A period lasting a full month is not normal, and it signals that something in your body needs attention. A typical menstrual period lasts between two and seven days. Anything beyond seven days is classified as prolonged bleeding, and a period stretching to a month points to an underlying cause that can usually be identified and treated.
What Counts as Abnormally Long Bleeding
The CDC defines heavy menstrual bleeding as any period lasting more than seven days, or bleeding so heavy you soak through a pad or tampon every hour. A month of continuous bleeding goes well beyond that threshold. Some people experience steady, lighter bleeding the entire time, while others cycle between heavy flow and spotting that never fully stops. Both patterns count as abnormal uterine bleeding and share many of the same causes.
Hormonal Imbalances
The most common reason for a month-long period is a hormonal imbalance, specifically between estrogen and progesterone. Normally, your body builds up the uterine lining with estrogen in the first half of your cycle, then produces progesterone after ovulation to stabilize that lining and eventually trigger a clean, contained shed. When you don’t ovulate, progesterone never arrives in meaningful amounts. Estrogen keeps building the lining unevenly, and it sheds in a prolonged, unpredictable way rather than in a defined period.
Polycystic ovary syndrome (PCOS) is one of the most frequent culprits. People with PCOS often go through repeated cycles without ovulating, which creates a persistently elevated estrogen-to-progesterone ratio. The uterine lining grows thick and unstable, then breaks down irregularly over weeks instead of days.
Thyroid problems, particularly an underactive thyroid, also disrupt the hormonal signaling that controls your cycle. When thyroid hormone levels are off, the chain of signals from your brain to your ovaries misfires, leading to missed ovulation and drawn-out bleeding. A simple blood test can identify thyroid dysfunction, and treatment often resolves the bleeding pattern entirely.
Structural Problems in the Uterus
Growths inside the uterus can physically interfere with how it sheds its lining. Uterine polyps are soft tissue growths that develop on the inner wall of the uterus. They’re estrogen-sensitive, meaning they grow in response to estrogen, and they cause irregular bleeding, unpredictable periods, and flows that vary widely in length and heaviness. Polyps are most common around menopause but can develop at any age.
Fibroids, which are noncancerous muscular growths in the uterine wall, cause similar problems. Depending on their size and location, they can prevent the uterus from contracting properly to stop bleeding, leading to prolonged or very heavy periods. Both polyps and fibroids show up clearly on ultrasound imaging.
Birth Control Side Effects
If you recently started a new form of hormonal birth control, that could explain weeks of bleeding. Breakthrough bleeding is common with hormonal IUDs, implants, and low-dose birth control pills, especially in the first few months. With IUDs, irregular bleeding and spotting typically improve within two to six months of placement.
Certain factors make breakthrough bleeding more likely: smoking, missing pills or taking them at inconsistent times, and using continuous-dose hormones to skip periods altogether. If you’ve been bleeding for a month after starting a new method, it doesn’t necessarily mean the method has failed, but it’s worth a conversation with whoever prescribed it, especially if the bleeding is heavy rather than light spotting.
Perimenopause
For people in their 40s (and sometimes late 30s), a month-long period can be one of the earliest signs of perimenopause. During this transition, estrogen and progesterone rise and fall unpredictably. You may skip ovulation some months, which leads to the same lining-buildup problem described above. Periods can get longer or shorter, heavier or lighter, or disappear for months before returning with a vengeance. A single prolonged bleed surrounded by otherwise normal cycles is a classic perimenopause pattern.
Less Common but Serious Causes
Bleeding disorders that affect how your blood clots can make periods last far longer than they should. These conditions are often present from a young age, but some people don’t get diagnosed until adulthood because they assumed their heavy periods were normal. Infections like chlamydia or gonorrhea can also trigger irregular bleeding, sometimes between periods or during what seems like an endlessly long one. In rare cases, prolonged bleeding is a sign of precancerous or cancerous changes in the uterine lining, which is why persistent abnormal bleeding always warrants investigation.
The Risk of Iron Deficiency Anemia
Bleeding for a month, even lightly, depletes your iron stores. Iron deficiency anemia is the most immediate health consequence of prolonged periods, and it develops faster than many people realize. Early on you might just feel more tired than usual. As it worsens, symptoms become harder to ignore: dizziness, headaches, shortness of breath during activities that used to feel easy, pale or yellowish skin, brittle nails, and a rapid or irregular heartbeat. Some people develop unusual cravings for ice, very cold drinks, or even non-food items like paper or dirt, a condition called pica that’s a hallmark of severe iron deficiency.
If you’ve been bleeding for weeks and notice any of these symptoms, your body is telling you it’s running low on the iron it needs to carry oxygen through your bloodstream.
How the Cause Gets Diagnosed
Figuring out why your period won’t stop typically involves a combination of approaches. Expect to describe your bleeding pattern in detail: how many days, how heavy, whether there are clots, and how many pads or tampons you’re going through. Keeping a simple log before your appointment helps.
Blood tests check for iron deficiency anemia, thyroid dysfunction, and clotting disorders. A pelvic ultrasound uses sound waves to look at your uterus and ovaries for fibroids, polyps, or cysts. If the ultrasound suggests something on the uterine lining, a sonohysterography (where fluid is injected into the uterus to get a clearer picture) or a hysteroscopy (where a thin camera is inserted to view the uterine interior directly) may follow. An endometrial biopsy, where a small tissue sample is taken from the lining, checks for precancerous changes and is typically recommended for people over 35 with abnormal bleeding or younger people with significant risk factors.
How It Gets Treated
Treatment depends entirely on the cause. Hormonal imbalances from PCOS or anovulation are often managed with hormonal medications that supply the missing progesterone, either cyclically or through a hormonal IUD that thins the uterine lining and dramatically reduces bleeding over time. Thyroid-related bleeding resolves when thyroid levels are corrected.
Polyps and fibroids can often be removed in outpatient procedures. For heavy bleeding that needs to be controlled quickly, there are medications that work by preventing blood clots from breaking down, which reduces blood loss during a period. If you’re soaking through two or more pads or tampons per hour for two to three consecutive hours, that’s a signal to seek emergency care rather than waiting for an office appointment.
The reassuring reality is that most causes of month-long periods are treatable once identified. The key is not to wait it out, because a month of bleeding that goes uninvestigated can recur, worsen, and quietly drain your iron levels in the meantime.