A missed period is most commonly caused by pregnancy, but dozens of other factors can delay or stop your cycle entirely. A single late period is rarely a sign of something serious. But if your previously regular periods have been absent for three months, or your irregular periods have been absent for six months, that crosses a clinical threshold called secondary amenorrhea, and it’s worth investigating.
Understanding what’s behind a missed period starts with ruling out the obvious, then working through the less obvious causes one by one.
Rule Out Pregnancy First
Pregnancy is the most common reason periods stop, so it’s the first thing to check. Home pregnancy tests detect a hormone called hCG, which your body starts producing about six days after fertilization. These tests are most reliable starting on the first day of your missed period. If you don’t track your cycle closely, take a test at least 21 days after you last had unprotected sex. Some highly sensitive tests can detect hCG even before a missed period, but waiting gives you a more accurate result.
If the test is negative and your period still hasn’t arrived after another week or two, take a second test. False negatives happen, especially if you tested too early.
Common Reasons Your Period Is Late
After pregnancy, the next most likely causes fall into a few broad categories: lifestyle factors, hormonal conditions, and medications.
Stress and body weight changes. Your brain’s hormonal signaling system is surprisingly sensitive to what’s happening in your life. Severe anxiety, emotional distress, sudden weight loss from extreme dieting or bariatric surgery, and very low body fat (below roughly 15 to 17 percent) can all shut down ovulation. So can intense, prolonged exercise. These causes fall under a category called functional hypothalamic amenorrhea, where the brain essentially decides conditions aren’t right for reproduction and dials back the hormones that drive your cycle.
Polycystic ovary syndrome (PCOS). PCOS is one of the most common hormonal disorders in women of reproductive age. Along with missed or irregular periods, it can cause excessive body hair, severe acne, insulin resistance that leads to weight gain, and dark, thick patches of skin. If you’re noticing several of these symptoms alongside irregular cycles, PCOS is a strong possibility.
Thyroid problems. An overactive thyroid gland can disrupt your menstrual cycle, as can an underactive one. Thyroid issues are common and treatable, which is why thyroid hormone levels are one of the first things checked during a workup for missed periods.
Hormonal birth control. If you’ve recently stopped taking birth control pills or injectable contraceptives, your periods may not return for more than six months. This is normal and doesn’t mean anything is wrong with your fertility long-term, but it can be unsettling if you’re not expecting it.
Breastfeeding. Nursing suppresses ovulation in many women, so missed periods during breastfeeding are common and expected. Cycles typically return once you reduce feeding frequency or stop entirely.
Less common causes. Certain medications, including some used for cancer treatment and psychiatric conditions, can stop periods. Pituitary gland tumors (usually small and benign) can overproduce a hormone called prolactin that interferes with your cycle. Scar tissue inside the uterus from procedures like a D&C or severe pelvic infections can also prevent menstrual bleeding, a condition known as Asherman syndrome. And premature ovarian insufficiency, where the ovaries stop functioning normally before age 40, is uncommon but possible.
What Your Age Has to Do With It
If you’re in your 40s, irregular or skipped periods may simply be the beginning of perimenopause, the transition leading up to menopause. Some women notice changes as early as their mid-30s, while others don’t until their 50s. During this phase, estrogen and progesterone levels rise and fall unpredictably rather than cycling smoothly. You might skip a month, have two periods close together, or experience heavier or lighter flow than usual.
Perimenopause typically lasts several years before periods stop for good. It’s a normal biological transition, but it’s still worth mentioning to your doctor, especially if symptoms like hot flashes, sleep disruption, or mood changes are affecting your daily life.
What Happens at the Doctor’s Office
If you’ve missed periods long enough to warrant a visit, the evaluation is straightforward. Your doctor will likely start with a pregnancy test (even if you’ve already taken one at home) and then order a panel of blood tests. These typically check thyroid-stimulating hormone to assess thyroid function, follicle-stimulating hormone to evaluate whether your ovaries are working normally, prolactin levels to screen for pituitary issues, and sometimes male hormone levels if you’re showing signs like increased facial hair or a deepening voice.
Depending on results, imaging like an ultrasound of your ovaries or an MRI of your pituitary gland may follow. The goal is to identify which part of the hormonal chain is misfiring, because that determines the treatment.
Why Prolonged Missed Periods Matter for Your Health
A missed period here and there isn’t dangerous on its own. But when periods stay absent for months or years, the real concern is what that signals about your estrogen levels. Estrogen does far more than drive your menstrual cycle. It plays a critical role in maintaining bone density, and prolonged deficiency can lead to significant bone loss.
This is especially concerning for younger women. Peak bone mass is established between ages 20 and 25, so missing periods during adolescence or early adulthood can create permanent deficits in bone density that increase fracture risk for the rest of your life. Research on women with hypothalamic amenorrhea, the type caused by low body weight or excessive exercise, shows fracture rates nearly double those of normal-weight peers: 43 percent in exercise-induced amenorrhea and 38 percent in anorexia nervosa, compared to 22 percent in controls.
Even after weight regain and the return of periods, bone density often remains lower than in women who never lost their cycles. Recovery tends to be incomplete because not all the hormonal disruptions fully normalize, and relapses are common.
Symptoms That Warrant a Prompt Call
Most causes of missed periods are manageable, but certain accompanying symptoms suggest you should get evaluated sooner rather than later. Pelvic pain combined with unusual bleeding or discharge alongside missed periods can be a symptom of endometrial cancer, where early detection makes a significant difference. Vision changes or persistent headaches with amenorrhea could point to a pituitary tumor pressing on nearby structures. And the cluster of symptoms associated with PCOS (rapid weight gain, severe acne, excessive hair growth) benefits from early treatment to prevent long-term metabolic complications like type 2 diabetes.
If your periods have been absent for three months and you’re not pregnant, breastfeeding, or on hormonal contraception, that’s a reasonable point to schedule an appointment. The workup is simple, the causes are almost always treatable, and catching hormonal imbalances early protects your bones, metabolism, and fertility down the line.