7 possible reasons you missed a period

If you’re not trying to conceive, a late period can be nerve-wracking. But it’s not until you’ve ruled out pregnancy that it becomes really stressful: Does a late or totally absent period mean something’s really wrong? Not necessarily, explained Dr. Mary Rosser, PhD, an assistant professor of obstetrics and gynecology at Montefiore Medical Center in New York.

There are actually a number of reasons for a missed period other than pregnancy. Here, 7 of the most common culprits she sees in her practice.

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The culprit: You’ve gained or lost weight

Rosser said a weight change is one of the more common reasons menstrual cycles become irregular. If you’ve recently lost or gained 10 percent or more of your body weight, you could find yourself skipping a period.

“Major weight changes, particularly when it comes to losing weight, can cause hormones to become imbalanced,” she said. “When your body is underweight or overweight, your estrogen levels change (estrogen increases when you gain weight and drops when you lose it), and you might not release an egg and have a regular period as a result.”

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The culprit: You’re working out… a lot

Just like a big weight change, extreme exercise can also knock your reproductive hormones out of sync.

“You see this a lot with marathon runners or ballet dancers, for example,” Rosser said. “Stress on the body can alter your menstrual cycle, particularly when it goes hand-in-hand with weight loss.”

The culprit: You’re stressed

It’s not just physical stress that can mess with your cycle—mental stress can have an impact, too. So if you’re going through a particularly busy time at work or handling a difficult personal situation, don’t be surprised if your period goes AWOL that month. The good news: “Any kind of stressor can cause your period to become off, but when the stressful issue is resolved, your cycle should return to normal,”  Rosser said.

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The culprit: Your medication

Certain medicines are sometimes to blame for menstrual irregularity.

“Women who are on antidepressants or other psychiatric medications may experience missed periods,” Rosser said, adding that chemotherapy drugs can have a similar effect on your cycle.

Your birth control can also be to blame.

“The IUD can make the lining in the uterus thin, and sometimes patients will miss a period as a result,” Rosser explained.

Stopping birth control pills can mess with your cycle, too; it can take a few months for your period to get back on track.

The culprit: Thyroid issues

An overactive or underactive thyroid (a gland on your neck that helps regulate your metabolism and body temperature) can impact your cycle.

“When thyroid hormone levels are unusually high or low, this could lead to menstrual changes,” Rosser said.

This is something that your doctor will need to investigate once you’ve ruled out pregnancy. She can order blood tests to check your levels, and if there’s a problem, she can prescribe appropriate medications to help regulate your hormones.

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The culprit: Perimenopause

Perimenopause is the period during which your body is making a natural shift toward menopause, when your period stops for good. For most women, perimenopause starts with menstrual irregularity sometime in your 40s, but it can also start earlier for some. You may have hot flashes and mood swings, Rosser said. Medications, like hormone replacement therapy, can help if these are bothersome.

The culprit: Your body is still changing

It’s also normal for teenagers to skip a period.

“I tell my teenage patients to think of their changing bodies like thermometers,” Rosser said. “When you increase the temperature of a thermometer, it takes awhile for the heat to catch up with the dial. Similarly, it takes awhile for your body to catch up when your hormones are changing rapidly, so you may see irregular cycles during this time.”

The bottom line? Stay calm, Rosser said. “I often have patients who come in panicked that they missed a period, but I tell them that it’s normal to have one or two imperfect cycles a year.”

This article originally appeared on Health.com.