Common and serious side effects of anastrozole

October 10, 2025 •

4 min read

In clinical trials, up to 36% of postmenopausal women taking anastrozole for early-stage breast cancer reported experiencing hot flashes and muscle or joint problems. Anastrozole, also known by the brand name Arimidex, is an aromatase inhibitor prescribed to block estrogen production, a process that can lead to various side effects. Patients must be aware of the most common side effects of anastrozole to effectively manage their treatment.

Quick Summary

Anastrozole is a hormone therapy for breast cancer in postmenopausal women. Its common side effects are tied to lower estrogen levels, including hot flashes, joint pain, fatigue, and mood changes. Long-term use can lead to bone thinning and higher cholesterol. Patients should be aware of these potential effects and work with their healthcare provider to manage them proactively.

Key Points

Joint and Muscle Pain: A frequent side effect of anastrozole, often presenting as stiffness and discomfort, particularly in the hands, knees, and back.
Hot Flashes: Similar to menopause symptoms, hot flashes and sweating are common due to the medication's estrogen-lowering effects.
Bone Health Risks: Long-term use can decrease bone density, increasing the risk of osteoporosis and fractures. Monitoring bone density and taking calcium/vitamin D supplements is often recommended.
Cardiovascular and Cholesterol Effects: Anastrozole can increase cholesterol levels and, in some cases, potentially increase cardiovascular risk, requiring regular monitoring.
Fatigue and Mood Changes: Many patients experience weakness, tiredness, and shifts in mood, including anxiety or depression.
Vaginal Dryness: Lower estrogen levels can lead to symptoms like vaginal dryness, which can be managed with topical products.
Nausea: Gastrointestinal discomfort and nausea are possible side effects, which may be mitigated by taking the medication with food.

Anastrozole, a powerful aromatase inhibitor, is a standard treatment for hormone receptor-positive breast cancer in postmenopausal women. By significantly lowering the body's estrogen levels, it can effectively prevent cancer recurrence and progression. However, this reduction in estrogen also causes a range of side effects, from common discomforts to more serious, long-term health risks. Understanding and managing these effects is a critical part of successful treatment.

Common side effects of anastrozole

Most side effects of anastrozole are a direct result of the medication's effect on estrogen and often resemble symptoms of menopause. These effects can vary in intensity and may subside over time, but they can still significantly impact a patient's quality of life. The most frequently reported issues include:

Joint and muscle pain (arthralgia): A significant number of women experience pain and stiffness in their joints, particularly in the hands, knees, ankles, and back. This often appears within the first few months of treatment. Regular, gentle exercise like walking or yoga can help improve joint mobility.
Hot flashes and night sweats: As estrogen levels drop, hot flashes—sudden feelings of heat with sweating—are a very common complaint. Patients can find relief by dressing in layers, avoiding common triggers like spicy foods and alcohol, and keeping rooms cool.
Fatigue and weakness: Feeling unusually tired or lacking energy is a common symptom. Regular exercise and a balanced diet can help improve stamina and manage fatigue.
Mood changes: Anastrozole can cause mood swings, anxiety, and depression. While these can also be related to a cancer diagnosis, it's important to discuss new or persistent mood changes with a healthcare provider.
Nausea and gastrointestinal issues: Nausea, vomiting, and stomach upset are frequently reported. Taking the medication with food can help alleviate nausea for some patients.
Vaginal dryness: The reduction in estrogen can lead to vaginal dryness and itching. Over-the-counter moisturizers and lubricants can help manage this side effect.

Long-term and serious side effects

While many side effects are manageable, anastrozole can also pose serious, long-term risks that require ongoing monitoring and management.

Osteoporosis and bone fractures

Anastrozole's role in lowering estrogen, a hormone essential for maintaining bone strength, can lead to decreased bone mineral density over time. This increases the risk of developing osteoporosis and bone fractures, particularly in the hips, spine, and wrists. Healthcare providers will often monitor a patient's bone density and recommend calcium and vitamin D supplements, regular weight-bearing exercise, or bone-strengthening medications if necessary.

