Medically reviewed on April 24, 2023 by Jillian Foglesong Stabile, MD, FAAFP. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.
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To prepare for pregnancy, the bodies of cisgender women and people who menstruate undergo a menstruation cycle, which lasts roughly 24 to 38 days. The cycle begins when the uterus sheds its lining in the absence of a fertilized egg. 
During this stage, the tissue and blood vessels of the uterine lining are expelled from the body, and many menstruators will experience cramping, bloating, headaches, mood changes, and breast tenderness. Some may also experience fatigue, which can result from hormonal changes in addition to other factors. 
If you’re experiencing period fatigue or asking yourself, “Why am I so tired on my period?” this article explores the possible causes of tiredness throughout your menstrual cycle.
The menstrual phase, also called menses or menstrual period, is characterized by the shedding of the uterine lining. This occurs as a result of an influx of hormones, which are produced by the hypothalamus, pituitary, and ovaries.  Serotonin and estrogen levels may also decline, which can cause drowsiness as well. 
Serotonin (5-HT) is actually a neurotransmitter, but it also functions as a hormone.  It regulates many of the body’s functions related to :
Consequently, low levels of serotonin may lead to symptoms related to depression, such as low energy levels in females. 
Estrogen and serotonin are also interconnected: Estrogen regulates serotonin synthesis in the brain. This means that low estrogen levels can create a domino effect in which both serotonin and energy levels decline. 
In addition to hormonal changes, other factors can contribute to feelings of exhaustion or drowsiness during this time. These include:
Fortunately, your energy levels should start to increase again in the days following your menstrual bleeding as your hormone levels begin to balance themselves.
See related: Do Women Need More Sleep?
The follicular phase begins on the first day of your period, and it continues for 14 to 21 days, until ovulation. Accordingly, there is some overlap with menses. 
During this time, the body will begin producing two hormones: estrogen and follicle-stimulating hormone (FSH). The latter signals to the ovaries that it’s time to produce follicles, where an egg can mature. Increased estrogen will then thicken the uterine lining to prepare it for implantation. 
As estrogen levels increase, so too will the body’s energy levels. Menstruators may feel more alert, focused, and optimistic during this phase. That said, hormone imbalances can cause the body to produce too much estrogen, which is called estrogen dominance. Those with this imbalance may experience extreme fatigue, insomnia, or irregular periods. 
Around the fourteenth day of the menstrual cycle, the dominant ovary follicle will release an egg. The egg then travels down the fallopian tube and awaits fertilization.
People who menstruate are the most fertile during this time and estrogen levels are at their peak.  This means that during ovulation, menstruators may experience increased energy. However, fluctuations in hormone levels may lead to mild feelings of irritability or unease. 
During the luteal phase, the body prepares the uterus for a possible pregnancy by continuing to thicken the uterine lining. If sperm fertilized the egg, the egg is implanted into the lining. If the egg is not fertilized, your body will begin to shed the lining, and your menstrual bleeding will occur. 
Because progesterone levels increase during this phase, menstruators may begin to experience emotional and physical PMS symptoms, which can include :
During the luteal and menstrual phases of your menstrual cycle, fluctuations in hormone levels, iron deficiencies, and low blood sugar levels can contribute to feelings of tiredness or fatigue. Fortunately, energy levels often increase during the follicular stage and ovulation as estrogen levels begin to balance out.
However, if you feel you’re experiencing significant energy shifts or hormonal imbalances, consider gaining a deeper insight into your body’s unique cycle with the Everlywell At-Home Women’s Health Test. With Everlywell, you’ll receive a comprehensive hormone panel (reviewed by CLIA-certified labs and board-certified physicians) that can help you understand your symptoms so that you can confidently take the next step toward greater equilibrium. Period.