Anastrozole Safety Information
Generic Name: Anastrozole Drug Class: Non-steroidal Aromatase Inhibitor Brand Reference: Arimidex
Important: At Strut Health, anastrozole is prescribed off-label for men on testosterone replacement therapy (TRT) to help manage elevated estrogen levels. The FDA-approved indication for anastrozole is the treatment of hormone receptor-positive breast cancer in postmenopausal women. The clinical trial data summarized below comes primarily from studies conducted in postmenopausal women. The safety profile in men using anastrozole for estrogen management is less established. Your prescribing provider will evaluate whether anastrozole is appropriate for you based on your individual health profile.
1. Warnings
Do not use anastrozole if you:
- Have had an allergic reaction to anastrozole or any of its inactive ingredients. Serious allergic reactions including anaphylaxis (a life-threatening whole-body reaction) and angioedema (severe swelling of the face, lips, tongue, or throat) have been reported.
Cardiovascular risk:
- In clinical trials, patients with pre-existing heart disease who took anastrozole experienced ischemic cardiovascular events (reduced blood flow to the heart) at a higher rate than those on a comparison medication (17% vs. 10%). If you have a history of heart disease, coronary artery disease, angina, or prior heart attack, make sure your prescribing provider is aware before starting this medication.
Bone health:
- Anastrozole has been associated with decreased bone mineral density and an increased rate of fractures (10% vs. 7% in clinical trials). If you have osteoporosis, osteopenia, or other risk factors for bone loss, discuss this with your provider.
Cholesterol:
- Elevated cholesterol levels were observed more frequently with anastrozole use (9% vs. 3.5% in clinical trials). Your provider may monitor your lipid levels while you are on this medication.
Pregnancy:
- Anastrozole is contraindicated during pregnancy. It can cause fetal harm. While this warning is primarily relevant for female partners, men taking anastrozole should be aware of this risk and discuss contraception planning with their provider if applicable.
Dosage and administration:
- Take anastrozole exactly as prescribed by your Strut Health provider. Do not adjust your dose or stop taking the medication without consulting your provider.
Monitoring requirements:
- Your provider may order periodic lab work to monitor your estrogen levels, cholesterol, and other relevant markers while you are on anastrozole. Attend all scheduled follow-up appointments and lab draws.
2. Before Taking This Medication
Tell your Strut Health provider if you have or have ever had any of the following:
- Heart disease, coronary artery disease, angina, or a history of heart attack or stroke
- Osteoporosis, osteopenia, or a history of bone fractures
- High cholesterol or a history of lipid abnormalities
- Liver disease or impaired liver function (anastrozole has not been studied in patients with severe hepatic impairment)
- Kidney disease
- Any history of allergic reactions to medications
Tell your provider about all medications you are currently taking, including prescription drugs, over-the-counter medications, vitamins, and supplements. See the Drug Interactions section below.
Age restriction:
Patients under 18 years of age are not eligible for this medication through Strut Health. Anastrozole is not indicated for use in pediatric patients.
3. Drug Interactions
Do not take anastrozole with the following:
- Tamoxifen -- Tamoxifen reduces anastrozole levels in the blood by 27%, and the combination provides no additional benefit. These medications should not be taken together.
- Estrogen-containing therapies -- Estrogen-based medications, supplements, or creams can counteract the effect of anastrozole, making it less effective. Do not use estrogen-containing products while taking anastrozole.
Medications that do not require adjustment:
- Warfarin (blood thinners) -- Clinical studies showed that anastrozole does not affect warfarin's blood-thinning activity. No dose adjustment is needed.
- Other CYP450-metabolized medications -- Anastrozole is unlikely to affect the levels of other medications processed through the liver's CYP450 enzyme system. However, always inform your provider of all medications you take.
4. Side Effects
a. Emergency Symptoms -- Seek Immediate Medical Attention
Call 911 or go to the nearest emergency room if you experience any of the following:
- Signs of a severe allergic reaction (anaphylaxis): difficulty breathing, swelling of the face, lips, tongue, or throat, rapid heartbeat, dizziness or fainting, severe skin rash or hives
- Signs of a heart attack: chest pain or pressure, pain radiating to the arm, jaw, or back, shortness of breath, cold sweats, nausea
- Signs of a stroke: sudden numbness or weakness on one side of the body, sudden confusion, trouble speaking, sudden severe headache, vision changes
b. Serious Side Effects -- Stop Taking and Contact Your Provider
Contact your Strut Health provider promptly if you experience any of the following
- Bone or joint pain that is severe or worsening
- Signs of a bone fracture (sudden pain, swelling, inability to bear weight)
- Severe or persistent headaches
- Significant mood changes or worsening depression
- Skin reactions such as blistering, peeling, or severe rash (Stevens-Johnson syndrome and erythema multiforme have been reported in post-marketing surveillance.)
- Signs of liver problems: yellowing of the skin or eyes, dark urine, persistent nausea, upper right abdominal pain (hepatitis and elevated liver enzymes have been reported)
- Unusual swelling in the hands, feet, or legs (peripheral edema)
- Tendon pain, swelling, or rupture (reported in post-marketing surveillance)
c. Common Side Effects
The following side effects were reported in clinical trials. Because these studies were conducted in postmenopausal women, the frequency and type of side effects in men may differ.
- Hot flashes -- 36% of patients in clinical trials
- Musculoskeletal symptoms (joint pain, stiffness, arthritis) -- 36% of patients
- Arthralgia (joint pain) -- 15%
- Weakness or fatigue -- 19%
- Hypertension (elevated blood pressure) -- 13%
- Depression -- 13%
- Nausea -- 11%
- Skin rash -- 11%
- Headache -- 10%
- Back pain -- 10%
- Insomnia -- 10%
- Swelling in hands or feet (peripheral edema) -- 10%
- Elevated cholesterol -- 9%
- Weight gain -- 9%
- Diarrhea -- 9%
- Constipation -- 8%
- Dizziness -- 8%
- Shortness of breath -- 8%
- Tingling or numbness (paresthesia) -- 7%
- Bone pain -- 7%
- Indigestion -- 7%
- Carpal tunnel syndrome -- 2.5%
If any side effect becomes bothersome or does not go away, contact your Strut Health provider.
5. Disclaimers
Off-label use:
Anastrozole is FDA-approved for the treatment of hormone receptor-positive breast cancer in postmenopausal women. At Strut Health, it is prescribed off-label for men on testosterone replacement therapy to manage elevated estrogen (estradiol) levels. Off-label prescribing is a legal and common medical practice in which a provider prescribes an FDA-approved medication for a use other than its approved indication, based on clinical evidence and professional judgment.
Clinical data limitations:
The safety data presented on this page is derived primarily from clinical trials conducted in postmenopausal women with breast cancer (the ATAC trial, median follow-up of 68 months, with over 3,000 patients per treatment arm). The safety profile of anastrozole in men using it for estrogen management has not been established through large-scale clinical trials. Your experience may differ from what is described here.
This page is not a substitute for medical advice:
This safety information is provided for educational purposes and does not replace the clinical judgment of your prescribing provider. Always follow your provider's instructions regarding dosage, monitoring, and duration of therapy. If you have questions or concerns about your medication, contact your Strut Health provider directly.
Last updated: 2026-02-13 Source: FDA-approved prescribing information for anastrozole (Arimidex)
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