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Why your period could be late

Wondering what's going on? Here are 9 reasons why your menstrual cycle might be off.

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If your period is late, it’s important to know that this is very common and not necessarily a cause for concern. Menstrual cycles fluctuate, whether that’s due to stress, lifestyle changes, hormone imbalances, an underlying health condition, or even using birth control. The first thing to do is to rule out pregnancy and menopause. If neither of those apply to you, then there are a number of other factors that might be causing your late period. Here are the most common reasons why your period might be late.


Oh stress—the reason for so many health disturbances. Chronic stress can wreak havoc on your body, including impacting your hormones. Stress can also lead to sudden weight gain or loss and can even influence other lifestyle factors like diet, alcohol consumption, and exercise, all of which can lead to changes with your hormones and your menstrual cycle. If stress is impacting your cycle, you could notice late or missed periods. 

Weight change

Changes in body weight—both gaining or losing weight—can be triggers for an irregular or or late period. Hormones, in particular estrogen, can be impacted by these changes; since hormones control our menstrual cycle, it is very common for weight changes to impact menstrual cycles. This could include irregularities in one’s cycle or even that their period stops altogether. Part of the reason for this is that the body may interpret weight loss or gain as stress, triggering a fight-or-flight response. When this happens, the body wants to reserve and conserve the energy for essential tasks like breathing and digesting, leaving little to no energy leftover for ovulation and menstruation. 

Too much exercise

If you’re exercising a lot, and not taking in enough calories, you can experience exercise-induced amenorrhea, which happens when you don’t have a period for at least three months. This typically happens to highly active athletes who sometimes have low body fat levels and nutritional deficiencies. This can put a lot of stress on the body and can make the hypothalamus stimulate the ovaries less, pausing or stopping ovulation and menstruation.

Hormone imbalances

Hormone imbalances can affect the body in a lot of different ways, especially periods. Some underlying causes for hormone balances are diabetes, thyroid problems, stress, eating disorders, tumors, PCOS, and medications.

Certain hormones, like prolactin or thyroid hormones, can lead to a missed period or multiple missed periods. Sometimes hormonal imbalances are genetic, and sometimes they’re caused by lifestyle factors or something more serious. 

Your doctor can run specific blood tests to help you figure out what is causing your hormone imbalance.  

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Polycystic ovary syndrome (PCOS)

PCOS is a common cause of irregular periods and affects 4-20% of people assigned female at birth (AFAB) of childbearing age. It can occur when someone AFAB produces an abundance of male hormones called androgens. Excess androgens can lead to menstrual irregularities as well as excess facial hair, body hair, and acne on the face, neck, and back.

High androgen levels can also impact egg development and ovulation. Instead of the eggs maturing, ovarian cysts, which are little fluid-filled sacs, can develop on the ovaries. This can cause ovulation to stop, resulting in a late period or even a missed period for several months.

Birth Control

Birth control is one of the most common causes for menstrual changes and can sometimes lead to periods stopping altogether. Hormonal birth control contains synthetic hormones, like estrogen and progestin, that stop the ovaries from releasing eggs in order to prevent ovulation. (If you don’t ovulate, you can’t get pregnant.) These hormones can impact the timing of your period or prevent you from having a period altogether.

If you recently started or stopped taking birth control pills, using the patch or shots, or removed an IUD, your period might be late or missing for a couple months. It can take up to three months for your cycle to normalize and your period to be regular again after stopping birth control.

Thyroid issues 

An overactive or underactive thyroid gland can sometimes be the cause of a late or missed period. The thyroid gland produces thyroid hormones which controls how fast you burn calories and how fast your heart beats.

Thyroid issues can cause your period to be light, heavy, irregular, and can even make your period stop for a few months, a condition called amenorrhea. 

If you think you might have a thyroid issue, talk to your health care provider. 



Almost all medications come with some sort of side effect, and they can impact different people’s bodies in different ways. Here are a few known medications that could make your period late or completely stop:

Thyroid medication

Hypothyroidism is when your thyroid doesn’t produce enough thyroid hormone, which can lead to irregular periods. Medications to treat this, like levothyroxine, can cause irregular, late, or missed periods. 


Some antidepressants, such as Prozac or Wellbutrin, can impact your cycle and lead to irregular or delayed periods, especially within the first three months as your body adjusts to the medication.

Epilepsy medication

Some people who take epilepsy medication have experienced late, missed, or irregular periods. If you are, talk to your health care provider to rule out any other underlying conditions.


Chemotherapy is a cancer treatment that can greatly impact people’s menstrual cycles. This can look like an irregular cycle, heavier flow, or even your period stopping altogether.


If your period is more than a week late, pregnancy could be the reason. If the above potential reasons don’t apply to you, it’s best to take a pregnancy test and know for sure. If you are pregnant, and you don’t want to be, you have options

Hey Jane offers safe, discreet, and convenient medication abortion care online. We have sliding scale pricing, work with a number of insurance providers, and partner with abortion funds to ensure that cost is never a barrier to getting the care you need. Consult with a Hey Jane provider now to see if you're eligible. 

Not pregnant but curious about better birth control options? Find a birth control option that’s best for you and your lifestyle.

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