medicationPrescription only (US)Anastrozole (Arimidex) is FDA-approved as an aromatase inhibitor for hormone receptor-positive breast cancer in postmenopausal womenUse in men or for non-oncologic purposes such as fertility or bodybuilding-adjacent estrogen control is off-label and not supported by the cited oncology trials
Anastrozole (Arimidex)Benefits, Dosage & Interactions
Also known as: Arimidex
Anastrozole, sold under the brand name Arimidex among others, is a medication primarily used in the treatment of breast cancer in postmenopausal women. It belongs to a class of drugs known as aromatase inhibitors. The reported plasma half-life is about 46 hours, which shapes dosing frequency.
Researched by DoseRoutine R&D TeamReviewed for accuracy by Nicholas Alexander, RSELast updated
Evidence: Strong — 2 human randomized trials and regulatory approval on file.
Evidence strengthStrong · 4/4
PreclinicalStrong human evidence
2 human randomized trials and regulatory approval on file.
Plasma half-life
46–50 h
Default unit
mg
What published protocols report
Ranges documented in the literature, shown for reference. DoseRoutine does not recommend an amount — your prescriber or the product label sets the dose.
- Reported amounts
- 1 mg once daily in both the IBIS-II breast-cancer prevention trial and the FALCON advanced-breast-cancer trial[1][2][3]
Reported for Anastrozole (Arimidex) in the cited sources. Published ranges are not dosing advice.
References & evidence
Documents the Anastrozole (Arimidex) entry is written from. Each number matches an inline marker above.
- [1]AnastrozoleKelly CM, Buzdar AU · Expert Opinion on Drug Safety · 2010 · Peer-reviewed · PMID 20923259
- [2]Use of anastrozole for breast cancer prevention (IBIS-II): long-term results of a randomised controlled trialCuzick J, Sestak I, Forbes JF, Dowsett M, Cawthorn S, Mansel RE · Lancet · 2020 · Peer-reviewed · PMID 31839281
- [3]Fulvestrant 500 mg versus anastrozole 1 mg for hormone receptor-positive advanced breast cancer (FALCON): an international, randomised, double-blind, phase 3 trialRobertson JFR, Bondarenko IM, Trishkina E, Dvorkin M, Panasci L, Manikhas A · Lancet · 2016 · Peer-reviewed · PMID 27908454
How to track Anastrozole (Arimidex) doses
Tracking Anastrozole (Arimidex) well takes four fields and a habit. Here is what to record so the log is still useful in three months.
- 1
Add the dose and unit
Log Anastrozole (Arimidex) with its dose in mg so totals stay comparable over time — including days when you split the dose or skip it.
- 2
Set the time of day and food rule
Pick the time you actually take it. Reminders fire at that time and can export to your calendar.
- 3
Check it against the rest of the stack
Run Anastrozole (Arimidex) through the interaction checker against everything else in the routine — supplements, peptides, hormones and prescriptions — before it becomes a daily habit.
- 4
Log adherence, not intentions
Mark each dose taken, skipped or delayed as it happens. Weeks of honest logs are what make an adherence rate or a trend line meaningful; retrospective guessing is not.
- 5
Review against outcomes
With a reported half-life around 46 h, effects and timing shifts show up over days rather than instantly. Review Anastrozole (Arimidex) alongside your logged metrics and any relevant blood work every few weeks before changing the dose.
What to log each time
- Dose in mg
- Time of day
- Taken / skipped / delayed
- Any side effects or notable changes
References & Evidence
Sources on this page that document Anastrozole (Arimidex) dosing, timing and safety.
- [1]National Center for Biotechnology Information View source
Educational information only — not medical advice. Dose ranges vary by person, indication and prescriber.
What is Anastrozole (Arimidex)?Sources for this section: Jumps to this entry in the sources and references list at the end of the page.