Cardiovascular risks

Anastrozole can increase cholesterol levels, which elevates the risk of heart problems over the long term. This risk is especially relevant for women with a pre-existing history of ischemic heart disease. Symptoms like new or worsening chest pain and shortness of breath warrant immediate medical attention. Regular cholesterol checks are important for managing this risk.

Skin and liver reactions

Rare but serious skin reactions, including blistering or ulceration, can occur. Any unusual rash or skin change should be reported to a doctor immediately. Additionally, liver problems like hepatitis are a rare side effect, and symptoms such as jaundice (yellowing of the skin and eyes) and stomach pain should prompt immediate medical evaluation.

Comparing side effects: anastrozole vs. tamoxifen

For treating hormone-sensitive breast cancer, oncologists may prescribe either an aromatase inhibitor like anastrozole or a selective estrogen receptor modulator (SERM) like tamoxifen. While both are effective, their side effect profiles differ because of their distinct mechanisms of action.


Side Effect	Anastrozole (Aromatase Inhibitor)	Tamoxifen (SERM)
Mechanism	Blocks the enzyme aromatase, preventing estrogen production in the body.	Blocks estrogen receptors in breast tissue but acts like estrogen in other areas, such as the bones.
Hot Flashes	Very common, often more intense than with tamoxifen.	Common, but may be less frequent than with anastrozole.
Joint/Muscle Pain	Very common due to low estrogen.	Less common, as tamoxifen has estrogen-like effects on joints.
Bone Health	Can decrease bone mineral density, increasing the risk of osteoporosis and fractures.	Tends to maintain or improve bone density.
Vaginal Symptoms	Often causes vaginal dryness.	Can cause vaginal discharge and irritation.
Cardiovascular Risk	Can increase cholesterol levels, with a potential increase in heart-related risks in some patients.	May increase the risk of blood clots and stroke.

Conclusion: Navigating anastrozole side effects

Anastrozole is a vital and effective treatment for many women with hormone receptor-positive breast cancer. Its side effects, while challenging, can be managed with proactive strategies and open communication with your healthcare team. The most common side effects of anastrozole, such as joint pain and hot flashes, are often manageable with lifestyle changes or supportive medications. More serious long-term risks, like osteoporosis and cardiovascular issues, require careful monitoring. By being informed and working closely with medical professionals, patients can navigate these side effects while focusing on the therapeutic benefits of the medication. For any new or worsening symptoms, it's always best to consult your doctor for personalized advice.

For more detailed information on managing side effects of aromatase inhibitors, consult a reputable oncology patient resource like BreastCancer.org.

Frequently Asked Questions

The most common side effects of anastrozole include joint and muscle pain, fatigue, and hot flashes. In clinical studies, these effects were reported by a significant number of patients, particularly those with early-stage breast cancer.

Yes, some side effects of anastrozole can be long-term. These include decreased bone density leading to osteoporosis, elevated cholesterol levels, and potential cardiovascular risks, which typically manifest with extended treatment.

To manage joint pain, it is recommended to engage in regular, gentle exercise like walking or yoga to improve mobility. Some over-the-counter pain relievers may help, but you should always consult your doctor before taking them. Your doctor might also recommend switching to a different medication if the pain is severe.

Anastrozole may increase cholesterol levels and, in rare cases, could pose a risk for heart problems, particularly in individuals with pre-existing heart disease. Regular monitoring of cholesterol and heart health is crucial.

Weight gain is reported by some patients taking anastrozole. However, studies have shown that the rate is often similar to those taking a placebo, suggesting other factors like lifestyle or general cancer treatment may play a role. Regular exercise and a healthy diet are recommended to manage weight.

Some early side effects, like hot flashes, nausea, and headache, may decrease in intensity over the first few months as your body adjusts. However, long-term effects like osteoporosis and high cholesterol will persist as long as the medication is taken and require ongoing management.

If you experience severe side effects such as chest pain, shortness of breath, serious skin reactions, or signs of liver problems like jaundice, you should seek immediate medical attention.