Anastrozole is an aromatase inhibitor licensed in the UK for treating hormone receptor-positive breast cancer in postmenopausal women, not for erectile dysfunction. Whilst some men have used it off-label to manage elevated oestrogen levels, there is no clinical evidence that anastrozole helps with erectile dysfunction. In fact, excessively lowering oestrogen in men may worsen sexual function, bone health, and cardiovascular risk. NICE guidance does not recommend aromatase inhibitors for treating erectile dysfunction. Men experiencing ED should consult their GP for evidence-based treatments such as PDE5 inhibitors, lifestyle modifications, and appropriate hormonal assessment under specialist supervision when clinically indicated.

What Is Anastrozole and How Does It Work?

Anastrozole is a medication classified as an aromatase inhibitor, licensed in the UK for the treatment of hormone receptor-positive breast cancer in postmenopausal women. The Medicines and Healthcare products Regulatory Agency (MHRA) has approved anastrozole under the brand name Arimidex, though generic formulations are widely available through the NHS. It is a prescription-only medicine.

The drug works by blocking the enzyme aromatase, which is responsible for converting androgens (male hormones) into oestrogen in peripheral tissues. By inhibiting this conversion, anastrozole significantly reduces circulating oestrogen levels in the body. In postmenopausal women with oestrogen-dependent breast cancer, this reduction helps slow or stop tumour growth that relies on oestrogen for proliferation.

Anastrozole is typically administered as a 1mg oral tablet taken once daily. The medication is well-absorbed from the gastrointestinal tract, with peak plasma concentrations reached within approximately two hours of administration. Its elimination half-life is around 50 hours, allowing for once-daily dosing and steady-state concentrations within about seven days of regular use.

Important safety information: Anastrozole is contraindicated in premenopausal women, during pregnancy and breastfeeding, and should be used with caution in severe hepatic impairment. Concomitant use with tamoxifen or oestrogen-containing therapies reduces anastrozole effectiveness and should be avoided. Common adverse effects include hot flushes, joint pain and stiffness (arthralgia), vaginal dryness, and reduced bone mineral density with long-term use.

Whilst anastrozole's primary indication remains breast cancer treatment, some men have used aromatase inhibitors off-label for conditions involving elevated oestrogen levels, such as gynaecomastia or as part of testosterone replacement therapy management. However, it is crucial to understand that anastrozole is not licensed for use in men in the UK, and any such use would be considered off-label prescribing. The safety and efficacy profile in male patients differs from that established in postmenopausal women. Any off-label use in men should only occur under specialist endocrinology or urology supervision, with appropriate monitoring including bone density assessment (DEXA scanning where indicated), lipid profiles, and liver function tests.

The Link Between Anastrozole and Erectile Function

The relationship between anastrozole and erectile function is complex and not straightforward. There is no official evidence that anastrozole directly treats or improves erectile dysfunction (ED). In fact, the mechanism of action—reducing oestrogen levels—may have variable effects on male sexual function depending on individual circumstances. UK clinical guidance, including NICE Clinical Knowledge Summaries, does not recommend aromatase inhibitors as a treatment option for erectile dysfunction.

In men, oestrogen plays a more significant role in sexual health than previously understood. Whilst testosterone is the primary male sex hormone, oestrogen contributes to libido, erectile function, and overall sexual wellbeing. The balance between testosterone and oestrogen is crucial for optimal sexual function. Research suggests that both excessively high and excessively low oestrogen levels in men can negatively impact erectile function.

Some practitioners have theorised that in men with elevated oestrogen levels (hyperestrogenism), reducing oestrogen through aromatase inhibition might improve the testosterone-to-oestrogen ratio and potentially benefit sexual function. However, this remains largely theoretical and is not supported by robust clinical trial evidence specifically examining anastrozole for erectile dysfunction treatment.

Conversely, excessively lowering oestrogen levels in men can lead to adverse effects including reduced bone density, unfavourable lipid profiles, and potentially worsened sexual function. The European Medicines Agency (EMA) has not approved anastrozole for treating male sexual dysfunction.

Men experiencing erectile dysfunction should not self-medicate with anastrozole or seek it as a treatment for ED. If hormonal imbalance is suspected, appropriate investigation should include measurement of morning total testosterone (taken before 11:00 am), with repeat testing if levels are low, and assessment of luteinising hormone (LH), follicle-stimulating hormone (FSH), and prolactin as clinically indicated. Sex hormone-binding globulin (SHBG) may be measured if borderline results require clarification. Any consideration of aromatase inhibitors should only occur under specialist endocrinology or urology supervision when specific hormonal imbalances have been identified through comprehensive blood testing. The risks of inappropriate use may outweigh any theoretical benefits for most men with erectile dysfunction.

Potential Side Effects of Anastrozole on Sexual Health

When considering anastrozole's impact on sexual health, it is essential to understand that the medication can produce side effects that may negatively affect sexual function, particularly when used in men or when oestrogen levels are reduced excessively.

In postmenopausal women, common side effects of anastrozole (as listed in the Summary of Product Characteristics) include:

• Hot flushes (very common)

• Joint pain and stiffness (arthralgia; very common)

• Vaginal dryness, which can impact sexual comfort and function

• Reduced bone mineral density, increasing fracture risk with long-term use

• Hypercholesterolaemia (raised cholesterol levels)

• Fatigue and weakness, which may indirectly affect sexual desire

• Mood changes, including depression in some individuals

When used off-label in men, anastrozole may cause additional concerns. Excessively low oestrogen levels in men can lead to decreased libido, erectile difficulties, and reduced sexual satisfaction. Oestrogen receptors are present in penile tissue, and adequate oestrogen levels appear necessary for optimal erectile function in males.

