A missed period has many possible explanations, and pregnancy is only one of them. About 1 in 4 women who aren’t pregnant, breastfeeding, or going through menopause will miss a period at some point in their lives. The cause can range from something temporary like stress or a new medication to an underlying hormonal condition that needs attention.
Rule Out Pregnancy First
If there’s any chance you could be pregnant, a home test is the fastest way to get clarity. Pregnancy tests are most reliable starting on the first day of your missed period. If your cycle is irregular and you’re not sure when your period was due, take a test at least 21 days after you last had unprotected sex. All home tests detect the same hormone (hCG), which your body starts producing about six days after fertilization. A negative result on the day of your missed period is fairly reliable, but if you test earlier than that, a negative result is less trustworthy and worth repeating a few days later.
Stress and Your Cycle
Your menstrual cycle is controlled by a chain of hormone signals that starts in your brain. When you’re under significant physical or emotional stress, your brain can dial down or delay the hormone surge that triggers ovulation. No ovulation means no period, or a late one. This doesn’t require a major life crisis. A bad stretch at work, poor sleep for a few weeks, grief, or even travel across time zones can be enough to push your cycle off track. Once the stress resolves, your period typically returns on its own within a cycle or two.
Undereating and Overexercising
Your body needs a minimum amount of energy to maintain a regular cycle. When you’re not eating enough to support your activity level, your brain interprets that energy deficit as a signal to shut down reproduction. This is common in athletes, but it also happens to anyone who drastically cuts calories, develops disordered eating patterns, or rapidly loses weight.
There’s no single calorie threshold that applies to everyone. Research has found significant individual variability in how much of an energy deficit it takes to disrupt someone’s cycle. Some people lose their period after a modest increase in exercise; others maintain regular cycles through intense training. The key factor is whether your body has enough fuel left over after exercise and daily activity to run its normal hormonal processes. If your period disappears alongside increased exercise or reduced food intake, that’s a clear signal your body is running on too little energy, and it has consequences beyond your cycle, including bone density loss over time.
Birth Control and Medications
Certain types of hormonal birth control are designed to thin the uterine lining so much that you have very light periods or none at all. Hormonal IUDs, the injectable contraceptive (Depo-Provera), and some continuous-use birth control pills all commonly cause missed periods. This is an expected side effect, not a sign that something is wrong. If you recently started or stopped hormonal contraception, it can take several months for your natural cycle to regulate.
A surprisingly wide range of other medications can also stop your period. Antipsychotics, certain antidepressants (including SSRIs and tricyclics), opioid pain medications, anti-seizure drugs, and even some blood pressure medications can interfere with the hormones that drive your cycle. Many of these work by raising levels of prolactin, a hormone that suppresses ovulation. If your period disappeared around the same time you started a new medication, that connection is worth raising with whoever prescribed it.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in women of reproductive age, and irregular or missing periods are its hallmark symptom. In PCOS, the ovaries produce higher-than-normal levels of androgens (sometimes called “male hormones,” though everyone has them). This hormonal imbalance can prevent eggs from maturing and being released on a regular schedule, so periods become unpredictable or stop altogether.
Other signs that point toward PCOS include acne that persists well past your teenage years, excess hair growth on the face or body, thinning hair on your head, and difficulty losing weight. Not everyone with PCOS has all of these symptoms. A diagnosis typically involves blood work to check hormone levels and sometimes an ultrasound. PCOS is very manageable once identified, and treatment depends on whether your main concern is regulating your cycle, managing symptoms like acne, or trying to conceive.
Thyroid Problems
Your thyroid gland sets the pace for almost every process in your body, including your menstrual cycle. Both an underactive thyroid (hypothyroidism) and an overactive one (hyperthyroidism) can cause missed or irregular periods. An underactive thyroid is the more common culprit. When your thyroid slows down, it triggers a rise in prolactin, the same hormone that suppresses ovulation during breastfeeding. The result is the same: no ovulation, no period.
Other clues that your thyroid might be involved include unexplained fatigue, weight changes that don’t match your habits, feeling unusually cold or warm, hair thinning, and brain fog. A simple blood test can check your thyroid function, and treatment with thyroid hormone replacement typically restores a normal cycle.
Perimenopause
If you’re in your 40s (or sometimes your late 30s), a missed period could be an early sign of perimenopause, the transitional phase before menopause. Perimenopause usually starts in your mid-40s but can begin as early as your mid-30s or as late as your mid-50s. It lasts an average of eight to ten years before your periods stop permanently.
During this phase, your estrogen levels fluctuate unpredictably rather than declining in a straight line. That means your cycles may get shorter or longer, your flow heavier or lighter, and you might skip periods entirely for a month or two before they return. Other common signs include hot flashes, sleep disruption, mood changes, and vaginal dryness. If you’re under 40 and suspect this is happening, it’s worth getting checked, since premature ovarian insufficiency (early menopause) can affect bone health and fertility and benefits from early treatment.
Other Medical Causes
A few less common conditions can also explain a missing period. Scarring inside the uterus, sometimes called Asherman syndrome, can develop after a surgical procedure like a D&C and physically prevent the uterine lining from building up normally. Chronic illnesses like uncontrolled diabetes or celiac disease can disrupt your cycle by putting your body under sustained metabolic stress. And small, benign tumors on the pituitary gland (a structure in your brain that orchestrates hormone production) can overproduce prolactin and shut down ovulation.
When a Missed Period Needs Medical Attention
A single late or skipped period after an obviously stressful month is common and usually resolves on its own. The NHS recommends seeing a doctor if you’ve missed three periods in a row. You should also get evaluated sooner if your missed period comes with symptoms like persistent pelvic pain, unusual discharge, sudden weight changes, new hair growth on your face or chest, or milky discharge from your nipples when you’re not breastfeeding. These patterns help point toward a specific cause, and most of them are straightforward to diagnose with blood work and, in some cases, an ultrasound.