Anastrozole, sold under the brand name Arimidex among others, is a medication primarily used in the treatment of breast cancer in postmenopausal women. It belongs to a class of drugs known as aromatase inhibitors. Aromatase is an enzyme in the body that converts androgens (male hormones) into estrogens (female hormones). By inhibiting this enzyme, anastrozole reduces the total amount of estrogen in the body, which can slow or stop the growth of certain types of breast cancer that are sensitive to estrogen. The half-life of anastrozole is approximately 48 hours, meaning it takes about two days for half of the drug to be eliminated from the body. It is typically taken orally. Anastrozole is not a controlled substance but is a prescription-only medication.
What does the research say about Anastrozole (Arimidex)?
Tap a section to expand.
Anastrozole functions as a selective non-steroidal aromatase inhibitor (NSAI). Its primary mechanism of action involves reversibly binding to the aromatase enzyme, thereby preventing the conversion of adrenal androgens, such as androstenedione, to estrogens, specifically estrone, and subsequently estradiol. In postmenopausal women, the principal source of estrogen is via the aromatase enzyme, which is found in various tissues including fat, muscle, liver, and breast tissue. By significantly reducing circulating estrogen levels, anastrozole deprives estrogen-receptor-positive breast cancer cells of the estrogen needed for their growth and proliferation. This targeted reduction in estrogen is crucial for its efficacy in hormone-sensitive breast cancers. Studies described in FDA labels show anastrozole can reduce circulating estradiol levels by over 80%.
Source for this section: Sources for How does Anastrozole (Arimidex) work?: Jumps to this entry in the sources and references list at the end of the page.
The primary medical benefit of anastrozole is in the treatment of hormone receptor-positive breast cancer in postmenopausal women. Specific benefits include:
* **Adjuvant Treatment of Early Breast Cancer:** Anastrozole is used as an adjuvant therapy for early-stage, localized breast cancer that is hormone receptor-positive. It aims to reduce the risk of recurrence following initial treatments like surgery and/or radiation. Clinical trials cited in its FDA label have demonstrated anastrozole's effectiveness in improving disease-free survival compared to other endocrine therapies in this setting.
* **First-Line Treatment of Advanced Breast Cancer:** For postmenopausal women with advanced or metastatic hormone receptor-positive breast cancer, anastrozole may be used as a first-line treatment. By lowering estrogen levels, it can help to control tumor growth and progression.
* **Second-Line Treatment of Advanced Breast Cancer:** It is also indicated for women with advanced breast cancer that has progressed despite treatment with tamoxifen or other anti-estrogen therapies. In these cases, anastrozole offers an alternative mechanism to continue suppressing estrogen-driven cancer growth.
While occasionally discussed in non-medical contexts for other purposes, its established and approved medical benefits are strictly within the realm of breast cancer treatment, as detailed by sources like DrugBank and the FDA.
The efficacy of anastrozole in treating hormone receptor-positive breast cancer is well-supported by extensive clinical trial data and has led to its approval by regulatory bodies worldwide, including the FDA and EMA. Key evidence includes:
* **ATAC (Arimidex, Tamoxifen Alone or in Combination) Trial:** This large, randomized, double-blind study (referenced in its FDA label and many oncology guidelines) compared anastrozole, tamoxifen, and their combination as adjuvant therapy for postmenopausal women with early breast cancer. The trial demonstrated that anastrozole was superior to tamoxifen in improving disease-free survival and reducing the incidence of contralateral breast cancer, with a better safety profile for serious adverse events. Long-term follow-up further confirmed these benefits.
* **Meta-analyses and Systematic Reviews:** Multiple meta-analyses by groups like Cochrane have synthesized data from various trials, consistently showing anastrozole's effectiveness in reducing recurrence risk and improving survival outcomes in the indicated patient population. These analyses underscore its role as a standard of care in endocrine therapy for breast cancer.
* **Pharmacodynamic Studies:** Studies detailed by PubChem and DrugBank characterize its potent and selective inhibition of the aromatase enzyme, leading to significant and sustained reductions in circulating estrogen levels, which is the biological basis for its therapeutic effect.
