Faslodex vs Tamoxifen – Comparison of Side Effects & Uses

Faslodex vs Tamoxifen – detailed comparison:


It is the brand name of a medication called fulvestrant, which belongs to a group of medications named estrogen receptor antagonists or antineoplastics.

This medication works by blocking the activity of estrogen in breast tissue that stops cancer from growing.


This prescription medication is used to treat certain types of breast cancer in postmenopausal women.

For women who have not gone through menopause, this estrogen receptor antagonist is given together with palbociclib, a medicine that is used to treat advanced HER2-negative breast cancer, which has progressed or spread.


The usual recommended dose is 500 mg given as an injection into the muscle of the buttocks, every 14 days for 3 doses. Then, 500 mg should be given once a month. Do not miss any scheduled appointments.

Note – each injection must be given slowly, and can take up to 2 minutes to complete.

Side Effects and Precautions

Common side effects may include:

  • muscle pain;
  • headaches;
  • constipation;
  • joint pain;
  • loss of appetite;
  • bone pain;
  • feeling tired;
  • vomiting;
  • trouble breathing;
  • nausea;
  • a cough;
  • weakness;
  • pain where the medicine was injected;
  • hot flashes.

Rare side effects may include:

  • blood clots, including deep vein thrombosis and pulmonary embolism;
  • vaginal bleeding;
  • shortness of breath;
  • sudden chest pain;
  • abnormal liver function tests.

Pregnancy & Breastfeeding

It is not known if this estrogen receptor antagonist crosses into human milk and negatively affects the infant. You and your healthcare provider will decide if the benefits outweigh the risk of using Faslodex.

Moreover, there are no well-controlled studies conducted in humans, hence, this estrogen receptor antagonist may be used if the potential benefits to the mother outweigh the potential risks to the unborn child. However, it is recommended to avoid getting pregnant or breastfeeding a baby for at least 1 year after you stop using this estrogen receptor antagonist.

To make sure that this medication is safe for you, tell your healthcare provider if you have:

  • a blood clotting disorder;
  • liver disease;
  • a low level of platelets in the blood (thrombocytopenia);
  • a bleeding disorder.


It is a medication that can be found under the brand name of Soltamox. It belongs to a group of medications called nonsteroidal antiestrogens. It works by blocking estrogen’s effects, slowing the growth of cancer cells.


This prescription medication is used:

  • in men and women, to treat breast cancer which has spread to other parts of the body;
  • to treat breast cancer in women after they have finished early treatment;
  • to lower the chance of getting invasive breast cancer in women who had surgery;
  • to lower the chance of getting breast cancer.


The usual recommended dosage is 20–40 mg a day, taken in one or more divided doses for 5 years.

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Side Effects and Precautions

Common side effects may include:

  • weight loss;
  • vaginal discharge;
  • loss of appetite;
  • nausea;
  • hot flashes.

Rare side effects may include:

  • unusual vaginal discharge or bleeding;
  • seeing halos around lights;
  • changes in the menstrual periods;
  • eye pain;
  • a new breast lump;
  • pain in your pelvic area;
  • tunnel vision;
  • blurred vision;
  • tired feeling;
  • constipation;
  • jaundice (yellowing of the skin or eyes);
  • lack of energy;
  • clay-colored stools;
  • confusion;
  • bone pain;
  • dark urine;
  • muscle weakness;
  • increased thirst or urination;
  • upper stomach pain.

This nonsteroidal antiestrogen can increase the risk of blood clots or stroke. Call your healthcare provider at once if you have:

  • signs of a blood clot in the leg – swelling, pain, or redness in one or both legs;
  • signs of a blood clot in the lung – a sudden cough, chest pain, wheezing, coughing up blood;
  • signs of a stroke – sudden severe headache, sudden numbness or weakness, problems with balance.

To make sure that this nonsteroidal antiestrogen is safe for you, tell your healthcare provider if you have:

  • liver disease;
  • a history of blood clots;
  • if you are receiving chemotherapy or radiation;
  • a history of strokes;
  • a history of cataracts;
  • high triglycerides (a type of fat in the blood);
  • high LDL and total cholesterol.

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Drug Interactions

Many medications can interact with this nonsteroidal anti-estrogen. Tell your healthcare professional if you are using any of these medications:

  • Isoniazid (Nydrazid);
  • Bromocriptine (Parlodel);
  • Pioglitazone (Actos);
  • Cimetidine (Tagamet);
  • Rifampin (Rifadin);
  • durezol;
  • Clozaril (Clozapine);
  • Tranylcypromine (Parnate);
  • Cyclophosphamide (Cytoxan);
  • antifungals, like – terbinafine (Lamisil);
  • Letrozole (Femara);
  • medicines to treat psychiatric disorders, such as – chlorpromazine (Thorazine), aripiprazole (Abilify), perphenazine (Trilafon), or haloperidol (Haldol);
  • Methimazole (Tapazole);
  • HIV or AIDS medicines, like – ritonavir (Norvir) or delavirdine (Rescriptor);
  • Nicardipine (Cardene);
  • heart rhythm medication, like – quinidine (Quinidine) or amiodarone (Cordarone);
  • an antidepressant, like – clomipramine (Anafranil), bupropion (Wellbutrin), fluoxetine (Prozac, Sarafem), duloxetine (Cymbalta), tranylcypromine (Parnate), or sertraline (Zoloft);
  • Ropinirole (Requip);
  • anti-malaria medications, like – pyrimethamine (Daraprm), chloroquine (Aralen), or quinine (Qualaquine);
  • clonazolam;
  • Ticlopidine (Ticlid).

Pregnancy & Breastfeeding

It is not known exactly whether this nonsteroidal antiestrogen passes into breast milk or if it could negatively affect the infant. But, it may slow breast milk production.

More importantly, since it could harm the unborn baby, do not use this medication if you are pregnant. Plus, try not to get pregnant for at least two months after your treatment ends.

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Bottom Line – Faslodex vs Tamoxifen 

Faslodex (active ingredient – fulvestrant) is an anti-estrogen medication that is used to treat advanced hormone-related breast cancer in women. The medication works by blocking the actions of estrogen in the body.

Tamoxifen (brand name – Soltamox) is used to treat some types of breast cancer in women and men. It works by blocking the actions of estrogen.

According to a 2004 study that was done at the Christie Hospital and Holt Radium Institute, United Kingdom, fulvestrant had similar efficacy to tamoxifen and was well tolerated in patients with hormone receptor-positive tumors.

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