Methylene blue is a prescription-only medicine licensed in the UK for treating methaemoglobinaemia, a rare blood disorder. Some online sources suggest it may help with erectile dysfunction, but this claim lacks clinical evidence and contradicts the drug's known pharmacology. Methylene blue inhibits the nitric oxide pathway essential for achieving erections, meaning it would theoretically worsen rather than improve erectile function. This article examines the evidence, explains why methylene blue is not an appropriate treatment for erectile dysfunction, and outlines safe, proven alternatives available through the NHS.

What Is Methylene Blue and How Does It Work?

Methylene blue (methylthioninium chloride) is a synthetic compound that has been used in medicine for over a century. Originally developed as a textile dye, it was one of the first synthetic medications and has found various clinical applications. In the UK, methylene blue is a prescription-only medicine primarily licensed by the MHRA for treating acquired methaemoglobinaemia, a rare blood disorder where haemoglobin cannot effectively release oxygen to body tissues. The licensed product, Proveblue, is administered by injection under specialist supervision. Some uses of methylene blue as a diagnostic dye during surgical procedures may be off-label depending on the specific product and indication.

The pharmacological mechanism of methylene blue is complex. At therapeutic doses, it acts as an electron donor and acceptor in cellular processes. Importantly, methylene blue inhibits soluble guanylate cyclase, an enzyme that mediates the effects of nitric oxide (NO) in smooth muscle cells. By blocking this enzyme, methylene blue reduces cyclic GMP (cGMP) levels, which typically leads to vasoconstriction rather than vasodilation. At higher concentrations, it can also inhibit nitric oxide synthase, further reducing NO signalling. Additionally, methylene blue is a potent inhibitor of monoamine oxidase A (MAO-A), which has significant implications for drug interactions.

Some researchers have investigated methylene blue for conditions beyond its licensed indication, including cognitive function, neuroprotection, and antimicrobial properties. However, these investigational uses remain largely experimental, lack robust clinical evidence, and are not supported by regulatory approval in the UK. Patients should be aware that methylene blue is available only on prescription for specific licensed indications and should not purchase unlicensed products online, as these may be unsafe, of poor quality, or lack regulatory oversight.

Does Methylene Blue Help with Erectile Dysfunction?

The question of whether methylene blue helps with erectile dysfunction (ED) stems from limited laboratory and animal studies conducted primarily in the 1990s and early 2000s. Some experimental research explored methylene blue's effects on the nitric oxide pathway, which plays a central role in achieving and maintaining erections. Nitric oxide causes smooth muscle relaxation in penile blood vessels by activating soluble guanylate cyclase and increasing cGMP levels, allowing increased blood flow necessary for erectile function.

However, methylene blue's pharmacology would be expected to impair, not improve, erectile function. Because methylene blue inhibits soluble guanylate cyclase and can also inhibit nitric oxide synthase, it reduces the NO–cGMP signalling pathway that is essential for penile smooth muscle relaxation and erection. In other words, the drug's mechanism of action opposes the physiological processes required for normal erectile function.

There is no official link or established clinical evidence supporting methylene blue as an effective treatment for erectile dysfunction in humans. No large-scale, randomised controlled trials have demonstrated that methylene blue improves erectile function, and it is not licensed or recommended by NICE, the MHRA, NHS, or any major medical body for treating ED. The theoretical mechanisms explored in laboratory settings have not translated into proven therapeutic benefits in clinical practice.

Currently, evidence-based treatments for erectile dysfunction in the UK include phosphodiesterase-5 (PDE5) inhibitors such as sildenafil, tadalafil, and vardenafil, which have undergone extensive clinical testing and regulatory approval. These medications work by enhancing the effects of nitric oxide, thereby improving blood flow to the penis. It is important to note that PDE5 inhibitors are contraindicated in patients taking nitrates (including nicorandil) or riociguat due to the risk of severe hypotension, and caution is required when used alongside alpha-blockers. Other established treatments for ED include vacuum erection devices, intracavernosal injections, intraurethral therapy, and psychological or relationship therapies where appropriate.

Patients experiencing erectile dysfunction should not self-prescribe methylene blue or use it off-label for this purpose. The lack of clinical evidence, combined with its pharmacological profile and potential safety concerns, makes it an inappropriate and potentially harmful choice for ED management. Instead, individuals should consult their GP to discuss proven, safe treatment options tailored to their specific circumstances and underlying health conditions.