The use of anastrozole is rigorously evidence-based within its approved indications.
Anastrozole can cause a range of side effects, as it significantly lowers estrogen levels, which can impact various bodily systems. These side effects are generally well-documented in FDA labels and clinical literature.
Commonly reported side effects include:
* Hot flashes
* Joint pain (arthralgia)
* Nausea
* Fatigue or weakness
* Headache
* Bone pain
* Increased sweating
* Hair thinning
* Vaginal dryness
* Rash
* Weight gain
Less common but potentially more serious side effects may include:
* **Osteoporosis and bone fractures:** Due to prolonged estrogen suppression, anastrozole can lead to bone density loss. Regular monitoring of bone mineral density may be recommended.
* **Cardiovascular events:** There may be an increased risk of ischemic cardiovascular events, such as angina or myocardial infarction, though this risk is generally balanced against the benefits in cancer treatment.
* **Elevated cholesterol levels:** Anastrozole can increase total cholesterol and LDL (bad) cholesterol levels.
* **Liver enzyme elevations:** While usually asymptomatic, liver function tests may show abnormal results.
* **Vaginal bleeding:** New or persistent vaginal bleeding should be reported to a clinician immediately, as it can be a sign of a serious condition.
* **Allergic reactions:** Rarely, severe allergic reactions such as angioedema or anaphylaxis can occur.
Individual experiences with side effects can vary greatly. This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Certain warnings and precautions are important to consider when using anastrozole, as outlined in official prescribing information from sources like the FDA and EMA.
* **Bone Mineral Density (BMD):** Anastrozole can cause a decrease in BMD, leading to an increased risk of osteoporosis and fractures. Patients should have their BMD assessed before starting treatment and regularly monitored thereafter. Strategies to mitigate bone loss, such as calcium and vitamin D supplementation or bisphosphonate therapy, might be discussed with a clinician.
* **Cardiovascular Risk:** Anastrozole has been associated with an increased incidence of ischemic cardiovascular events in some studies. Patients with pre-existing cardiovascular disease should be carefully monitored.
* **Cholesterol Levels:** Increases in total cholesterol and LDL cholesterol have been observed. Clinicians may recommend monitoring lipid profiles.
* **Liver Impairment:** Anastrozole is metabolized in the liver. While no dose adjustment is generally needed for mild to moderate hepatic impairment, caution should be exercised in patients with severe impairment.
* **Kidney Impairment:** No dose adjustment is typically required for renal impairment, but caution is advised in patients with severe renal compromise.
* **Pregnancy and Lactation:** Anastrozole is contraindicated in pregnant women as it can cause fetal harm. It is also not recommended for use during lactation.
* **Premenopausal Women:** Anastrozole is not indicated for use in premenopausal women. Aromatase inhibitors are less effective in premenopausal women because of suppression of ovarian estrogen synthesis. Premenopausal women should have their postmenopausal status confirmed prior to initiating therapy.
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Anastrozole is contraindicated in several situations to ensure patient safety and optimize treatment outcomes, as detailed in its official prescribing information.
* **Pregnancy:** Anastrozole is contraindicated in pregnant women, as animal studies and its mechanism of action suggest a high potential for fetal harm. It is classified as Pregnancy Category D by the FDA.
* **Lactation (Breastfeeding):** It is contraindicated in breastfeeding women due to the potential for serious adverse reactions in the nursing infant, though it is not known whether anastrozole is excreted in human milk.
* **Known Hypersensitivity:** Individuals with a known hypersensitivity or allergic reaction to anastrozole or any of its excipients should not use this medication.
* **Premenopausal Women:** Anastrozole is generally contraindicated in premenopausal women with hormone receptor-positive breast cancer, as its efficacy is primarily established in postmenopausal women, and it may not be effective in the presence of functioning ovaries. Status should be confirmed before treatment.
