Toremifene (Fareston): Side Effects, Cost, and More

If you have metastatic hormone receptor-positive breast cancer and have gone through menopause, toremifene may be a good treatment option for you.

Toremifene is a medicine called a selective estrogen receptor modulator (SERM).

Note: Toremifene is not commonly used in the United States. Tamoxifen, a very similar drug, is used more commonly. 

See Fareston prescribing information. 

Toremifene blocks the effects of estrogen on metastatic hormone receptor-positive breast cancer cells by binding to the estrogen receptors on the cells. If toremifene is in the receptor, estrogen can’t attach to it, and the cell doesn’t receive estrogen’s signals to grow and multiply.

Toremifene will not work on hormone receptor-negative breast cancer.

Toremifene is a pill taken once per day. Most doctors recommend taking it at the same time each day.

You’ll keep taking toremifene as long as you are getting benefits from the medicine.

Like almost all breast cancer medicines, toremifene can cause side effects, some of them severe. The most common side effects of toremifene are:

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  hot flashes

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  sweating

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  nausea

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  vaginal discharge

Toremifene may also cause serious side effects, such as QT prolongation, which can cause a change in your heart’s rhythm. Tell your doctor right away if you have:

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  shortness of breath

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  chest pain

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  dizziness or fainting

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  fluttering or palpitations of the heart

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  lightheadedness that comes and goes

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  seizures

You should not take toremifene if you have a heart rhythm condition called long QT syndrome, low blood potassium levels, low blood magnesium levels, a history of blood clots, or endometrial hyperplasia, an overgrowth of the cells in the lining of the uterus.

You should not take toremifene if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Toremifene may cause damage to developing embryos. To avoid getting pregnant while taking toremifene, use an effective non-hormonal type of birth control. Ask your doctor which type of non-hormonal birth control would be best for you.

There are certain medicines, supplements, and foods you should avoid if you’re taking toremifene:

CYP3A4 inducers: These medicines decrease the effects of toremifene. Examples of CYP3A4 inducers include Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy. St. John’s wort, an herbal supplement, is also considered a CYP3A4 inducer.

CYP3A4 inhibitors: These medicines increase the effects of toremifene. Examples of CYP3A4 inhibitors include Nizoral (chemical name: ketoconazole) and Sporanox (chemical name: itraconazole), which are used to treat fungal infections; Reyataz (chemical name: atazanavir), used to treat HIV; and nefazodone, used to treat depression.

Thiazide diuretics: These medicines, commonly used to treat high blood pressure, increase the risk of higher-than-normal blood calcium levels. Since toremifene can increase blood calcium levels (hypercalcemia), thiazide diuretics should be avoided during treatment. Examples of thiazide diuretics include Zaroxolyn (chemical name: metolazone), Microzide (chemical name: chlorthalidone), and Lozol (chemical name: indapamide).

Medicines known to prolong the QT interval: Because toremifene can also prolong the QT interval, medicines that further increase this risk should be avoided. Examples of medicines known to prolong the QT interval include quinidine, used to treat malaria; Pacerone (chemical name: amiodarone), used to treat an irregular heartbeat; Mellaril (chemical name: thioridazine), used to treat schizophrenia; Effexor (chemical name: venlafaxine), used to treat depression and anxiety disorders; erythromycin, an antibiotic; and Zofran (chemical name: ondansetron), used to prevent nausea and vomiting.

Grapefruit juice and grapefruit: Grapefruit can increase the effects of toremifene.

Toremifene and tamoxifen are both SERMs that have similar effectiveness. If you’re experiencing intolerable side effects on tamoxifen, your doctor may recommend you switch to toremifene.  

Community members share their experience making the switch:

“I had intolerable fatigue on tamoxifen, but switched to toremifene and it has been just fine! I wouldn't say zero side effects (occasional hot/cold flashes, irregular periods, and possible accelerated perimenopause, needing more adjustments on some psych meds to accommodate hormonal changes), but completely tolerable. I stuck out tamoxifen for about 8 months, IIRC, and now it's been over 2 years on the toremifene. My initial plan was hormone treatment for 5 years, but I will ask my doc to stay on it for as long as the side effects stay this level.” — salamandra

“I took Fareston for approximately 5 years. I found side effects were much fewer and less severe than when I was on Tamoxifen.  Weight gain was the worst SE on Fareston, but I also experienced some hair thinning.” — every8thwoman

“I'm on Fareston after being on Tamoxifen and no longer have the joint pain and overall body aches (yay!) But I'm now having spotting more and more frequently.” — NWArtLady

Read more in our toremifine discussion forum.

The cost of toremifene may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use. 

Note: Your insurance company may require you to get prior authorization before covering toremifene.

Learn more about financial assistance and medicine cost-lowering tips.