The Role of Hormones in the Menstrual Cycle

• Researched and written by: Dr. Akshara C H, MBBS

• Medical inputs by: Dr Yash Bahuguna, MBBS, MS, DNB, ISGE Certified Practitioner for PCOS

• Medically reviewed by: Dr Poonguzhali Liston, MBBS, MS OBG, FMAS, DRM, FRM, CIMP

 

TL;DR

• Hormones drive every stage of the menstrual cycle, from bleeding to ovulation and hormone‑related symptoms.[1]

• Signals from the brain stimulate the ovaries to release estrogen and progesterone in a carefully timed sequence.[1,3]

• These hormone shifts prepare the uterus for pregnancy and influence mood, energy, digestion, sleep, and appetite.[1,4,5]

• Differences in hormone timing and sensitivity help explain why menstrual cycle experiences vary widely between women.[2]

 

Hormones Responsible For the Menstrual Cycle

Your menstrual cycle is controlled by hormones that carry signals between your brain, ovaries and your uterus. These signals change continuously across the month, and your body responds to them in coordinated ways. As hormone levels rise and fall, they determine when ovulation occurs, when your period begins, and why you may notice physical or emotional changes at different points in your cycle.[1,3]

Several key hormones are involved, including gonadotropin releasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. Rather than acting in isolation, these hormones work together to guide the cycle smoothly from one phase to the next.[1,3]

Brain Hormones (FSH and LH): How the Cycle Starts

Your menstrual cycle begins in the brain, in an area called the hypothalamus, which helps coordinate hormone signalling throughout the body. The hypothalamus secretes gonadotropin‑releasing hormone (GnRH). GnRH acts as the starting signal for the menstrual cycle and helps set the rhythm for other reproductive hormones.[1,3]

GnRH stimulates the pituitary gland, a small hormone‑releasing structure at the base of the brain. In response, the pituitary releases follicle‑stimulating hormone (FSH) and luteinizing hormone (LH) into the bloodstream. These hormones travel to the ovaries and guide key steps of the cycle, including egg development and ovulation.[1,3]

Follicle‑stimulating hormone (FSH)

FSH supports the early stages of egg development each cycle. It helps select and stimulate the growth of small fluid‑filled sacs in the ovaries called follicles, each of which contains an immature egg.

At the start of a cycle, several follicles may begin to develop at the same time. Usually, one follicle becomes dominant and continues to mature. As this follicle grows under the influence of FSH, it produces increasing amounts of estrogen. Rising estrogen levels signal that the cycle is progressing as expected.[1,2,3]

Luteinizing hormone (LH)

LH plays a central role in ovulation, the release of an egg from the ovary. As the dominant follicle matures, estrogen levels continue to rise.

When estrogen remains high for long enough, it sends a signal back to the brain to release a larger amount of LH. This increase, known as the LH surge, triggers ovulation. In a typical 28‑day cycle, ovulation often occurs around the middle of the cycle, although this timing can vary from month to month. Such variation is common and medically normal.[1,3]

Role of Hormones Released by the Ovary

Once the ovaries receive signals from the brain, they begin estrogen and progesterone production. These hormones shape the remainder of the cycle by supporting ovulation, preparing the uterus for a possible pregnancy, and triggering menstruation if pregnancy does not occur.[1,2,3]

Estrogen

Estrogen is most active during the first half of the menstrual cycle, before ovulation. It is mainly produced by the growing ovarian follicle and gradually rises as ovulation approaches.

One of estrogen’s primary roles is to thicken the lining of the uterus, creating a supportive environment for a potential pregnancy.[1,3]

Estrogen also interacts with brain systems involved in mood, focus, and emotional regulation. Shifts in estrogen levels may contribute to changes in concentration, irritability, or low mood, particularly in the days leading up to a period.[1,2,6]

Progesterone

After ovulation, a temporary structure called corpus luteum gets formed in the ovary after the egg is released. The corpus luteum secretes progesterone, making it the dominant hormone. 

