Hormone Therapy Drugs

Hormone Therapy Drugs

Also called: Hormone Blocking Agents, Hormone Antagonists

Reviewed By:
Martin E. Liebling, M.D., FACP


Hormone therapy is used to treat certain cancers that depend on hormones to grow and spread. Patients who undergo this treatment may use hormone therapy drugs as a form of cancer treatment. These drugs work to reduce the levels of certain hormones, such as estrogen (in women) and testosterone (in men) and prevent cancer from receiving the hormones necessary to grow.

Hormone therapy drugs may be used in both men and women with hormone-sensitive cancers, which include:

  • Breast cancer
  • Ovarian cancer
  • Uterine cancer
  • Prostate cancer

Cancer patients may be prescribed hormone therapy drugs in combination with other treatments such as chemotherapy or radiation therapy. Hormone therapy drugs also may be prescribed as treatment following surgery. These drugs are considered an effective way of preventing hormone-receptive cancers from returning and new hormone-receptive cancers from developing.

Hormone therapy drugs can cause side effects, including hot flashes, mood swings and decreased sexual desire.  In addition, some cancers become resistant to the drug and begin to grow again after a period of time.

Hormone therapy drugs are just one form of administering hormone therapy. Surgery (e.g. ovary or testicle removal) and radiation to certain reproductive organs and glands are also types of hormone therapy used to treat certain cancers.

About hormone therapy drugs

Hormone therapy drugs are used to treat forms of cancer that are influenced by certain hormones to grow and spread. These cancers are hormone-sensitive and can occur in both men and women. Biopsy and additional testing can determine if a patient’s cancer is hormone receptor positive and may benefit from hormone therapy drug treatment.

Hormone therapy medications work in one of two ways:

  • Reduce the level of hormones in the body. As these medications cause levels of hormones such as estrogen or testosterone to fall, the stimulus for cancer growth decreases.
  • Prevent cancer from using hormones. Synthetic hormones can bind to the cancer’s hormone receptors. This prevents the cancer from binding with the natural hormones it needs to thrive.

Hormone therapy drugs are often used as part of cancer treatment with certain cancers. However, they also may be used to help prevent some cancers, such as breast cancer, in high-risk women. While hormone therapy drugs can be a potent weapon in the fight against cancer, they also may cause side effects ranging from the relatively minor (nausea or tiredness) to the potentially more serious (endometrial cancer). In addition, many cancers develop resistance to hormone therapy drugs over a period of time. Because of these factors, patients should remain under close continued observation by a physician if they are receiving hormone therapy.

Types and differences of hormone therapy

Various medications are used in hormone therapy to alter a person’s levels of estrogen, progesteroneor testosterone, or to prevent cancer cells from binding with hormones. These drugs can be taken orally or by injection, and include:

  • Hormone-blocking agents. Block the ability of cancer cells to bind with hormones that stimulate the growth of certain cancers. They include:
    • Anti-estrogens. Generally given to women to block cancer cells from using estrogen stimulation. However, certain anti-estrogens have been found to block estrogen in some organs, and to act like the hormone in other organs. These are known as selected estrogen receptor modulators (SERMs) or “designer estrogens.” Anti-estrogens include tamoxifen (Nolvadex), toremifene (Fareston) and raloxifene (Evista).

      Estrogen-receptor down regulators (ERDs) are another type of anti-estrogen drug used in hormone therapy. This drug breaks down estrogen receptors and act to slow down the growth of hormone-sensitive cancers. ERDs destroy estrogen receptors and do not act like hormones elsewhere in the body. In the United States, the only ERD approved by the Food and Drug Administration (FDA) is fulvestrant (Faslodex). It is given by injection and approved for treatment of postmenopausal women with certain forms of breast cancer. It is often used after other anti-estrogen drugs or aromatase inhibitors are no longer effective.

    • Anti-androgens. Given to men to block prostate cells from activation by testosterone from the testicles and the adrenal glands. They are taken in pill form, either once a day or several times daily. They may or may not cause the loss of sex drive. They are usually used in combination with agents that block pituitary stimulation of the testicles, which do not cause the loss of sex drive. Anti-androgens include flutamide (Eulexin), bicalutamide (Casodex) and nilutamide (Nilandron).

  • Aromatase inhibitors (AIs). Block enzymes that produce estrogen. Given to postmenopausal women, they are taken in pill form once daily. This limits the amount of estrogen in the body that can be used by cancer to grow and spread. In postmenopausal women, most estrogen in the body no longer comes from the ovaries. Instead, it is produced from the hormone androgen, which is produced in the adrenal glands. Aromatase inhibitors block an enzyme in the body from turning androgen into estrogen. Aromatase inhibitors include letrozole (Femara), anastrozole (Arimidex) and exemestane (Aromasin).

    Research in clinical trials has shown that aromatase inhibitors are more effective than tamoxifen in postmenopausal women with early-stage breast cancer that is hormone receptor positive. In most women, this drug is taken for up to five years but it may be taken for a longer period of time.

  • Luteinizing hormone releasing hormone (LHRH) agonists and antagonists. Alter mechanisms in the brain that tell the body to produce hormones. This lowers hormone levels in the body. They are given by injection. These drugs serve as an alternative to surgical removal of the ovaries in women and testicles in men. In most cases, the effects of these drugs are reversible after the patient stops taking them. Abarelix (Plenaxis) is an LHRH antagonist. LHRH agonists include leuprolide (Lupron, Viadur, Eligard), goserelin acetate (Zoladex) and trelstar (Trelstar).

