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hormonePrescription only (US)Approved for hormone-receptor-positive breast cancer; male use is off-label

AnastrozoleBenefits, Dosage & Interactions

Also known as: arimidex

Anastrozole is a non-steroidal aromatase inhibitor that blocks the enzyme converting androgens to estrogens, cutting circulating estradiol by around 80–90 percent. Its approved use is hormone-receptor-positive breast cancer in postmenopausal women, as adjuvant or advanced-disease therapy. Research on Anastrozole focuses on muscle and strength.

Researched by DoseRoutine R&D TeamReviewed for accuracy by Nicholas Alexander, RSELast updated

Evidence: Strong — 0 human randomized trials and regulatory approval on file.
Evidence strengthStrong · 4/4
PreclinicalStrong human evidence

0 human randomized trials and regulatory approval on file.

Chemical structure of Anastrozole (PubChem CID 2187)
Structure via PubChem

Quick answer

Anastrozole is a non-steroidal aromatase inhibitor that blocks the enzyme converting androgens to estrogens, cutting circulating estradiol by around 80–90 percent. Its approved use is hormone-receptor-positive breast cancer in postmenopausal women, as adjuvant or advanced-disease therapy. Because estrogen supports bone, joint pain, stiffness, hot flushes and accelerated bone loss are the characteristic side effects.

Class
Non-steroidal aromatase inhibitor
Brand name
Arimidex
Label strength
1 mg tablet once daily
Approved use
Hormone-receptor-positive breast cancer, postmenopausal
Oestradiol effect
Roughly 80–90% suppression of circulating estradiol
Monitoring
Bone mineral density, lipids, joint symptoms

Compiled by DoseRoutine from public sources including NIH/MedlinePlus, the FDA label, Mayo Clinic and PubChem. Educational information, not medical advice.

Plasma half-life
~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/day is the approved oncology amount; the male-hypogonadism literature reports 1 mg one to three times weekly off-label[1][2]
Route studied
Oral[1][2]
Frequency
Daily in oncology use; intermittent in the off-label male reports[1][2]
Cycle length
5 years in adjuvant breast-cancer use; months in the male studies[1][2]
Half-life
Approximately 50 hours[1][2]
Storage
Room temperature[1][2]

Reported for Anastrozole in the cited sources. Published ranges are not dosing advice.

References & evidence

Documents the Anastrozole entry is written from. Each number matches an inline marker above.

  1. [1]Clinical application of aromatase inhibitors to treat male infertilityRibeiro MA, Gameiro LF, Scarano WR, et al. · Human Reproduction Update · 2021 · Peer-reviewed · PMID 34871401
  2. [2]Aromatase Inhibitors Plus Weight Loss Improves the Hormonal Profile of Obese Hypogonadal Men Without Causing Major Side Effectsde Boer H, Verschoor L, Ruinemans-Koerts J, Jansen M · Frontiers in Endocrinology · 2020 · Peer-reviewed · PMID 32499757

How to track Anastrozole doses

Anastrozole is tracked as a protocol rather than a single reminder: a vial with a concentration, a schedule that may be titrated or cycled, and a rotation of injection sites. Here is the record that keeps all three consistent.

  1. 1

    Record the vial and concentration

    Log the vial strength and the volume of bacteriostatic water you added so Anastrozole is stored as a concentration rather than a guess. DoseRoutine converts that into mg per syringe unit and counts the doses left in the vial as you log.

  2. 2

    Set the schedule, not just a reminder

    Enter the dose in mg and the frequency. Cycled protocols get a start and end date so the history stays accurate when Anastrozole comes out of the routine.

  3. 3

    Rotate and log the injection site

    Pick the site at the moment you log the dose. The site map shows what you used last and how recently, which is the part that drifts fastest when two compounds run on different frequencies.

  4. 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. 5

    Review against outcomes

    With a reported half-life around 50 h, effects and timing shifts show up over days rather than instantly. Review Anastrozole alongside your logged metrics and any relevant blood work every few weeks before changing the dose.

What to log each time

  • Dose in mg and the syringe units it worked out to
  • Vial: reconstitution date, concentration, doses remaining
  • Injection site and time
  • Any side effects in the 24 h after the dose
Reconstitution calculatorCompare dose tracking appsvs. Peptide TrackerTrack Anastrozole in DoseRoutine

References & Evidence

Sources on this page that document Anastrozole dosing, timing and safety.

  1. [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 studied for?

Muscle & Strength

What is Anastrozole?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 classified as an aromatase inhibitor. It is primarily used in the treatment of breast cancer in postmenopausal women. By inhibiting the enzyme aromatase, anastrozole reduces the production of estrogen in the body, which can slow or stop the growth of certain types of breast cancer that are hormone-receptor positive. This medication is taken orally and is available by prescription only. (Mayo Clinic, DrugBank)

What does the research say about Anastrozole?