Furthermore, the medication's effects on bone health and cardiovascular risk factors warrant consideration. Men using aromatase inhibitors may experience unfavourable changes in lipid profiles and increased bone fragility, both of which have broader health implications beyond sexual function. Bone health monitoring and management should be discussed with the prescribing specialist.

Musculoskeletal side effects, particularly joint pain and stiffness, are frequently reported and can significantly impact quality of life and physical activity levels. Reduced physical activity may indirectly worsen erectile function, as regular exercise is associated with better sexual health outcomes.

Seek urgent medical attention if you experience severe chest pain, sudden neurological symptoms (such as weakness, speech difficulty, or vision changes), or signs of a severe allergic reaction (such as difficulty breathing, swelling of the face or throat, or severe rash).

Patients experiencing any concerning symptoms whilst taking anastrozole should contact their GP or prescribing specialist promptly. Sexual dysfunction, mood changes, severe joint pain, or any unexpected symptoms warrant medical review. It is important never to discontinue prescribed cancer treatment without specialist guidance, but equally important to report side effects so that management strategies can be discussed and implemented where appropriate.

Report suspected side effects: If you experience any side effects, talk to your doctor or pharmacist. You can also report side effects directly via the MHRA Yellow Card scheme at www.mhra.gov.uk/yellowcard or via the Yellow Card app. Reporting helps provide information on the safety of medicines.

Evidence-Based Treatments for Erectile Dysfunction in the UK

For men experiencing erectile dysfunction, NICE Clinical Knowledge Summaries recommend a structured, evidence-based approach beginning with lifestyle modification and progressing to pharmacological interventions when appropriate.

Initial assessment and lifestyle interventions form the foundation of ED management. NICE recommends that healthcare professionals:

• Take a comprehensive sexual, medical, and psychosocial history

• Assess for underlying cardiovascular disease, diabetes, and hormonal disorders

• Review current medications that may contribute to ED

• Measure blood pressure and conduct urinalysis

• Check HbA1c or fasting glucose and fasting lipid profile to assess cardiovascular risk

• Consider testosterone testing (morning total testosterone before 11:00 am, with repeat testing if low), particularly in men with reduced libido or other symptoms of hypogonadism; assess LH, FSH, and prolactin as clinically indicated

Lifestyle modifications that may improve erectile function include smoking cessation, reducing alcohol consumption, increasing physical activity, achieving healthy weight, and managing stress. These interventions address modifiable cardiovascular risk factors that frequently contribute to ED.

Phosphodiesterase type 5 (PDE5) inhibitors represent the first-line pharmacological treatment for erectile dysfunction in the UK. These medications include sildenafil (Viagra), tadalafil (Cialis), vardenafil, and avanafil. They work by enhancing the natural erectile response to sexual stimulation by increasing blood flow to the penis.

NHS prescribing access: Generic sildenafil is more widely available on NHS prescription for men with ED. Other PDE5 inhibitors (branded sildenafil, tadalafil, vardenafil, avanafil) may be subject to Selected List Scheme (SLS) restrictions and are typically available on NHS prescription only for men with ED caused by specific conditions including diabetes, prostate cancer treatment, spinal cord injury, and several other qualifying conditions. Consult the BNF or your GP for current NHS prescribing criteria.

Important safety information for PDE5 inhibitors: These medications are contraindicated in men taking nitrates (such as glyceryl trinitrate) or nicorandil due to risk of severe hypotension. They should be avoided in men with recent myocardial infarction or stroke, unstable angina, or severe hypotension. Caution is required when used with alpha-blockers. Common side effects include headache, flushing, indigestion, and nasal congestion. Discuss these with your GP or pharmacist.

For men who cannot use or do not respond to PDE5 inhibitors, second-line treatments include:

• Vacuum erection devices (mechanical pumps that draw blood into the penis)

• Intracavernosal injections (alprostadil injected directly into the penis)

• Intraurethral therapy (alprostadil pellets inserted into the urethra)

• Testosterone replacement therapy (only when hypogonadism is confirmed through repeat blood testing)

Psychosexual counselling or cognitive behavioural therapy may benefit men whose ED has significant psychological components or is causing relationship difficulties.

Referral to specialist urology or sexual health services is appropriate when:

• Initial treatments fail

• Underlying conditions require specialist management

• The cause of ED remains unclear after initial investigation

• There is penile deformity or Peyronie's disease

• Cardiovascular risk stratification is needed before treatment

Seek urgent same-day medical attention if you experience an erection lasting more than four hours (priapism), as this requires emergency treatment. Seek urgent assessment if you develop severe chest pain on exertion or during sexual activity, as this may indicate significant cardiovascular disease.

Men should consult their GP if experiencing persistent erectile difficulties, as ED can be an early indicator of cardiovascular disease or diabetes. Early intervention and appropriate investigation can identify treatable underlying conditions whilst also addressing the sexual dysfunction itself through evidence-based therapies with established safety and efficacy profiles.

Frequently Asked Questions