Progesterone helps stabilise and maintain the uterine lining (endometrium) during the second half of the cycle, keeping the body prepared in case pregnancy occurs. During this phase, some women notice a small rise in resting body temperature.[1,3]

As progesterone levels later fall, particularly in the days before a period, some women experience lower energy, fatigue, or emotional changes. These experiences vary widely and are influenced by individual hormone sensitivity.[6]

Hormone Changes and Your Period

If pregnancy does not occur, estrogen and progesterone levels fall toward the end of the cycle. This drop signals the body to shed the uterine lining, resulting in menstruation.

Around this time, some women notice mood changes, increased sensitivity to pain, or physical discomfort. These symptoms are linked to hormone withdrawal and local chemical signals in the uterus rather than to a single hormone acting alone.[1,3,6]

Hormonal Flow Across the Menstrual Cycle

Hormones follow shifting patterns across the menstrual cycle. At different points, certain hormone levels rise while others fall, and your body responds to these combined changes rather than to one hormone in isolation.

Menstrual phase

At the beginning of the cycle, estrogen and progesterone levels are low. This hormonal drop causes the uterine lining to shed, which is your period. During this time, uterine contractions help clear the lining.[1,3]

Early follicular phase

Soon after bleeding begins, FSH levels rise. This stimulates the ovaries to develop follicles, each containing an egg. As follicles grow, estrogen production increases, marking the transition into the next phase of the cycle.[1,3]

Late follicular phase

As estrogen levels rise, the uterine lining rebuilds in preparation for a possible pregnancy. Estrogen also affects the brain, influencing systems involved in mood and emotional regulation. Some women notice changes in focus, confidence, or emotional balance during this part of the cycle.[1,2]

Time of ovulation

Sustained high estrogen levels trigger ovulation. An egg is released from the ovary, typically around the middle of the cycle in a 28‑day pattern, although exact timing varies between individuals and cycles.[1,3]

Luteal phase

Following ovulation, progesterone levels rise. Progesterone supports the uterine lining and helps regulate the second half of the cycle. A small increase in resting body temperature may occur during this time.[3]

Premenstrual phase (Late luteal)

If pregnancy does not occur, estrogen and progesterone levels gradually fall. As hormone support declines, some women experience increased emotional sensitivity or physical symptoms.[2]

As hormone levels fall further, the uterine lining is shed and the next period begins, marking the start of a new cycle.[1,3]

Other Hormone‑Related Signals Involved in the Menstrual Cycle

In addition to the main cycle hormones, several other hormone‑related signals play supporting or local roles.

Anti‑Müllerian hormone (AMH)

Anti‑Müllerian hormone (AMH) is produced by small developing follicles in the ovaries. It does not control ovulation or cycle timing. Instead, AMH reflects the number of follicles present and is commonly used as a marker of ovarian reserve, which estimates the remaining egg supply.[1,2]

Prostaglandins 

Prostaglandins are locally produced chemical messengers in the uterine lining. They drive uterine contractions and support shedding of the lining during menstruation. Through these effects, prostaglandins influence cramps, bowel changes, and pain, affecting how a period feels rather than when ovulation occurs.[1,2]

GnRH, FSH, LH, estrogen, and progesterone control the timing and structure of the menstrual cycle. AMH provides background regulation of follicle activity, while prostaglandins mainly influence period symptoms rather than cycle timing.[1,2]

Factors That Can Influence Hormonal Patterns

Hormonal patterns across the menstrual cycle can be influenced by everyday health factors and life demands. These influences may affect cycle regularity, ovulation timing, or how the cycle feels from month to month.[1,2]

Stress and emotional load

Ongoing physical or emotional stress can reduce or delay hormone signals from the brain, including those that regulate FSH and LH release. When stress is persistent, ovulation may be delayed or cycle timing may shift.[1,2]

Sleep disruption

Poor sleep, shift work, or irregular sleep schedules can interfere with communication between the brain and the hormone system that controls the menstrual cycle. Over time, this may affect how consistently ovulation occurs.[1,2]