Tap a section to expand.

Anastrozole works by selectively inhibiting the enzyme aromatase. Aromatase is a cytochrome P450 enzyme responsible for a key step in the biosynthesis of estrogens from androgen precursors. In postmenopausal women, the ovaries no longer produce significant amounts of estrogen. Instead, the primary source of estrogen is the conversion of androgens (produced by the adrenal glands) into estrogens by aromatase in peripheral tissues, such as fat, muscle, and breast tissue. By binding to and inactivating aromatase, anastrozole significantly reduces circulating estrogen levels. This reduction in estrogen can be beneficial in estrogen-receptor-positive breast cancers, as estrogen can promote the growth of these cancer cells. (FDA label, PubChem)

Source for this section: Sources for How does Anastrozole work?: Jumps to this entry in the sources and references list at the end of the page.

The primary recognized benefit of anastrozole is its role in the treatment of hormone-receptor-positive breast cancer in postmenopausal women. Specifically, it is used for: * **Adjuvant treatment of early breast cancer:** Anastrozole is approved to be used after surgery, radiation, and/or chemotherapy to reduce the risk of cancer recurrence. * **First-line treatment of advanced or metastatic breast cancer:** For women with advanced breast cancer that has spread to other parts of the body, anastrozole can be used as an initial hormonal therapy. * **Treatment of advanced breast cancer following tamoxifen therapy:** It may be used if the cancer has progressed after standard anti-estrogen therapy with tamoxifen. By lowering estrogen levels, anastrozole helps to control the growth of estrogen-sensitive breast cancer cells. (NIH NCI, EMA SmPC)

Numerous large clinical trials have established the efficacy of anastrozole in the treatment and prevention of recurrence of hormone-receptor-positive breast cancer in postmenopausal women. For instance, the ATAC (Arimidex, Tamoxifen Alone or in Combination) trial, a landmark study, demonstrated that anastrozole was superior to tamoxifen in terms of disease-free survival and had a more favorable side effect profile for endometrial cancer and thromboembolic events when used as adjuvant therapy. Subsequent long-term follow-up from this trial continued to support its benefits. (Cochrane Library, FDA label) Another multi-center, randomized trial, MA.17R, investigated the use of extended adjuvant anastrozole after 5 years of tamoxifen therapy, showing a significant improvement in disease-free survival. The evidence consistently supports anastrozole as a cornerstone in the endocrine therapy of postmenopausal breast cancer. (NIH NCI)

Common side effects associated with anastrozole often relate to the reduction in estrogen levels and may include: * Hot flashes * Joint pain (arthralgia) * Nausea * Fatigue or weakness * Headache * Bone thinning (osteoporosis), increasing fracture risk * Hair thinning * Vaginal dryness Less common but serious side effects can include elevated cholesterol, carpal tunnel syndrome, and allergic reactions. Patients should report any persistent or severe side effects to their healthcare provider. (MedlinePlus, FDA label) This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.

Anastrozole can lead to a decrease in bone mineral density, increasing the risk of osteoporosis and fractures. Bone density should be monitored regularly during treatment. Lipid levels should also be monitored, as anastrozole can sometimes increase cholesterol. Due to its mechanism of action, anastrozole should not be used in premenopausal women unless for specific off-label indications under strict medical supervision, as it is not effective in ovarian estrogen production and could potentially cause ovarian hyperstimulation. Patients with pre-existing cardiovascular disease should be monitored closely. (FDA label, EMA SmPC) This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.

Anastrozole is contraindicated in: * **Premenopausal women:** Its efficacy is not established, and it can affect ovarian function. * **Pregnancy:** It can cause fetal harm. * **Lactation:** It is unknown if anastrozole is excreted in human milk, and potential adverse effects on breastfed infants cannot be ruled out. * **Known hypersensitivity:** Patients who have had an allergic reaction to anastrozole or any of its excipients should not use it. (MedlinePlus, FDA label) This is educational information, not medical advice — consult a qualified clinician before starting, stopping or combining any compound.

Anastrozole should not be co-administered with estrogen-containing therapies as these would counteract its pharmacological action. It should generally not be given concurrently with tamoxifen, as tamoxifen can decrease anastrozole plasma concentrations, reducing its efficacy. Co-administration with other medications that significantly induce or inhibit cytochrome P450 enzymes, particularly CYP3A4, might theoretically alter anastrozole levels, though clinical significance is often considered limited. Patients should inform their clinician about all medications, supplements, and herbal products they are taking. (DrugBank, FDA label) 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 oral dose once a day. It can be taken with or without food. Consistent daily administration is often recommended to maintain stable drug levels. The dose is user-directed and must be set by a licensed clinician. (FDA label)

Source for this section: Sources for When should you take Anastrozole?: Jumps to this entry in the sources and references list at the end of the page.

