Does Tamoxifen Stop Periods?

Medically reviewed by Dr. Doug Blayney on March 8, 2024

When we talk about breast cancer, it's important to know that there are different types of it. In the United States and many Western countries, the most common type is called hormone-positive or estrogen receptor-positive breast cancer. This kind of cancer relies on hormones, like estrogen and progesterone, to signal  the cancer cells to grow. Doctors can treat this type of cancer with anti-hormone therapies that block the hormones' actions, slowing down or stopping the cancer from growing. One of these medicines is Tamoxifen, which is taken as a pill every day. Tamoxifen works by blocking the estrogen signal that tells the cancer cells to grow. It can help lower the chance of the cancer coming back and spreading. However, like many medicines, Tamoxifen has side effects. One common question people ask is whether Tamoxifen stops a woman from having her period, and we'll explore that in more detail in the article below. As someone who was on Tamoxifen for many years, I can tell you that one of the side effects I enjoyed the most from a logistical standpoint, was the reduction in my periods… but there are certainly pros and cons that are associated with the interruption to menstruation.

Tamoxifen and Breast Cancer

There are several subtypes of breast cancer, but the main ones are divided into three common categories (note that there can be overlap between the first two categories):

Hormone Receptor-Positive Breast Cancer: This type of breast cancer is sensitive to hormone  – like estrogen and progesterone signaling . It includes subtypes like estrogen receptor-positive (ER+), progesterone receptor-positive (PR+), or both (ER/PR+).

HER2-Positive Breast Cancer: In this subtype, the cancer cells have too much of a protein called HER2, which acts to auto-signal or self signal the cancer to grow. 

Triple-Negative Breast Cancer: This type does not have hormone receptors (ER/PR) or excess HER2 protein.

Tamoxifen is a medicine that some people use when they are diagnosed with Hormone Receptor-Positive Breast Cancer. Imagine each cancer cell as a little car, and hormones like estrogen and progesterone act like signals, allowing these cells to spread. Doctors want to prevent these signals, so they try to stop (or block) estrogen or progesterone from being in the body or reaching the "gas pedal" of the cancer cells. The idea is that by removing the signal for growth, we can reduce the risk of cancer cells growing and spreading. That's why Tamoxifen is referred to as a hormone-blocking medicine.

The effect of Tamoxifen on Menstrual Cycles

Tamoxifen, a medication used for Hormone Receptor-Positive Breast Cancer, can impact menstrual cycles in different ways for different people. Some individuals may experience changes in their menstrual cycles while taking Tamoxifen. For some, their periods may become irregular or stop altogether. It's important to note that the effects can vary from person to person. While some may notice significant changes, others might not experience much difference in their menstrual cycles at all. Doctors carefully monitor and discuss these variations with each individual to better understand and manage the effects of Tamoxifen on their menstrual cycles. 

A Brief Note on Menstruation

Menstruation is a sign of the shedding of the uterine lining if no fertilized egg is implanted.  The menstrual cycle is regulated by the ovarian-pituitary axis, and the hormones secreted by the pituitary and the ovary. The onset of menstruation or menarche, usually occurs in the early teenage years, and menstruation stops at menopause.  The best predictor of the age at which menopause occurs is the age when one’s mother went through menopause.  

Naturally occuring menopause, that is not induced by taking out the ovaries, rarely occurs abruptly. The ovaries usually go through several months to several years of sputtering out  – the ovaries gradually lose their function of releasing eggs and gradually taper the amount of estrogen and progesterone which is secreted each menstrual cycle.  

Many conditions can interfere with the menstrual cycle, and produce a temporary menopause.  Chemotherapy drugs can damage the ovaries so that they don’t produce estrogen, progesterone, and eggs. Widespread cancer or other serious illness, starvation, elite-level athletic training and serious infections can also result in failure of the ovaries.

After completion of chemotherapy, ovarian function, and menstruation can return.  Return of ovarian function is age related. Younger women, that are less than 30 years old, almost always have a return of ovarian function. The chances of the return of ovarian function as the age of menopause approaches becomes less and less.

Why do Menstrual Changes Occur?

So why does Tamoxifen impact our period? Let’s first think about what the hormones estrogen and progesterone are meant to do for our body if we are healthy and unconcerned about cancer (wouldn’t that be nice?!).

What is estrogen?