This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Mixing anastrozole with certain other medications can lead to altered drug effectiveness or increased risks of side effects. Key interactions are highlighted in drug information from sources like DrugBank and FDA labels.
* **Estrogen-containing Medications:** Anastrozole should not be co-administered with estrogen-containing therapies, including hormonal contraception, hormone replacement therapy (HRT), or other estrogen supplements. Estrogens directly counteract the estrogen-lowering effect of anastrozole, rendering it ineffective.
* **Tamoxifen:** Concomitant use of anastrozole with tamoxifen is not recommended. Data from the ATAC trial indicated that the combination did not show improved efficacy compared to anastrozole alone and was associated with an increased incidence of adverse events (e.g., thromboembolic events, endometrial cancer).
* **Other Aromatase Inhibitors:** Combining anastrozole with other aromatase inhibitors (e.g., letrozole, exemestane) is generally not done, as there is no demonstrated additional benefit and it could increase the risk of side effects.
Always inform your healthcare provider about all medications, supplements, and herbal products you are taking to identify potential interactions. This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.
Anastrozole is typically taken as a single dose once a day, with no specific requirement regarding meal times. It can be taken with or without food. The consistency of daily administration is more important than the exact time or food consumed. Consistent timing helps maintain stable blood levels of the medication. The dose is user-directed and must be set by a licensed clinician.
Source for this section: Sources for When should you take Anastrozole (Arimidex)?: Jumps to this entry in the sources and references list at the end of the page.
What interacts with Anastrozole (Arimidex)?
| Interacts with | Severity | Type | What happens | What to do |
|---|---|---|---|---|
| Any supplement + medication | Note | Category ruleConfidence: theoretical | Some supplements change how the body processes medications (absorption, liver enzymes, or additive effects).Source pending | Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist. |
| Any vitamin + medication | Note | Category ruleConfidence: theoretical | Certain vitamins interact with specific medications (e.g., vitamin K with blood thinners).Source pending | Specific pairs are checked against a licensed source; confirm with your provider. |
| Testosterone (TRT) | Complementary | Compound pairConfidence: theoretical | Aromatase inhibitor controls estradiol conversion from exogenous testosterone.Source pending | Dose AI to target mid-range E2; over-suppression harms joints, mood, and lipids. |
| Testosterone Cypionate | Complementary | Compound pairConfidence: theoretical | AI manages estradiol on TRT.Source pending | Titrate AI to target mid-range E2 with bloodwork every 6–8 weeks. |
Frequently asked questions about Anastrozole (Arimidex)
Anastrozole (Arimidex) is a medication. It is also known as Arimidex. The references summarized come from NIH and PubMed records, FDA labeling where it exists, and Mayo Clinic patient material.
Anastrozole (Arimidex) is commonly discussed in the context of the goals discussed on its profile page. Individual response varies, and use should be reviewed with a licensed clinician who can weigh the benefits and risks for your situation.
For Anastrozole (Arimidex), it is typically taken null and its approximate half-life is 46 hours, which influences dosing frequency. Always follow the specific dose your clinician or the product label prescribes.
Anastrozole (Arimidex) carries potential side effects and drug interactions, documented in NIH, Mayo Clinic, and FDA label sources. Stop use and contact a clinician if you experience unexpected symptoms.
As a medication, Anastrozole (Arimidex) can overlap with other supplements, prescription medicines, hormones and peptides. With a reported plasma half-life near 46 hours, separating doses can change the picture as much as removing one. Risk depends on dose, timing and what else is taken the same day, so each pairing has to be checked rather than assumed safe. The free checker at https://doseroutine.com/interaction-checker covers Anastrozole (Arimidex) with no sign-up.