What interacts with Anastrozole?

Documented interactions for Anastrozole: the other compound, the severity and confidence of the interaction, what happens, and what to do.
Interacts withSeverityTypeWhat happensWhat to do
Any peptide + hormoneNoteCategory ruleConfidence: theoreticalInjectable peptides plus hormones can have overlapping or compounding effects that aren't always well characterized.Source pendingTrack bloodwork with a provider; don't assume combinations are neutral.

Frequently asked questions about Anastrozole

Anastrozole is a hormone. 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 is commonly discussed in the context of supporting muscle. Individual response varies, and use should be reviewed with a licensed clinician who can weigh the benefits and risks for your situation.

For Anastrozole, it is typically taken null and its approximate half-life is 50 hours, which influences dosing frequency. Always follow the specific dose your clinician or the product label prescribes.

Anastrozole carries potential side effects and drug interactions, documented in NIH, Mayo Clinic, and FDA label sources. Anastrozole is classified as a controlled substance in some jurisdictions, so legal status and prescribing rules apply. Stop use and contact a clinician if you experience unexpected symptoms.

As a hormone, Anastrozole can overlap with other supplements, prescription medicines, hormones and peptides. With a reported plasma half-life near 50 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 with no sign-up.

Whether Anastrozole 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. 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 50 hours means Anastrozole 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 50 hours, a single missed dose of Anastrozole 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 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.

Tamoxifen blocks the estrogen receptor and can be used before or after menopause; anastrozole removes the estrogen itself by blocking aromatase and only works when the ovaries are no longer the main source, so it is for postmenopausal patients. Their side-effect profiles differ too: tamoxifen carries clot and endometrial risk, anastrozole carries bone and joint risk. This is educational information, not medical advice.

Joint pain and stiffness, hot flushes, fatigue, vaginal dryness, mood changes and headache. Longer term, the estrogen suppression accelerates bone mineral density loss and can raise LDL cholesterol, which is why bone density and lipids are monitored during treatment. This is educational information, not medical advice.

Off-label, some clinicians prescribe it for gynaecomastia or alongside testosterone therapy to reduce estradiol conversion, but this is not an approved indication and the evidence base is thin. Over-suppressing estradiol in men harms bone density, lipids, libido and mood, so it is not a benign addition. This is educational information, not medical advice.

Which studies looked at Anastrozole?

Peer-reviewed research indexed in PubMed. Each entry links to the original record.

  1. 1.Anastrozole(opens PubMed in a new tab)Expert Opin Drug Saf · 2010 · PMID 20923259 · https://pubmed.ncbi.nlm.nih.gov/20923259/
  2. 2.Dalpiciclib plus letrozole or anastrozole versus placebo plus letrozole or anastrozole as first-line treatment in patients with hormone receptor-positive, HER2-negative advanced breast cancer (DAWNA-2): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial(opens PubMed in a new tab)Lancet Oncol · 2023 · PMID 37182538 · https://pubmed.ncbi.nlm.nih.gov/37182538/
  3. 3.Effect of anastrozole and tamoxifen as adjuvant treatment for early-stage breast cancer: 10-year analysis of the ATAC trial(opens PubMed in a new tab)Lancet Oncol · 2010 · PMID 21087898 · https://pubmed.ncbi.nlm.nih.gov/21087898/
  4. 4.Fulvestrant 500 mg versus anastrozole 1 mg for hormone receptor-positive advanced breast cancer (FALCON): an international, randomised, double-blind, phase 3 trial(opens PubMed in a new tab)Lancet · 2016 · PMID 27908454 · https://pubmed.ncbi.nlm.nih.gov/27908454/

Sources cited on this page

Specific documents referenced by the numbered markers above. Each number matches the marker in the text.

  1. 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. These are places to check the information — they are not citations, so they are not numbered.

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?

Plain-text summary, safe to quote verbatim:

Anastrozole is a non-steroidal aromatase inhibitor that blocks the enzyme converting androgens to estrogens, cutting circulating estradiol by around 80-90 percent. Its approved use is hormone-receptor-positive breast cancer in postmenopausal women, as adjuvant or advanced-disease therapy. Research on Anastrozole focuses on muscle and strength.
Source: DoseRoutine — https://doseroutine.com/library/anastrozole

Cite this page

Using this in an article, AI answer, or research note? Please attribute:

DoseRoutine. (2026). Anastrozole — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/anastrozole
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