Estrogen is a hormone that plays important roles in our bodies, especially in girls and women, though estrogen is present in men as well. Its main purpose is to help control and regulate things like the menstrual cycle and the development of female characteristics, such as breast growth, hair patterns, and a deeper voice. Estrogen also helps keep bones strong and healthy. It's like a natural messenger that tells the body what to do, and it's important for normal growth and functioning, particularly during puberty and in women's reproductive years. Here are some of the main roles of estrogen:

1. Regulating the Menstrual Cycle: Estrogen helps control the menstrual cycle in women, including the release of eggs from the ovaries.
2. Promoting Breast Development: During puberty, estrogen is responsible for the growth and development of breast tissue.
3. Maintaining Bone Health: Estrogen plays a role in keeping bones strong and healthy. It helps prevent bone loss and reduces the risk of osteoporosis.
4. Supporting Pregnancy: Estrogen levels rise during pregnancy and help maintain the uterine lining, necessary for a successful pregnancy.
5. Affecting Mood and Memory: Estrogen can influence mood and memory, and changes in estrogen levels are linked to mood swings and cognitive changes.
6. Skin Health: It contributes to skin health by maintaining skin thickness and promoting collagen production.
7. Vaginal Health: Estrogen helps maintain the health of the vaginal lining and can affect lubrication and elasticity.
8. Metabolism and Cholesterol: Estrogen has an impact on metabolism and can help control cholesterol levels in the blood.

What is progesterone?

Progesterone is another important hormone in our bodies, and its main purpose is to help prepare a woman's body for a possible pregnancy. It's like a helpful caretaker for the uterus. If a woman's egg gets fertilized by a sperm, progesterone helps make the uterus (womb) ready to support the growing baby. If there's no pregnancy, progesterone levels drop, leading to the start of the menstrual period. So, progesterone helps control the menstrual cycle and is a key player in pregnancy, making sure everything is ready for a baby if one is on the way. Here are some of the main roles of progesterone:

1. Preparing the Uterus: One of its primary roles is to prepare the lining of the uterus (womb) for a possible pregnancy. If an egg is fertilized by sperm, progesterone helps make the uterus a suitable place for the fertilized egg to implant and grow.
2. Regulating the Menstrual Cycle: Progesterone helps control the menstrual cycle by maintaining the uterine lining. If there is no pregnancy, a drop in progesterone levels triggers the start of the menstrual period.
3. Supporting Pregnancy: During pregnancy, progesterone levels remain high, maintaining the uterine lining and reducing the chances of miscarriage. It also helps relax the uterine muscles to prevent contractions.
4. Affecting Mood and Sleep: Progesterone can influence mood, making some women feel more relaxed or even drowsy. This hormone can also affect sleep patterns.
5. Breast Health: It plays a role in maintaining healthy breast tissue.
6. Cervical Mucus: Progesterone can affect cervical mucus, making it thicker and less receptive to sperm during non-fertile periods of the menstrual cycle.

So if we are blocking estrogen and/or progesterone, why might our menstrual cycle be impacted?

Blocking estrogen and progesterone, which we talked about above, can affect the menstrual cycle. Think of these hormones like messengers that tell the body it's time for the uterus lining to build up and prepare for a possible pregnancy. When someone takes medicine like Tamoxifen to block these hormones, it disrupts this natural process. Without the usual signals, the uterus lining might not build up as much, leading to changes in the menstrual cycle. Some women may experience irregular periods or even stop having periods altogether. It's all part of the medicine's way of slowing down or stopping the growth of cancer cells that rely on these hormones. This study looked at 59 pre-menopausal women, 36 who had no period after Tamoxifen use and 23 who continued to menstruate. Hormone levels were measured and levels of luteinizing hormone and estradiol were not statistically different according to the presence of menstruation. The impact on the menstrual cycle varies from person to person, and doctors keep a close eye on these changes to ensure the treatment is working as intended.

It’s often confusing when starting tamoxifen shortly after completing a course of chemotherapy.  The ovaries may be stunned or damaged by the chemotherapy, and temporary menopause is occurring.  Adding the effect of tamoxifen may delay the onset of ovarian cycling and menstruation even more.

Pregnancy:  Another cause of temporary menopause

Don’t forget that pregnancy also interferes with menstruation.  The secretion of eggs can occur before the ovaries are healthy enough to secret enough estrogen and progesterone to start menstruation.   Tamoxifen is a lousy contraceptive – do not rely on recovery from chemotherapy and start of tamoxifen for birth control. Use a barrier method for contraception during this time!

