Isosorbide is a nitrate medication prescribed to manage angina and certain heart conditions by widening blood vessels and improving blood flow. Whilst it plays a vital role in cardiovascular care, many men wonder whether isosorbide could help with erectile dysfunction—or whether it can be safely combined with treatments for ED. The answer is clear: isosorbide does not treat erectile dysfunction and must never be taken alongside medications such as sildenafil (Viagra) or tadalafil (Cialis), as this combination can cause a dangerous drop in blood pressure. This article explains how isosorbide works, why it is contraindicated with ED treatments, and what safe alternatives are available for men taking nitrates.

What Is Isosorbide and How Does It Work?

Isosorbide is a nitrate medication commonly prescribed to manage angina (chest pain). It belongs to a class of drugs known as organic nitrates, which work by relaxing and widening blood vessels throughout the body. The two main forms are isosorbide mononitrate and isosorbide dinitrate, both of which are converted in the body to nitric oxide—a powerful vasodilator.

When blood vessels dilate, blood flow improves and the heart's workload decreases. This mechanism is particularly beneficial for patients with coronary artery disease, as it reduces the oxygen demand of the heart muscle and helps prevent angina attacks. Isosorbide mononitrate is typically taken once or twice daily for long-term prevention, whilst isosorbide dinitrate may be used more frequently depending on the formulation.

In selected cases of chronic heart failure—for example, when ACE inhibitors or angiotensin receptor blockers cannot be tolerated—isosorbide dinitrate may be used in combination with hydralazine. Intravenous nitrates are also used in acute heart failure and acute coronary syndromes in hospital settings.

Common side effects of isosorbide include:

• Headaches (often improving after the first few days)

• Dizziness or light-headedness, particularly when standing up

• Flushing of the skin

• Low blood pressure (hypotension)

These effects occur because nitrates dilate blood vessels throughout the body, not just in the heart. To maintain effectiveness and reduce the risk of tolerance, long-term nitrate therapy is usually scheduled with a nitrate-free interval each day—typically 10–14 hours overnight—as recommended in the BNF and product information.

Patients are usually advised to take isosorbide at consistent times each day and to avoid suddenly stopping the medication, as this can lead to rebound angina. It is also important to limit alcohol intake, as alcohol can increase the blood pressure–lowering effect of nitrates. Most critically, isosorbide must never be taken alongside medications used to treat erectile dysfunction—including sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), and avanafil (Spedra)—as this combination can cause a dangerous drop in blood pressure.

If you experience side effects that concern you, report them via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Understanding how isosorbide works is essential when considering its relationship with sexual health and erectile function.

Sources: electronic Medicines Compendium (eMC) SmPCs for isosorbide mononitrate and isosorbide dinitrate; British National Formulary (BNF); NHS Medicines – Isosorbide mononitrate

Does Isosorbide Help Erectile Dysfunction?

Isosorbide does not help erectile dysfunction and must never be used for this purpose. In fact, taking isosorbide alongside medications commonly prescribed for erectile dysfunction (ED)—such as sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), or avanafil (Spedra)—is absolutely contraindicated and can cause a dangerous and potentially life-threatening drop in blood pressure.

Erectile dysfunction medications work by inhibiting an enzyme called phosphodiesterase type 5 (PDE5), which leads to increased blood flow to the penis. These drugs also enhance the effects of nitric oxide, the same chemical pathway that isosorbide activates. When nitrates like isosorbide are combined with PDE5 inhibitors, the cumulative vasodilatory effect can cause severe hypotension, leading to dizziness, fainting, heart attack, or stroke.

The Medicines and Healthcare products Regulatory Agency (MHRA) and UK prescribing guidelines explicitly state that the concurrent use of any nitrate or nitric oxide donor with any PDE5 inhibitor is contraindicated under all circumstances. This means that no PDE5 inhibitor should be taken at any time whilst you are using isosorbide or any other nitrate, regardless of timing or dosing schedule.

Some men may wonder whether the vasodilatory properties of isosorbide could theoretically improve erectile function. Whilst nitric oxide does play a role in achieving erections, isosorbide is not targeted to the penile vasculature and does not provide therapeutic benefit for ED. Moreover, cardiovascular conditions requiring nitrate therapy often coexist with erectile dysfunction, making it essential that patients discuss safe treatment alternatives with their GP rather than attempting to self-manage with inappropriate medications.

Important safety advice: If you experience chest pain during or after sexual activity and have taken a PDE5 inhibitor, do not take nitrates. Call 999 immediately and inform the paramedics or emergency department staff that you have taken an ED medication.

