Tamoxifen (Nolvadex) is a selective oestrogen receptor modulator licensed in the UK for breast cancer treatment. Whilst it can increase testosterone levels in men by blocking negative feedback at the hypothalamic-pituitary axis, there is no clinical evidence that tamoxifen helps with erectile dysfunction. It is neither licensed nor indicated for treating ED in the UK. Erectile dysfunction during hormone therapy often has multiple causes, including psychological distress, vascular changes, and medication side effects. Evidence-based treatments such as PDE5 inhibitors, lifestyle modifications, and psychological support remain the recommended approaches for managing ED.

What Is Tamoxifen and How Does It Work?

Tamoxifen (generic name for Nolvadex) is a selective oestrogen receptor modulator (SERM) licensed in the UK for the treatment of breast cancer. It works by blocking oestrogen receptors in certain tissues, particularly breast tissue, whilst paradoxically acting as an oestrogen agonist in other areas such as bone and the endometrium.

The mechanism of action involves competitive inhibition at oestrogen receptors. In breast tissue, tamoxifen prevents oestrogen from binding to cancer cells, thereby slowing or stopping their growth. This makes it particularly valuable in oestrogen receptor-positive breast cancers. The standard dose is 20 mg once daily, taken orally. Higher doses (40 mg) should be divided into two doses. Treatment duration often extends five to ten years depending on individual risk factors.

Whilst tamoxifen is primarily prescribed for breast cancer treatment, it is also recommended by NICE (though not licensed) for risk reduction in some high-risk women. It has been used off-label in specialist settings for male fertility treatment and to manage gynaecomastia. In men, tamoxifen can increase testosterone levels by blocking negative feedback at the hypothalamic-pituitary axis, which theoretically could influence sexual function. However, it is important to note that tamoxifen is not licensed or indicated for the treatment of erectile dysfunction in the UK.

Common adverse effects include hot flushes, nausea, and fatigue. More serious but rare complications include thromboembolic events (blood clots) and, in people with a uterus, endometrial changes. Patients should report any unusual symptoms promptly to their healthcare provider, including visual disturbances, unexplained vaginal bleeding, leg swelling/pain, or chest pain. Strong CYP2D6 inhibitors (such as paroxetine or fluoxetine) may reduce tamoxifen's effectiveness. Suspected side effects should be reported via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Why Erectile Dysfunction Occurs During Hormone Therapy

Erectile dysfunction (ED) is a recognised complication of various hormone therapies, particularly those used in cancer treatment. Understanding the underlying mechanisms helps patients and clinicians address this sensitive issue more effectively.

Androgen deprivation therapy (ADT), commonly used in prostate cancer management, is a frequent cause of ED. By suppressing testosterone production, ADT directly impacts libido, erectile function, and overall sexual satisfaction. Testosterone plays a crucial role in maintaining nitric oxide pathways essential for penile blood flow and erection.

In the context of breast cancer treatment in men (though rare), or when tamoxifen is used for other indications, the hormonal effects can be complex. Whilst tamoxifen may increase serum testosterone levels in some men through its anti-oestrogenic effects on the hypothalamus, there is no established clinical evidence that it improves erectile function. The relationship between oestrogen, testosterone, and erectile function is multifactorial and not fully understood.

Other contributing factors during cancer treatment include:

• Psychological distress – anxiety, depression, and body image concerns

• Fatigue and general ill health associated with cancer and its treatment

• Vascular changes – particularly from pelvic radiotherapy, which has stronger associations with ED than most chemotherapy

• Medication side effects from analgesics, antidepressants, or antihypertensives

It is essential to recognise that ED during hormone therapy often has multiple overlapping causes rather than a single mechanism. A holistic assessment considering physical, psychological, and relationship factors provides the best foundation for effective management. This should include cardiovascular risk assessment, as ED can be an early marker of cardiovascular disease.

Evidence-Based Treatments for Erectile Dysfunction

The management of erectile dysfunction should follow NICE guidance and be tailored to individual circumstances, underlying causes, and patient preferences. There is currently no evidence supporting tamoxifen as a treatment for ED, and it should not be used for this indication.

