premature ovarian insufficiency (when the ovaries stop functioning before age 40), and chronic illnesses that place ongoing metabolic stress on the body can all cause missed periods. Significant recent weight gain can also disrupt hormonal balance, partly through the same insulin-resistance pathway seen in PCOS.
How Many Missed Periods Should Prompt a Visit
The American College of Obstetricians and Gynecologists recommends evaluation if your period stops for more than 3 months without a clear explanation. That said, even a single missed period is worth investigating if you’re also experiencing new symptoms like unusual hair growth, significant weight changes, milky discharge from the nipples, hot flashes, or persistent fatigue. These patterns can point your doctor toward the right tests, which typically start with a pregnancy test, bloodwork for thyroid function and prolactin, and sometimes an ultrasound of the ovaries.