Managing Menstrual Changes and Side Effects

Some of the side effects of taking Tamoxifen might include:

• Menopause-like symptoms, including hot flashes, night sweats and vaginal dryness
• Weight gain (more common) or fluid retention (edema)
• Changes in menstrual periods for some women
• Tiredness or fatigue
• Changes in mood, like feeling sad or irritable
• Changes in how the uterus (womb) feels
• Hair thinning or hair loss
• Changes in the skin, like rashes or itching

Rarely, tamoxifen may cause serious issues such as:

• Blood clots, deep vein thrombosis (DVT) and strokes.
• Cataracts or other eye problems.
• Endometrial (uterine) cancer.

These side effects can vary from person to person, and also the duration of time since completing chemotherapy.  It's important to talk to a doctor about any concerns or discomfort when taking Tamoxifen.

What to do about menstrual side effects from Tamoxifen

I’m not going to lie, I enjoyed not having a period while on Tamoxifen. It was one of the few side effects that I found to be a “bonus” from the cancer experience. That being said, there were a number of additional side effects that came along with being pushed into a menopausal state, which weren’t quite so fun. Here are some tips to manage the menstrual side effects from Tamoxifen:

1. Regular Check-ups: Schedule regular appointments with your doctor to monitor and discuss any changes in your menstrual cycle while taking Tamoxifen.
2. Open Communication: Keep an open line of communication with your healthcare provider about any concerns or changes you notice in your menstrual cycle.
3. Hormone Replacement Therapy (HRT): In some cases, doctors may recommend hormone replacement therapy to manage the side effects. This involves providing the body with hormones it no longer produces due to Tamoxifen.  Vagnial estrogen can be helpful to reduce vaginal dryness or pain associated with urination.  Most oncologists understand that the amount of estrogen absorbed from the local application of estrogen is minimal and not a health threat.
4. Lifestyle Modifications: Maintain a healthy lifestyle through regular exercise and a balanced diet, which may help manage some of the side effects. (Had to throw this “oldie but goodie” in – but we do realize that aligning this during the best of times is challenging, let alone while dealing with cancer. So be sure to give yourself grace with this.)
5. Stay Hydrated: Drinking plenty of water can be helpful in managing symptoms associated with irregular periods.
6. Dietary Changes: Some individuals find that certain dietary changes, such as reducing caffeine intake or avoiding certain foods, may alleviate menstrual side effects. I found caffeine to really increase my hot flashes, but I adore coffee, so it was a “heated” side effect I was willing to bear to continue enjoying my morning cup of joe.
7. Alternative Therapies: Explore alternative therapies like acupuncture or yoga, which some individuals find helpful in managing menstrual symptoms.
8. Emotional Support: Seek emotional support through friends, family, or support groups, as managing these side effects may also involve emotional challenges. This was particularly helpful for me as I found the “new normal” after cancer very difficult to mentally adjust to. My therapist helped me process this, and I’m so grateful. Asking for help is not a sign of weakness.
9. Medication Adjustments: Work closely with your healthcare provider to adjust the medication dosage or explore other medications if necessary.

Remember, it's essential to consult your healthcare provider before making significant changes to your lifestyle, especially while taking Tamoxifen. They can provide personalized guidance and recommendations based on your individual needs and health. If you need a great place to keep track of your symptoms and make notes to go over with your doctor, check out our Manta Planner, which will help you stay organized. Everyone is different, and it’s important to communicate with your care team to come up with a plan that’s best for you.

Coping with Menopausal Symptoms

There are a number of menopausal symptoms that can accompany Tamoxifen treatment for premenopausal women including:

• Hot Flashes: Many women may experience sudden and intense feelings of heat, often accompanied by sweating, which can be a common symptom of menopause.
• Dress in layers to easily adjust to temperature changes, keep a fan nearby, and try deep-breathing exercises to manage hot flashes. Some foods (like caffeine) might increase the incidence and severity of hot flashes, so you can reduce your intake (or ignore it like me, and stick with your routine morning cup of coffee for emotional reasons!).