First-line pharmacological treatment typically involves phosphodiesterase type 5 (PDE5) inhibitors, which include:

• Sildenafil (Viagra) – usually 50 mg, taken approximately one hour before sexual activity

• Tadalafil (Cialis) – available as on-demand (10–20 mg) or daily low-dose (2.5–5 mg) formulations

• Vardenafil (Levitra) – 10 mg, taken 25–60 minutes before activity

These medications work by enhancing nitric oxide-mediated smooth muscle relaxation in the corpus cavernosum, facilitating increased blood flow during sexual stimulation. They are generally well-tolerated but contraindicated in patients taking nitrates or riociguat due to the risk of severe hypotension. Caution is needed with alpha-blockers and in significant cardiovascular disease. Sexual stimulation is required for these medications to work, and they should not be taken more than once daily.

For men who cannot use or do not respond to PDE5 inhibitors, alternative options include:

• Vacuum erection devices – mechanical aids that draw blood into the penis

• Intracavernosal injections (alprostadil) – directly administered into the penis

• Intraurethral therapy – alprostadil pellets inserted into the urethra

• Topical alprostadil cream (Vitaros) – applied to the tip of the penis

• Penile prosthesis – surgical implants for refractory cases

Psychological interventions play a vital role, particularly when anxiety, depression, or relationship difficulties contribute to ED. Cognitive behavioural therapy (CBT) and psychosexual counselling, available through NHS services or specialist clinics, can be highly effective either alone or combined with medical treatments.

Lifestyle modifications should not be overlooked. Evidence supports the benefits of regular exercise (150 minutes weekly), maintaining healthy weight, reducing alcohol consumption (within UK CMO guidelines), stopping smoking, and managing cardiovascular risk factors. These interventions improve both erectile function and overall health outcomes.

Testosterone therapy is not indicated for ED unless biochemical hypogonadism is confirmed through appropriate testing. Seek urgent medical attention for erections lasting more than 4 hours (priapism), chest pain, or sudden vision/hearing loss.

When to Speak with Your GP About Sexual Health

Discussing erectile dysfunction (persistent difficulty attaining or maintaining an erection sufficient for satisfactory sexual activity for around 3 months) can feel uncomfortable, but it is a common medical concern that GPs are well-equipped to address. Early consultation enables proper assessment, identification of underlying causes, and access to effective treatments.

You should contact your GP if:

• Erectile difficulties persist for more than a few weeks or are worsening

• ED is causing significant distress or affecting your relationship

• You experience sudden onset of erectile problems, which may indicate vascular issues

• ED is accompanied by other symptoms such as reduced libido, fatigue, mood changes, or urinary problems

• You have cardiovascular risk factors (diabetes, hypertension, high cholesterol) as ED can be an early marker of heart disease

Seek urgent medical attention if you experience:

• An erection lasting more than 4 hours (priapism)

• Chest pain or shortness of breath during or after sexual activity

• Sudden leg swelling, redness or pain (possible blood clot)

• New neurological symptoms

Your GP will typically conduct a comprehensive assessment including medical history, medication review, lifestyle factors, and psychological wellbeing. Physical examination may include blood pressure, cardiovascular assessment, and examination of genitalia. Blood tests often check testosterone levels (ideally taken between 9-11am and repeated if low), glucose, lipids, and thyroid function to identify treatable underlying conditions.

If you are currently taking tamoxifen or other hormone therapies, inform your GP as this context is important for management decisions. Whilst tamoxifen is not generally considered a direct cause of ED, the underlying condition being treated and concurrent medications may be relevant.

Referral to specialist services may be appropriate if:

• First-line treatments are ineffective or contraindicated

• There are complex hormonal or endocrine issues

• Psychological factors require specialist input

• Surgical options are being considered

Remember that sexual health is an integral part of overall wellbeing. NHS services, including sexual health clinics and specialist erectile dysfunction services, provide confidential, non-judgemental support. Early intervention typically leads to better outcomes, so do not delay seeking help if erectile dysfunction is affecting your quality of life.

Frequently Asked Questions