Pregnancy is the most common reason for a missed period, but it’s far from the only one. Stress, weight changes, hormonal conditions, medications, and even normal aging can all delay or stop your cycle. A period is generally considered late if your cycle stretches beyond 35 days, and if you go three months without one (and you’re not pregnant), something worth investigating is going on.
Pregnancy: The First Thing to Rule Out
If there’s any chance you could be pregnant, a home test is the fastest way to get an answer. Most standard home pregnancy tests detect the pregnancy hormone at concentrations of 20 to 25 mIU/mL, which is typically enough to show a positive result around the day of your missed period. Early-detection tests can pick up levels as low as 10 mIU/mL, meaning they may work a few days sooner. A blood test at a doctor’s office is even more sensitive, detecting levels as low as 1 to 5 mIU/mL.
If your test is negative but your period still hasn’t arrived a week later, test again. Sometimes hormone levels just aren’t high enough yet, especially if you ovulated later than usual that cycle.
Stress and Your Hormones
When you’re under significant stress, whether emotional, physical, or psychological, your body ramps up production of cortisol. Cortisol directly interferes with the hormonal chain that triggers ovulation. Specifically, it suppresses the brain signals that tell your ovaries to release an egg. No ovulation means no period, or at least a significantly delayed one.
This isn’t limited to extreme trauma. A demanding stretch at work, a family crisis, poor sleep over several weeks, or even the stress of moving to a new city can be enough. The effect is usually temporary: once the stressor resolves, cycles typically return within one to three months. But chronic, ongoing stress can keep periods absent for much longer.
Low Body Weight and Undereating
Your body needs a minimum amount of energy and body fat to sustain a menstrual cycle. Research shows that a body fat percentage below about 17 to 22 percent can cause periods to stop, a condition called functional hypothalamic amenorrhea. One study found that a body fat percentage of around 21% was the threshold most strongly associated with periods returning in people who had lost them.
This is common among athletes, people with eating disorders, and anyone who has cut calories drastically. The key metric isn’t just weight but energy availability: when your body is getting fewer than about 30 calories per kilogram of fat-free mass per day, it starts shutting down non-essential functions, and reproduction is one of the first to go. Your brain essentially reads the situation as “not enough resources to support a pregnancy” and turns off the hormonal signals that drive your cycle.
Recovery involves eating more. For many people, increasing caloric intake and reaching that energy threshold is enough to restart periods, though it can take several months.
Polycystic Ovary Syndrome (PCOS)
PCOS is one of the most common hormonal conditions in women of reproductive age, and irregular or missing periods are a hallmark. The condition involves higher-than-normal levels of androgens (often called “male hormones,” though everyone produces them). These elevated androgens interfere with ovulation, so eggs aren’t released on a regular schedule.
Beyond missed periods, signs of PCOS include persistent acne, thinning hair on the scalp, excess hair growth on the face or body, and difficulty losing weight. Diagnosis typically requires at least two of three findings: signs of high androgens, irregular ovulation, and a characteristic appearance of the ovaries on ultrasound. A blood ratio of two specific pituitary hormones (LH to FSH) greater than 2 is another indicator, though no single test is definitive on its own.
PCOS doesn’t go away, but it’s very manageable. Treatment usually focuses on regulating cycles through hormonal contraceptives, managing symptoms like acne or hair growth, and addressing insulin resistance if it’s present.
Thyroid Problems
Both an underactive and overactive thyroid can disrupt your period, but hypothyroidism (underactive) is the more common culprit for missed periods. When your thyroid isn’t producing enough hormone, your pituitary gland works harder to stimulate it. That increased activity also raises prolactin, a hormone normally associated with breastfeeding. Elevated prolactin suppresses the signals that drive ovulation, leading to infrequent or absent periods.
Other signs of an underactive thyroid include fatigue, weight gain, feeling cold, dry skin, and brain fog. A simple blood test can check your thyroid levels, and treatment with thyroid hormone replacement typically restores normal cycles.
Medications That Affect Your Cycle
Several types of medications can cause missed periods, most commonly by raising prolactin levels.
- Antipsychotic medications are the most frequent offenders. Nearly all of them can increase prolactin, and some do so at even low doses. The effect is generally dose-dependent.
- Antidepressants, particularly SSRIs, can also raise prolactin by boosting serotonin levels. This side effect has been documented across multiple types, including both newer and older antidepressants.
- Anti-nausea medications that block dopamine work through a similar mechanism.
Women taking these medications commonly experience infrequent or absent periods, along with other symptoms of high prolactin like breast tenderness or unexpected milk production. If you suspect a medication is affecting your cycle, your prescriber can check your prolactin level and potentially adjust your treatment.
Hormonal Contraceptives
Some forms of birth control are designed to lighten or eliminate periods, and missing your period while using them is expected rather than concerning. Hormonal IUDs thin the uterine lining so much that roughly half of users experience very light or absent periods by two years of use. The hormonal implant and the shot can have similar effects.
Even after stopping hormonal birth control, it can take a few months for your cycle to regulate. This is particularly common after the injection, where it may take six months or longer for periods to return. Coming off the pill, most people see their period return within one to three months.
Perimenopause
If you’re in your 40s (or occasionally your late 30s) and your periods are becoming unpredictable, perimenopause is a likely explanation. This transition phase leading up to menopause can last several years.
An early sign is a shift of seven or more days in your cycle length from what’s been normal for you. So if your cycle has always been 28 days and it’s now regularly 36 or 37, that’s a meaningful change. In late perimenopause, gaps of 60 days or more between periods are common. You may also notice heavier or lighter flow, hot flashes, sleep disruption, and mood changes. Menopause is officially reached after 12 consecutive months without a period.
Other Less Common Causes
A few additional factors can cause missed periods. Excessive exercise, even without significant weight loss, can suppress ovulation through the same stress-hormone pathway described above. Endurance athletes, dancers, and gymnasts are particularly vulnerable. Breastfeeding suppresses ovulation in many women, especially in the first six months postpartum when nursing frequently. Chronic illnesses like uncontrolled diabetes or celiac disease can disrupt cycles by affecting overall hormonal balance. And in rare cases, structural problems like scarring inside the uterus (sometimes after a procedure like a D&C) can prevent normal shedding of the uterine lining.
If you’ve missed three consecutive periods and pregnancy isn’t the explanation, that’s the standard threshold at which a full diagnostic workup is recommended. This typically involves blood tests to check thyroid function, prolactin, and reproductive hormone levels, along with an ultrasound in some cases. Most causes of missed periods are treatable once identified.