Reasons for a Late Period That Aren't Pregnancy

If you're waiting on a delayed period, you may wonder whether you're pregnant. But pregnancy isn't the only reason your period could be late. Common reasons you may miss a period when you aren't pregnant include hormonal birth control, hormone-related health conditions, stress, and perimenopause.

"Everybody thinks they're pregnant when their period is late," says Wendy Goodall McDonald, MD, aka Dr. Every Woman of Women's Health Consulting in Chicago. And if you've engaged in any sexual activities that included semen being introduced in or around the vagina, that's not a bad guess. But before you run to the pharmacy to pick up an at-home pregnancy test, read about the many things that can cause a late period when you're not pregnant.

Possible Causes of a Late Period When You're Not Pregnant

An abnormal cycle is one that is different in some way from a typical period, which can mean different things for different people. A missed, delayed, or late period that isn't caused by pregnancy is considered one type of abnormal cycle.

During an abnormal cycle, your period could be longer or shorter than usual. It also might come earlier or later than anticipated. The flow could be heavier or lighter than usual or could stop and start but still last the same number of days overall. You might also experience spotting or bleeding in between your periods or you might have more or less cramping than you normally do.

Below are some things that might cause a late period that aren't pregnancy.

Your birth control

Hormonal birth control can cause abnormal periods. Intrauterine devices (IUDs) and the Depo-Provera shot, for example, can cause irregular or "late" periods. And if you're talking birth control pills, skipping the inactive pills can cause you to miss the days you would normally bleed.

Though people often think that birth control pills "regulate" your hormones and your period, the bleeding people experience during the week of inactive pills is withdrawal bleeding, not a true period. That's because hormonal birth control methods like the pill effectively override your body's natural hormone cycle.

When you keep taking the active pills for more than the usual 21 days, the lining of the uterus stays stable, says George Patounakis, MD, PhD, FACOG, an attending physician at Reproductive Medicine Associates of Florida. That means the uterine lining won't shed and you won't experience bleeding.

But once you take the inactive pill, hormone levels drop and trigger bleeding, he explains. "It's not a period the way you would think of in someone who's not taking birth control because it's induced by medication and not by normal processes."

Polycystic ovary syndrome (PCOS)

People with polycystic ovary syndrome (PCOS) may experience late periods. That's because people with PCOS often have additional follicles, making the menstrual cycle take longer.

During a typical menstrual cycle, each ovary develops roughly five follicles. Those follicles compete to become the dominant one that releases a mature egg at ovulation. When you have PCOS, your egg may release later. No released egg means no period.

Other common PCOS symptoms include weight gain and increased levels of the androgenic hormone, testosterone, which can cause thick hair growth on the face and breasts. But even without these symptoms, you can't rule out PCOS.

"There are people who are not overweight and don't have extra hair who have irregular cycles, and an ultrasound will show they have excessive follicles," says Anuja Vyas, MD, FACOG, with Houston Methodist Obstetrics and Gynecology Associates.

Stress

"Emotional distress can affect the region of the brain that controls the pituitary gland, which regulates the hormones that stimulate our ovaries," explains Dr. Vyas. As a result, stress can sometimes cause a late period.

But it's important to note that every person experiences stress differently, so its effect on the menstrual cycle is highly subjective, says Dr. McDonald. For example, moving across the country or dealing with a challenging work project could throw off one person's period, but the same situation might not affect another person's period.

Significant weight changes

Losing or gaining a lot of weight can be another reason for late periods. "Severe weight loss can shut down the hypothalamus's production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) that regulate the ovaries," says Dr. Vyas. Without FSH and LH, the menstrual cycle is interrupted.

Sudden significant weight loss is common with certain health conditions, eating disorders, and crash diets. It's also common with the use of weight loss medications like GLP-1 agonist drugs such as Ozempic (semaglutide).

Gaining weight can have a similar effect, primarily when related to conditions like PCOS. People with PCOS may be extra sensitive to weight gain and loss. People with obesity may also experience changes in their hormone levels that impact their periods.

Intense exercise

Very intense or strenuous exercise can also impact your menstrual cycle. Though most common in professional athletes and people who regularly train hard (think: marathon runners, triathletes, etc.), excessive training or starting a new intense exercise routine can put your body into a constant state of calorie deficit and increase the production of hormones that impact your menstrual cycle.

Your age

Irregular or abnormal periods are especially common around the time a person first starts menstruating and as they near the end of menstruation (known as menopause). Menstrual cycles take time to regulate. In the first several years of menstruation, it's common for cycle lengths to vary, sometimes significantly, which can make it difficult for young people to know when to expect their next period.

On the opposite end of the spectrum, older adults people who menstruate can experience abnormal cycles including late periods due to conditions like primary ovarian insufficiency (POI) or premature or early menopause. The transition to menopause known as perimenopause also affects a person's period.

Perimenopause

The average American who menstruates experiences menopause at age 51, but before that, they go through a transitional period known as perimenopause. During this time, which usually starts in your 40s, some people have abnormal menstrual cycles.

Instead of the average 28 days between periods, menses may arrive 36 to 48 days apart. "If you're under 45 and your period stops completely, it's possible you're going through early menopause or experiencing premature ovarian failure," Dr. Vyas adds.

Pituitary tumor

Though it's rare and unlikely, sometimes a prolactinoma—a pituitary tumor that secretes excess amounts of prolactin, the hormone that signals breast milk production—is to blame for a late period.

Dr. Vyas says people experiencing irregular periods, headaches, blurry vision, and discharge from the breasts even though they're not breastfeeding may want to get checked by a health care provider for this type of tumor.

Diabetes and thyroid disease

Jay M. Berman, MD, FACOG, chief of gynecological services at Detroit Medical Center's Harper Hutzel Hospital and professor of obstetrics and gynecology at Wayne State University, says other issues such as diabetes and thyroid disease may be to blame for a late period.

According to the US Department of Health and Human Services's Office on Women's Health, thyroid disease can cause problems with your period because thyroid hormones help control your menstrual cycle. Unbalanced thyroid hormones can cause your period to be irregular.

In addition, some studies have found a link between type 1 diabetes and early menopause. Researchers believe this occurs because this type of diabetes causes premature vascular aging and, in turn, ovarian aging. As you reach early menopause, your periods may be late and irregular.

Medication

Certain medications can impact your menstrual cycle and potentially cause late periods, such as:

• Antipsychotics
• Antidepressants
• Chemotherapy
• Hormonal birth control
• Hormone therapy
• Steroids

If you've started a new medication or supplement and are experiencing late periods or abnormal cycles, talk to a health care provider.

When To Visit a Health Care Provider

Many factors can affect the length and regularity of your periods, so the reason behind an occasional late period may not be apparent, according to Dr. Berman. But if it's frequently happening or you're experiencing other symptoms, speak to a health care provider.

"Many people will, for various reasons, occasionally not ovulate, and this can cause an early or delayed menses," he says. "Depending on [the person's] history, it may require further testing to determine the cause."

Make an appointment with a health care professional if you can't pinpoint the reasons for a late period, as your provider may want to check for specific health conditions. It's also important to note that vaginal bleeding after a late period may not actually be your period.

"Anybody who experiences heavy bleeding and pain after a missed period and/or a positive pregnancy test should go to the doctor," says Dr. McDonald, as not all bleeding is a period, especially in a setting where something is off.