What Is Arimidex? Uses, Dosage, and What You Need to Know in 2026

If you've just been prescribed Arimidex (anastrozole), you probably have a lot of questions. What exactly is it? What does it do? How do you take it, and for how long? This guide answers the most important things patients need to know about anastrozole in 2026.

What Is Arimidex?

Arimidex is the brand name of anastrozole, a non-steroidal aromatase inhibitor (AI). It is manufactured by AstraZeneca and first received FDA approval in 1995 — making it one of the most well-studied drugs in its class. Generic anastrozole has been widely available since around 2010-2012 when the patent expired.

In simple terms, anastrozole is a breast cancer medication that works by lowering estrogen levels in the body. Many breast cancers — specifically those that are "hormone receptor-positive" (ER+ or PR+) — are fueled by estrogen. By blocking estrogen production, anastrozole helps stop or slow the growth of these cancers.

What Is Arimidex Used For?

Anastrozole has three FDA-approved uses, all for postmenopausal women:

1. Adjuvant treatment of early hormone receptor-positive breast cancer. After surgery for early-stage breast cancer, anastrozole is given to reduce the risk of recurrence. Treatment typically continues for 5 to 10 years, based on individual risk factors and current ASCO guidelines.
2. First-line treatment of locally advanced or metastatic breast cancer. For postmenopausal women with hormone receptor-positive or hormone receptor-unknown locally advanced or metastatic breast cancer, anastrozole is approved as an initial treatment option.
3. Second-line treatment after tamoxifen. For women whose advanced breast cancer has progressed on tamoxifen therapy, anastrozole is an approved treatment option.

It is important to note: anastrozole is FDA-approved only for postmenopausal women. It does not provide the same benefit for premenopausal women and is not indicated for that population. Some off-label uses exist (including in male patients with gynecomastia and in ovulation induction), but these are physician-directed decisions outside the scope of this article.

What Is the Dose of Arimidex?

Anastrozole comes in one strength: 1 mg tablets. The dose is one tablet taken orally once per day. It can be taken with or without food. There is only one approved dose — you should not take more or less without your doctor's instruction.

No dose adjustment is needed for elderly patients, or for patients with renal (kidney) or mild-to-moderate hepatic (liver) impairment.

How Do I Take Arimidex?

Here are the key instructions for taking anastrozole correctly:

• Take one 1 mg tablet once per day, at the same time each day
• You may take it with or without food — food does not significantly affect the overall absorption, though the rate may slow slightly
• If you miss a dose, take it as soon as you remember. If it's almost time for your next dose, skip the missed one — do not double up
• Store at room temperature (68-77°F), away from moisture and heat
• Do not stop taking anastrozole without talking to your oncologist — even if you feel fine, the medication is actively working to reduce recurrence risk

How Long Do I Take Arimidex?

For adjuvant treatment of early breast cancer, the American Society of Clinical Oncology (ASCO) recommends using aromatase inhibitors for up to 10 years in postmenopausal patients with early-stage, node-positive, hormone receptor-positive breast cancer. In the ATAC trial, patients were treated for a median of 60 months (5 years). Your oncologist will determine the appropriate duration based on your specific diagnosis, risk factors, and how you tolerate the medication.

For advanced or metastatic breast cancer, anastrozole is continued until the cancer progresses or is no longer working.

Who Should NOT Take Arimidex?

Anastrozole is contraindicated (should not be used) in the following situations:

• Premenopausal women (it does not work the same way and is not indicated)
• Pregnancy (can cause fetal harm — women of reproductive potential must use effective contraception during therapy and for at least 3 weeks after the last dose)
• Patients with known hypersensitivity (allergy) to anastrozole or any of its ingredients
• While taking estrogen-containing products (HRT, hormonal birth control) — these directly counteract the drug's mechanism
• While taking tamoxifen — the combination reduces anastrozole blood levels by 27% and provides no added benefit

Brand vs. Generic: Is Anastrozole Different from Arimidex?

Generic anastrozole is the same active ingredient as brand-name Arimidex. By FDA standards, generics must be bioequivalent to the brand-name drug, meaning they deliver the same active ingredient in the same amount. The generic and brand will produce the same clinical effect. Most insurance plans and patients use generic anastrozole, which is dramatically less expensive.

Bottom Line

Arimidex (anastrozole) is a once-daily 1 mg tablet that treats hormone receptor-positive breast cancer in postmenopausal women by reducing estrogen levels. It's one of the most-studied breast cancer medications available, with an established safety and efficacy record going back to 1995. For a deeper dive into how it actually works at the molecular level, read our article on how Arimidex works. If you need help finding it at a pharmacy near you, medfinder.com can help.