• Irregular Periods: Menstrual cycles may become irregular or stop altogether, leading to changes in the usual pattern of menstruation.
• Maintain a menstrual calendar to track changes, and discuss irregularities with your healthcare provider for personalized guidance.
• Vaginal Dryness: A decrease in estrogen levels can result in vaginal dryness, discomfort, or pain during intercourse.
• Use water-based lubricants during intercourse, stay hydrated, and consult with your healthcare provider about moisturizing products or topical estrogen.
• Mood Swings: Hormonal fluctuations can contribute to mood swings, irritability, and changes in emotional well-being.
• Practice stress-reducing techniques like meditation or yoga, and consider talking to a therapist for additional emotional support. (Therapy was the best thing that came out of my cancer diagnosis - just my 2 cents!)
• Fatigue: Feeling unusually tired or fatigued can be a symptom of menopause, which may be exacerbated by the effects of cancer treatment and Tamoxifen.
• Prioritize regular, quality sleep, incorporate gentle exercise into your routine, and communicate openly with your healthcare provider about fatigue levels.
• Sleep Disturbances: Changes in hormone levels may impact sleep patterns, leading to difficulties falling asleep or staying asleep.
• Establish a relaxing bedtime routine, limit caffeine intake, and create a comfortable sleep environment to improve sleep quality.
• Bone Health Concerns: Lower estrogen levels can affect bone density, potentially increasing the risk of bone-related issues.
• Consume a diet rich in calcium and vitamin D, engage in weight-bearing exercises, and discuss bone health supplements with your healthcare provider.
• Weight Gain: Some women may experience weight gain, particularly around the abdominal area, as a result of hormonal changes.
• Maintain a balanced diet, engage in regular physical activity, and seek guidance from a nutritionist or healthcare provider for personalized advice.
• Memory and Concentration Issues: Menopausal symptoms can include difficulties with memory and concentration, commonly referred to as "brain fog."
• Organize tasks, use memory aids like notes or apps, and practice mindfulness techniques to enhance focus and concentration.
• Joint Pain: Joint pain or stiffness may be experienced by some women as a symptom of menopause.
• Incorporate low-impact exercises like swimming or walking into your routine, and consider consulting with a physical therapist for targeted exercises.
• Increased Risk of Osteoporosis: Reduced estrogen levels during menopause can contribute to a higher risk of developing osteoporosis, a condition characterized by weakened bones.
• Ensure an adequate intake of calcium and vitamin D, engage in weight-bearing exercises, and discuss bone health medications with your healthcare provider.
• Changes in Libido: Some women undergoing menopause may experience a decrease in sexual desire or changes in sexual function.
• Foster open communication with your partner, explore intimacy in different ways, and consult with a healthcare provider if concerns persist.

It's important to note that the severity and combination of these symptoms can vary among individuals, and not all women will experience the same set of symptoms. Having experienced most of these side effects at some point during my time on Tamoxifen, I encourage you to consult with your healthcare team for help in managing and addressing these menopausal symptoms effectively.

Other scientific studies about Tamoxifen

If you feel like getting into more details, here are some studies with additional data about Tamoxifen. You know, for light evening reading, or when you want to fall asleep more quickly…

The Long and Short of Tamoxifen Therapy: A Review of the ATLAS Trial

ATLAS study looks at the benefit of taking Tamoxifen for 10 years instead of 5 years.

Assessment of 25-Year Survival of Women With Estrogen Receptor–Positive/ERBB2-Negative Breast Cancer Treated With and Without Tamoxifen Therapy

In this secondary analysis of data from 565 postmenopausal women with lymph node–negative, estrogen receptor–positive, and ERBB2-negative breast cancer who participated in the Stockholm tamoxifen randomized clinical trial (STO-3), tumor size and tumor grade were significantly associated with long-term (25-year) survival. A significant tamoxifen treatment benefit was observed among patients with larger tumors, lower tumor grades, and progesterone receptor–positive tumors.

Supportive Tools and Services from Manta Care

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Conclusion

Hormone-positive breast cancer relies on hormones like estrogen and progesterone to grow, and doctors use medicines like Tamoxifen to block these hormones and slow down or stop the cancer. Tamoxifen can affect menstrual cycles, leading to irregular periods or stopping them altogether. We reviewed the roles of the hormones estrogen, and progesterone in the body and why blocking them with Tamoxifen impacts the menstrual cycle. We also discuss the various side effects of Tamoxifen, including menopausal symptoms, and discuss tips for managing these side effects, such as regular check-ups, open communication with healthcare providers, lifestyle modifications, and emotional support. We, at Manta Cares, are walking this path with you. Join our community for more resources and information to help you navigate your own cancer experience. And know that you are not alone in your experience. We are here to help!

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