Exercise and training load

Exercise alone does not disrupt the menstrual cycle. Hormone changes across the cycle can influence how the body responds to training, including strength and recovery. Cycle disruption is more likely when training intensity is very high and not supported by adequate nutrition or rest, reflecting the body prioritising basic energy needs.[2,3]

Thyroid or ovarian conditions

Conditions affecting the thyroid gland or the ovaries can alter hormone production and feedback between the brain and ovaries. This may change cycle length, ovulation timing, or bleeding patterns and usually requires medical evaluation.[1,2]

Note: Oral contraceptive pills (OCPs)

Oral contraceptive pills affect the menstrual cycle differently depending on the formulation.

Combined oral contraceptive pills, which contain estrogen and progestin, suppress ovulation by reducing FSH and LH secretion. Bleeding during pill‑free intervals is withdrawal bleeding rather than a natural menstrual period.[4,5]

Progestin‑only pills may suppress ovulation in some cycles but not consistently in all users. Their primary effects include thickening cervical mucus and altering the uterine lining, and bleeding patterns may be irregular.[4,5]

When to See a Doctor

Although hormonal changes across the menstrual cycle are common, certain patterns are worth discussing with a healthcare provider. These include:

• Irregular or missed periods
  

• Difficulty ovulating when trying to conceive
  

• Symptoms that interfere with daily life
  

• Sudden changes in bleeding
  

• Symptoms occurring outside expected cycle timing

Seeking medical advice does not automatically mean something is wrong. Many cycle‑related concerns are common and manageable, especially when discussed early. Timely consultation may help clarify what is happening, rule out underlying conditions, and guide appropriate follow‑up.

The Bottom Line

Hormones are the central drivers of the menstrual cycle. Signals from the brain guide the ovaries to release estrogen and progesterone in a coordinated sequence that supports ovulation, potential fertilisation, and preparation of the uterus for pregnancy. When pregnancy does not occur, falling hormone levels reset the system and the cycle begins again.

Because hormone levels rise and fall at different speeds in different people, menstrual cycles do not all feel the same. Differences in hormone timing, sensitivity, and life stage help explain why symptoms vary and experiences change over time, even when cycles are considered medically normal.

FAQs on Hormones Regulating the Menstrual Cycle

Which hormone starts the menstrual cycle?

Rising follicle‑stimulating hormone released from the pituitary gland initiates development of ovarian follicles.

What hormone triggers ovulation?

A surge in luteinizing hormone triggers ovulation once estrogen remains elevated for long enough.

Can hormone levels be normal but symptoms still occur?

Yes. Many symptoms relate to sensitivity to hormone changes rather than abnormal hormone levels.

Do hormones affect fertility even with regular periods?

Yes. Fertility depends on coordinated hormone timing that supports ovulation and implantation, not bleeding alone.

Can stress affect the menstrual cycle?

Yes. Stress can delay or alter ovulation by disrupting hormone signalling, even when hormone levels appear normal.

References

1. Reed BG, Carr BR. The normal menstrual cycle and the control of ovulation.

2. Thiyagarajan DK, Basit H, Jeanmonod R. Physiology, menstrual cycle. InStatPearls [Internet] 2024 Sep 27. StatPearls Publishing.
   

3. Kissow J, Jacobsen KJ, Gunnarsson TP, Jessen S, Hostrup M. Effects of follicular and luteal phase-based menstrual cycle resistance training on muscle strength and mass. Sports Medicine. 2022 Dec;52(12):2813-9.
   

4. American College of Obstetricians and Gynecologists. Combined Hormonal Birth Control: Pill, Patch, and Ring. Accessed December 15, 2025.
   

5. NHS Inform. Combined pill. Accessed December 15, 2025.

6. Yonkers KA, O'Brien PS, Eriksson E. Premenstrual syndrome. The Lancet. 2008 Apr 5;371(9619):1200-10.