Whether Anastrozole (Arimidex) fits alongside testosterone replacement therapy depends on the protocol — dose, ester and ancillaries such as HCG or anastrozole — and on current bloodwork. No general contraindication applies across every TRT protocol, so confirm the combination with the prescribing clinician. See the free TRT interaction reference: https://doseroutine.com/trt-supplement-interactions
"Peptides" is not one category — healing peptides, GLP-1 agonists, growth-hormone secretagogues and melanocortins each behave differently next to Anastrozole (Arimidex). Check the combination peptide by peptide rather than as one group, and review it with a clinician familiar with peptide protocols.
A long plasma half-life of about 46 hours means Anastrozole (Arimidex) is commonly dosed every few days or weekly rather than daily. Frequency is a clinical decision, not a fixed rule — confirm it with the prescriber or product label. Comparison of apps that keep a schedule like this: https://doseroutine.com/best-dose-tracking-apps
With a plasma half-life near 46 hours, a single missed dose of Anastrozole (Arimidex) usually has a smaller effect on overall exposure than an irregular pattern of missed doses does. Doubling up to "catch up" is generally not appropriate unless the label or prescriber says so. Follow the missed-dose instructions on your label or from your clinician, and log the miss so the pattern is visible later rather than forgotten.
For Anastrozole (Arimidex) the useful record is the dose, the time it was actually taken, and what else was taken in the same window. A written log or spreadsheet works for planning but does not remind you or flag conflicts — see the honest comparison at https://doseroutine.com/vs/spreadsheet and the wider roundup at https://doseroutine.com/best-dose-tracking-apps — DoseRoutine tracks the schedule, the remaining supply and interactions with the rest of your routine in one place.
Which studies looked at Anastrozole (Arimidex)?
Peer-reviewed research indexed in PubMed. Each entry links to the original record.
- 1.Anastrozole (Arimidex)(opens PubMed in a new tab)Clin J Oncol Nurs · 2004 · PMID 14983769 · https://pubmed.ncbi.nlm.nih.gov/14983769/
- 2.Pharmacological and clinical profile of anastrozole(opens PubMed in a new tab)Breast Cancer Res Treat · 1998 · PMID 9797018 · https://pubmed.ncbi.nlm.nih.gov/9797018/
- 3.Anastrozole (Arimidex) in clinical practice versus the old 'gold standard', tamoxifen(opens PubMed in a new tab)Expert Rev Anticancer Ther · 2002 · PMID 12503208 · https://pubmed.ncbi.nlm.nih.gov/12503208/
Sources cited on this page
Specific documents referenced by the numbered markers above. Each number matches the marker in the text.
- PubChem CID 2187(opens in a new tab)National Center for Biotechnology Information · pubchem.ncbi.nlm.nih.gov/compound/2187
Verify at
Publisher search links for Anastrozole (Arimidex). These are places to check the information — they are not citations, so they are not numbered.
- FDA-approved labeling (DailyMed)(publisher search, opens in a new tab)U.S. Food and Drug Administration · publisher search
- DrugBank(publisher search, opens in a new tab)DrugBank Online · publisher search
- Cochrane Library(publisher search, opens in a new tab)Cochrane · publisher search
- European Medicines Agency(publisher search, opens in a new tab)European Medicines Agency · publisher search
- PubMed literature search(publisher search, opens in a new tab)National Library of Medicine · publisher search
- Wikipedia entry(publisher search, opens in a new tab)Wikipedia · publisher search
DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician. How we source and review this information.
What is the short answer on Anastrozole (Arimidex)?
Plain-text summary, safe to quote verbatim:
Anastrozole, sold under the brand name Arimidex among others, is a medication primarily used in the treatment of breast cancer in postmenopausal women. It belongs to a class of drugs known as aromatase inhibitors. The reported plasma half-life is about 46 hours, which shapes dosing frequency.
Source: DoseRoutine — https://doseroutine.com/library/anastrozole-arimidex
Cite this page
Using this in an article, AI answer, or research note? Please attribute:
DoseRoutine. (2026). Anastrozole (Arimidex) — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/anastrozole-arimidex
What compounds are similar to Anastrozole (Arimidex)?
Others in the medication category or studied for the same goals.