Sildenafil Contraindications Guide

What are the contraindications for sildenafil?

Sildenafil (also known by the brand name Viagra) is one of the most widely used medications for erectile dysfunction. 

Its popularity is due to sildenafil’s effectiveness in helping men with ED to achieve and maintain an erection. 

While it is highly effective and generally well tolerated, its contraindications must be known to ensure safe use.

Sildenafil contraindications include any known allergies, health conditions, or other medications that could cause harm when taken with sildenafil medication. 

Contraindications range in severity from potentially life-threatening (absolute contraindications) to precautions (relative contraindications). 

The Patient Information Leaflet provides a complete list of what you need to know before taking sildenafil medication.

Our guide to Everything You Need to Know About Sildenafil also answers frequently asked questions, such as ‘who can and cannot take sildenafil?’. 

Contraindications could cause a life-threatening situation, so you must not take sildenafil in any of the following events.

1. You’re allergic to sildenafil or any of the medication’s ingredients

2. You’re taking any kind of nitrates or nitric oxide donors

3. You’re taking riociguat

4. You have a severe heart or liver problem

5. You have a rare eye disease (e.g., NAION)

What are the relative contraindications for sildenafil?

Relative contraindications mean you must take precautions, as you could be at a high risk of experiencing interactions. If any of the following apply to you, only take sildenafil if your GP or pharmacist deems it safe.

1. You have sickle cell anaemia, leukaemia, or multiple myeloma 

2. You have a deformity of your penis or Peyronie’s Disease

3. You have problems with your heart

4. You currently have a stomach ulcer or a bleeding problem 

5. You have kidney or liver problems

Relative contraindications do not mean that you can not take sildenafil. Your GP or pharmacist can start you on a lower dose depending on your circumstances. We always recommend speaking to a GP before you dismiss sildenafil as a possible treatment. 

The lowest dose of sildenafil for treating ED is 25mg. This starting dosage is often prescribed to patients with health conditions or those who are prone to side effects.

For more information on dosages, read our Sildenafil Dosage Guide.

What medication should not be taken with sildenafil?

Medications that should not be taken with sildenafil include:

• Nitrates - Nitrates, often prescribed for chest pain (angina), can cause a severe drop in blood pressure when combined with sildenafil. Examples include nitroglycerin and isosorbide mononitrate.

• Riociguat - This medication, used for pulmonary hypertension, can also cause a dangerous drop in blood pressure when taken with sildenafil.

• Protease inhibitors - Commonly used in HIV treatment, these can increase the levels of sildenafil in the blood, leading to an increased risk of side effects.

• Alpha-blockers - Used for high blood pressure or prostate problems, alpha-blockers can also cause a significant drop in blood pressure when taken with sildenafil.

• Other PDE5 Inhibitors - Taking multiple medications for erectile dysfunction can increase the risk of side effects and complications.

• Any other oral or local treatments for erectile dysfunction, or pulmonary arterial hypertension medicines 

• Certain antifungal medicines

Please inform your GP or pharmacist if you’re taking any of these medications.

Why should I avoid alcohol?

Alcohol is known to make it harder for men to keep and maintain an erection, which is why it's best avoided if you have erectile dysfunction.

The best way to take sildenafil is on its own, without food or alcohol. 

The reason for this is that food and alcohol can affect how long it takes the medication to work and can lead to delays in onset time. 

You should also avoid grapefruit juice as this is known to cause an interaction.

What are the specific side effects of sildenafil that I should be aware of?

Common side effects of sildenafil you should be aware of include headaches, nausea, blocked nose, and dizziness. 

Our guide to adjusting to ED medication has advice on managing the most common side effects of sildenafil.

Rare side effects of sildenafil include chest pains, prolonged or painful erections, sudden loss of vision, severe skin reaction, and fits (seizures).

If you experience any rare side effects, stop taking sildenafil and call 999 straight away.

How can I determine if I am allergic to sildenafil or its ingredients?

If you're concerned about being allergic to sildenafil or any of its ingredients, your GP can review your medical history and discuss any previous allergies to medications you have had.

If you are known to be sensitive to similar drugs, specifically PDE5 inhibitors, your GP can assess the risk.

You could also speak to your GP about taking an allergy test.

What steps should I take if I experience side effects after taking sildenafil?

If you experience any side effects, you must report them to your GP or pharmacist.

You may need a lower dose or an alternative medication to sildenafil, such as Cialis (tadalafil) and vardenafil.

If your symptoms are severe, rare, or life-threatening, then you must ring 999.

Where can I find more information about sildenafil?

You can find out more information about erectile dysfunction on our Health Hub or Online Doctor pages.

If you’re ready to speak to one of our online clinicians about your eligibility for sildenafil, you can start a free consultation today. 

Pricing details for privately prescribed items are also available on the sildenafil treatments page.

Advice and information to help erectile dysfunction