There are several options for treatment with hormone therapy drugs. Oncologists consider several factors in choosing a drug for a cancer patient. For example, in women, physicians will consider whether she is pre- or postmenopausal. Research has suggested that tamoxifen is the best for premenopausal women whereas aromatase inhibitors appear to be better for postmenopausal women.

In addition, other research has shown that combining or switching drugs in treatment may be more effective.

One study published in 2003 found that women who switched from tamoxifen to an aromatase inhibitor before the end of the standard five years of treatment had lower recurrence of their breast cancer. In another study released in 2005, the National Cancer Institute (NCI) reported the results of a large clinical trial in which women took an aromatase inhibitor following their course of treatment with tamoxifen. The study suggested that survival rates for women with early stage breast cancer improved with the use of an aromatase inhibitor following tamoxifen. Additional research continues on the long-term effects of hormone therapy drugs and their effectiveness in battling cancer.

Patients should discuss the benefits and risks of hormone therapy drugs with their oncologists to determine the best treatment option. After patients are placed on hormone therapy drugs, they will be monitored by their physicians and treatment may change based on individual factors.

Potential side effects of hormone therapy drugs

The side effects from hormone therapy drugs vary with the type of drug. However, common side effects found with hormone therapy drugs, including:

  • Hot flashes
  • Mood swings
  • Vaginal problems (e.g. dryness, discharge)
  • Erectile dysfunction
  • Decreased sexual desire (both sexes)
  • Fatigue and reduced energy
  • Nausea and vomiting
  • Weight gain
  • Loss of bone mass and strength (osteoporosis)
  • Thinning of hair and nails
  • Mild anemia
  • Liver problems

In addition, women who take tamoxifen may be at higher risk for endometriosis, endometrial cancer and fertility problems. They may also develop thrombosis (blood clots) and have a slightly higher risk of suffering a stroke.

In some cases, patients who take hormone therapy drugs over a long period of time may find that their cancers develop resistance to the medication. For this reason, some drugs may be given for a period of time, discontinued, and started again at a later date.  This schedule is used in the hope of preventing the development of such resistance. If resistance occurs, the patient may be switched to a new hormone therapy medication.

Recent research has indicated that changing drug treatments for women with breast cancer may reduce the risk of recurrence of the disease. In clinical trials, postmenopausal women who switched from five years of an anti-estrogen drug to an aromatase inhibitor demonstrated a lower risk of recurrent breast cancer. Other research has suggested that switching during the five-year standard treatment with tamoxifen may benefit certain breast cancer patients as well. Additional research is needed to confirm the findings of these studies.

Drug or other interactions

Patients who are using hormone therapy drugs should consult their physician before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications. For example, the combination of some anticoagulants with certain hormone therapy drugs may cause a significant increase in anticoagulation effect. Other drugs, such as diuretics, may increase the risk of clotting. Use of some hormone therapy drugs with estrogens may prevent the hormone therapy drug from working properly. 

Women who are pregnant or nursing are generally not advised to take hormone therapy drugs. In addition, some drugs may not be good for patients with various health conditions. Patients should always consult with their physician about all medication and lifestyle conditions (including alcohol and tobacco use) that might affect the use of hormone therapy drugs.

Ongoing research

A significant amount of research has been conducted in the area of hormone therapy drugs. Clinical trials and studies have focused on the following:

  • Optimal length of time for drug usage.

  • Use of aromatase inhibitors before or after a standard course of treatment with an anti-estrogen drug (tamoxifen) to reduce the risk of breast cancer recurrence.

  • Use of alternating or intermittent hormone therapy to reduce hormone therapy resistance, as is used to treat prostate cancer.

  • Use of hormone drugs to shrink tumors before therapy.

  • Timing of hormone therapy with radiation and chemotherapy.

  • Genetic effects on hormone therapy. Recent studies have shown that women with a common gene mutation affecting an enzyme may not experience the beneficial effects of tamoxifen to prevent breast cancer recurrence.

  • Treatments to reduce the side effects associated with hormone therapy drugs.

  • Use of hormone therapy to prevent breast cancer in women with an increased risk for the disease.

  • Development of vaccines with anti-androgen therapy for prostate cancer treatment.

Clinical trials are being conducted in many areas of hormone therapy. A patient’s physician can best determine if he or she is a candidate for a clinical trial.

Questions for your doctor about HT drugs

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about hormone therapy drugs:

  1. Am I a candidate for hormone drug treatment?

  2. How will it work on my cancer?

  3. What is the best type of drug for me?

  4. What are the benefits and risks associated with this drug?

  5. How do I know if the drug is working?

  6. How effective are the drugs in preventing a recurrence of my cancer?

  7. What are the side effects of the drugs?

  8. What can I do to reduce the side effects of the drugs?

  9. Should I undergo any medical tests to monitor my health while taking these drugs?

  10. Will the drugs affect my sexual function and/or fertility?

  11. How long will I have to use the drugs?

  12. Will my drugs be changed during the course of treatment?

  13. Are there any medications or supplements that could interfere with these drugs?

  14. Am I a candidate for any clinical trials?
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