Safety Considerations and Potential Side Effects

Methylene blue carries several important safety considerations that patients and healthcare professionals must understand. When used at therapeutic doses for its licensed indication, it is generally well-tolerated under medical supervision, but it can cause a range of adverse effects. Common side effects include blue or green discolouration of urine, which is harmless but can be alarming if unexpected. Patients may also experience nausea, vomiting, abdominal pain, dizziness, headache, and confusion. At higher doses or with prolonged use, more serious effects can occur, including chest pain, difficulty breathing, changes in mental status, and paradoxically, methaemoglobinaemia or haemolysis.

One of the most significant safety concerns with methylene blue involves its interaction with serotonergic medications. Methylene blue is a potent inhibitor of monoamine oxidase A (MAO-A), which means it can precipitate serotonin syndrome when combined with antidepressants such as selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants, monoamine oxidase inhibitors (MAOIs), or other serotonergic drugs including tramadol, linezolid, triptans, and St John's wort. Serotonin syndrome is a potentially life-threatening condition characterised by agitation, confusion, rapid heart rate, high blood pressure, dilated pupils, muscle rigidity, and hyperthermia. The MHRA has issued specific warnings about this interaction.

Methylene blue is contraindicated in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency, as it can trigger severe haemolytic anaemia in these individuals. It is also contraindicated in pregnancy except in life-threatening circumstances where the benefit clearly outweighs the risk, and should be avoided during breastfeeding unless the benefit justifies potential risk to the infant. The drug should be used with extreme caution in patients with renal impairment, as reduced clearance can lead to accumulation and toxicity.

If you experience any side effects while taking methylene blue, you should report them to your doctor or pharmacist. You can also report suspected side effects directly via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or search for 'MHRA Yellow Card' in the Google Play or Apple App Store.

Given these safety considerations, methylene blue should only be used under medical supervision for its approved indication. Self-medication or off-label use, particularly for conditions like erectile dysfunction where no evidence supports its efficacy and its mechanism would be expected to worsen the condition, poses unnecessary and potentially serious risks. Patients considering any treatment for ED should have a thorough medical assessment to identify underlying causes and contraindications to various treatment options.

When to Speak with Your GP About Erectile Dysfunction

Erectile dysfunction is a common condition affecting men of all ages, though prevalence increases with age. It is defined as the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance. Whilst occasional difficulties with erections are normal and not necessarily cause for concern, persistent problems warrant medical evaluation. You should speak with your GP about erectile dysfunction if:

• You experience persistent or recurrent difficulty achieving or maintaining erections over a period of several weeks or months

• Erectile problems are causing you distress, anxiety, or affecting your relationships

• You notice a sudden change in erectile function

• You experience other symptoms alongside ED, such as reduced libido, difficulty with ejaculation, or pain

• You have underlying health conditions such as diabetes, cardiovascular disease, or high blood pressure

• You are taking medications that might contribute to erectile problems

Seek urgent medical attention (same-day GP appointment or emergency care) if you experience:

• An erection lasting more than four hours (priapism), which requires emergency treatment to prevent permanent damage

• Sudden severe penile pain, curvature, or deformity suggestive of Peyronie's disease or penile trauma

• New focal neurological symptoms (such as weakness, numbness, or loss of bladder/bowel control)

• Chest pain on exertion, which may indicate cardiovascular disease requiring urgent assessment

Erectile dysfunction can be an early warning sign of cardiovascular disease, as the blood vessels supplying the penis are smaller than coronary arteries and may show signs of atherosclerosis earlier. NICE guidance emphasises the importance of cardiovascular risk assessment in men presenting with ED. Your GP will typically conduct a thorough medical history, including questions about your sexual function, psychological wellbeing, relationship factors, and general health. They may perform a physical examination and arrange blood tests to check for conditions such as diabetes (HbA1c or fasting glucose), lipid abnormalities, and hormonal imbalances. Morning total testosterone levels are commonly measured, with repeat testing if initial results are borderline.

Your GP may refer you to a specialist if there is suspected endocrine disorder, failure of first-line therapy, severe Peyronie's disease, or complex underlying causes requiring specialist input from urology, andrology, or endocrinology services. Psychosexual therapy may be recommended where psychological or relationship factors are significant.

It is important to be open and honest with your GP about erectile difficulties. Many men feel embarrassed discussing sexual health, but GPs are experienced in managing these concerns professionally and confidentially. Early consultation allows for identification of underlying causes, appropriate investigation, and access to evidence-based treatments. Your GP can discuss the range of effective treatment options available, including lifestyle modifications, psychological support, and pharmacological therapies, helping you find an approach that suits your individual circumstances and preferences.

Frequently Asked Questions