Young woman lying on couch and wondering "Why am I so tired on my period?"

Why am I so tired on my period?

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.

Table of contents

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. [1]

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. [2]

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.

Energy levels during the menstrual phase

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. [3] Serotonin and estrogen levels may also decline, which can cause drowsiness as well. [3]

Serotonin (5-HT) is actually a neurotransmitter, but it also functions as a hormone. [4] It regulates many of the body’s functions related to [4]:

  • Body temperature
  • Sexual arousal
  • Appetite
  • Sleep

Consequently, low levels of serotonin may lead to symptoms related to depression, such as low energy levels in females. [4]

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. [5]

In addition to hormonal changes, other factors can contribute to feelings of exhaustion or drowsiness during this time. These include:

  • Iron deficiency – Periods, specifically heavy periods, can lead to large amounts of blood loss. As a result, people who menstruate can experience a condition called iron deficiency anemia if there’s not enough iron in the body. Symptoms often include fatigue, dizziness, and lightheadedness. [6]
  • Disrupted sleep – Serotonin plays a role in the production of melatonin, a hormone produced by the brain that helps to regulate the body’s circadian rhythms and supports healthy sleep cycles. Low serotonin levels during menses can disrupt the production of melatonin, which can cause insomnia and, subsequently, tiredness the next day. [4]
  • Elevated glucose levels – In the days or weeks leading up to a period, the body can experience hormonal changes that can decrease blood sugar levels and increase cravings for sugary or high-carb foods. [7] While these types of treats can briefly elevate serotonin levels, overconsumption can also inversely affect blood sugar levels. As a result, people may experience tiredness, weakness, confusion, and dizziness. [8]

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?

Energy levels during the follicular phase

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. [9]

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. [9]

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. [14]

Womens Health support

Energy levels during ovulation

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. [10] This means that during ovulation, menstruators may experience increased energy. However, fluctuations in hormone levels may lead to mild feelings of irritability or unease. [11]

Energy levels during the luteal phase

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. [12]

Because progesterone levels increase during this phase, menstruators may begin to experience emotional and physical PMS symptoms, which can include [13]:

  • Period fatigue
  • Lethargy
  • Tiredness
  • Brain fog
  • Mood swings
  • Irritability
  • Anxiety
  • Depression
  • Insomnia
  • Food cravings

Track your health and wellness with Everlywell

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.

Understanding low energy levels in females

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What This Women’s Hormone Test Can Reveal About Your Health


  1. Menstrual cycle. Cleveland Clinic. Published December 9, 2022. Accessed April 9, 2023.
  2. Epperson C, Amin Z. Interactive effects of estrogen and serotonin on brain activation during working memory and affective processing in menopausal women. Psychoneuroendocrinology. Published August 5, 2011. Accessed April 9, 2023.
  3. Reed B, Carr B. The normal menstrual cycle and the control of ovulation. Endotext. Published August 5, 2018. Accessed April 9, 2023.
  4. Serotonin. Cleveland Clinic. Published March 18, 2022. Accessed April 9, 2023.
  5. Bashaw M, Pathak D, Moody S, Gilder R. An overlooked connection: serotonergic mediation of estrogen-related physiology and pathology. BMC Womens Health. doi: 10.1186/1472-6874-5-12. Accessed April 9, 2023.
  6. Iron-deficiency anemia. National Heart, Lung, and Blood Institute. Published March 24, 2023. Accessed April 9, 2023.
  7. Krishnan S, Tryon R, Welch L, Horn W, Keim N. Menstrual cycle hormones, food intake, and cravings. The FASEB Journal. Published April 1, 2016. Accessed April 9, 2023.
  8. Low Blood Sugar (Hypoglycemia). CDC. Published December 30, 2022. Accessed April 9, 2023.
  9. Follicular phase. Cleveland Clinic. Published August 8, 2022. Accessed April 9, 2023.
  10. Ovulation. Cleveland Clinic. Published July 8, 2023. Accessed April 9, 2023.
  11. Rebollar A. Comparison of affect changes during the ovulatory phase in women with and without hormonal contraceptives. doi: 10.1016/j.heliyon.2017.e00282. Accessed April 9, 2023.
  12. Luteal phase. Cleveland Clinic. Published November 4, 2022. Accessed April 9, 2023.
  13. Premenstrual Syndrome. Cleveland Clinic. Published October 12, 2022. Accessed April 9, 2023.
  14. High estrogen. Cleveland Clinic. Published February 9, 2022. Accessed April 9, 2023.
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