Sources: eMC SmPCs for sildenafil, tadalafil, vardenafil, and avanafil; BNF interaction warnings; MHRA guidance

Safe Treatment Options for Erectile Dysfunction

Men experiencing erectile dysfunction have several safe and effective treatment options available, even when taking heart medications like isosorbide. The key is to work closely with a healthcare professional to identify therapies that do not interact dangerously with nitrates.

Non-pharmacological approaches should be considered first-line for many patients:

• Lifestyle modifications: Weight loss, regular exercise, smoking cessation, and reducing alcohol intake can significantly improve erectile function and cardiovascular health

• Psychological support: Counselling or cognitive behavioural therapy (CBT) may help when ED has psychological components such as anxiety or depression

• Pelvic floor exercises: Strengthening pelvic floor muscles through physiotherapy can improve erectile function in some men

For patients who cannot use PDE5 inhibitors due to nitrate therapy, alternative medical treatments include:

• Vacuum erection devices: Mechanical pumps that draw blood into the penis, with a constriction ring maintaining the erection

• Alprostadil: Available as injections directly into the penis (intracavernosal), pellets inserted into the urethra (intraurethral), or as a cream applied to the tip of the penis (Vitaros)

• Testosterone replacement therapy: Indicated only when ED is associated with confirmed hypogonadism—symptoms of low testosterone plus consistently low morning testosterone levels on repeat blood tests

• Penile prosthesis: A surgical option for men with refractory ED who have not responded to other treatments

According to NICE guidance, management of ED should address underlying cardiovascular risk factors and any contributing medications. Some antihypertensives, antidepressants, and other drugs can worsen erectile function, and your GP may be able to adjust these. It is essential never to stop prescribed heart medications without medical supervision, as this could have serious consequences for your cardiovascular health.

Your GP will typically arrange initial investigations, which may include blood tests for testosterone (taken in the morning), HbA1c or glucose, lipid profile, and checks of blood pressure, kidney function, and thyroid function. Depending on the findings, you may be referred to a specialist—such as a urologist, endocrinologist, or cardiologist—for further assessment and management.

Sources: NICE Clinical Knowledge Summary (CKS) – Erectile dysfunction; NHS – Erectile dysfunction (treatments); BNF; British Society for Sexual Medicine (BSSM) guidance

When to Speak to Your GP About ED and Heart Medications

If you are taking isosorbide or any other nitrate medication and experiencing erectile dysfunction, it is essential to speak openly with your GP before attempting any treatment. Many men feel embarrassed discussing sexual health, but ED is a common condition affecting approximately half of men aged 40–70 to some degree, and healthcare professionals are accustomed to these conversations.

You should contact your GP if:

• You are experiencing new or worsening erectile dysfunction

• You are taking nitrates and wish to explore ED treatment options

• You have been offered or prescribed ED medication without being asked about heart medications

• You experience chest pain, dizziness, or other concerning symptoms during sexual activity

Your GP will conduct a thorough assessment, which typically includes reviewing your cardiovascular history, current medications, and any other health conditions such as diabetes or high blood pressure that may contribute to ED. They may perform blood tests to check testosterone levels (taken in the morning and repeated if low), blood glucose or HbA1c, lipid profiles, kidney function, and thyroid function. This holistic approach ensures that any treatment recommended is both safe and addresses underlying causes.

Your GP may refer you to a specialist if:

• There are signs of hormonal problems (suspected hypogonadism)

• You have Peyronie's disease or other structural abnormalities

• There are neurological signs or symptoms

• Initial treatments have failed

• You have high cardiovascular risk requiring specialist input

Important safety advice about buying medicines online: In the UK, sildenafil 50 mg (Viagra Connect) is available from pharmacies without a prescription following a pharmacist consultation. However, you should only purchase medicines from General Pharmaceutical Council (GPhC)–registered UK pharmacies. Avoid websites that supply prescription-only medicines without an appropriate UK medical assessment or valid prescription, as these may be operating illegally and selling counterfeit or unsafe products. The MHRA provides guidance on how to buy medicines safely online.

If you experience chest pain during sexual activity, stop immediately and call 999. This could indicate unstable angina or another serious cardiac event. If you have taken a PDE5 inhibitor for erectile dysfunction, inform the paramedics or emergency department staff immediately, as nitrates must not be given.

Your cardiologist and GP can work together to optimise your heart medications whilst finding safe solutions for erectile dysfunction, ensuring both your cardiovascular health and quality of life are maintained.

Sources: NICE CKS – Erectile dysfunction (assessment and management); NHS – Erectile dysfunction (when to get help); GPhC and MHRA guidance on buying medicines online

Frequently Asked Questions