Sildenafil and Diltiazem: Can They Be Taken Together?
Learn how these medicines interact and what your prescriber checks during your UK consultation.
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Sildenafil and Diltiazem: Understanding the Interaction
Published: 16 October 2026
Many men taking diltiazem for high blood pressure or angina wonder whether sildenafil and diltiazem can be used together safely. The good news is that this combination is not absolutely contraindicated, but it does require careful prescriber assessment because both medicines can lower blood pressure. When used together, they may add to each other's blood-pressure-lowering effects, which can occasionally cause dizziness or light-headedness, especially when standing up.
At a glance
What is diltiazem and why is it prescribed?
Diltiazem is a calcium channel blocker, a type of medicine commonly prescribed to treat high blood pressure (hypertension) and certain heart conditions such as angina (chest pain caused by reduced blood flow to the heart). It works by relaxing and widening blood vessels, which lowers blood pressure and reduces the workload on the heart. Diltiazem is also sometimes used to control abnormal heart rhythms.
Because diltiazem lowers blood pressure, it is important to consider how it might interact with other medicines that also affect blood pressure, including erectile dysfunction treatments like sildenafil. This does not mean the combination cannot be used, but it does mean your prescriber will need to review your current dose of diltiazem, how well controlled your blood pressure is, and whether you have experienced any side effects such as dizziness or fainting.
If you have been prescribed diltiazem, it is essential to declare this during any online or face-to-face consultation for erectile dysfunction treatment. Your prescriber will assess whether sildenafil (or an alternative PDE5 inhibitor) is suitable for you, and if so, which dose is safest to start with.
What is sildenafil and how does it work?
Sildenafil is the generic name for Viagra, a medicine licensed in the UK to treat erectile dysfunction. It belongs to a group of medicines called PDE5 inhibitors, which work by increasing blood flow to the penis when you are sexually aroused. Sildenafil does not cause an erection on its own; sexual stimulation is still needed for it to work [3].
Sildenafil is available in three strengths: 25 mg, 50 mg, and 100 mg. The usual starting dose is 50 mg, taken about one hour before sexual activity, and no more than once a day. Depending on how well it works and whether you experience side effects, your prescriber may adjust the dose. Sildenafil can also cause a mild, temporary drop in blood pressure, which is why it must be used cautiously alongside other blood-pressure-lowering medicines.
At Cured Pharmacy, sildenafil is available on prescription following an online consultation reviewed by a UK-registered prescriber. The consultation will ask about all your current medicines, including diltiazem, to ensure safe and effective treatment.
Can you take sildenafil and diltiazem together?
Yes, sildenafil and diltiazem can be taken together, but only under the guidance of a prescriber who has reviewed your full medical history and current medicines. Unlike some combinations that are absolutely contraindicated (such as sildenafil with nitrates, nicorandil, or riociguat), the combination of sildenafil and diltiazem is not forbidden. However, it does carry a risk of additive blood-pressure-lowering effects, which means you may be more likely to experience dizziness, light-headedness, or fainting, particularly when you stand up quickly [3].
The prescriber will check several factors before approving treatment: how well your blood pressure is controlled on diltiazem, whether you have a history of low blood pressure or fainting, and whether you are taking any other medicines that also lower blood pressure. In some cases, the prescriber may recommend starting with a lower dose of sildenafil (such as 25 mg) to minimise the risk of side effects.
It is important never to take sildenafil with nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs known as 'poppers', as these combinations can cause a dangerous drop in blood pressure. Diltiazem is not in this category, so the interaction is manageable with appropriate monitoring and dose adjustment.
How the interaction works in plain English
Both diltiazem and sildenafil relax blood vessels, though they do so through different mechanisms. Diltiazem blocks calcium channels in the walls of blood vessels, causing them to widen. Sildenafil increases the effect of a natural substance called nitric oxide, which also relaxes blood vessel walls. When both medicines are present in your system at the same time, their blood-pressure-lowering effects can add together, making a drop in blood pressure more likely. For most people, this is mild and manageable, but it is why your prescriber needs to know about diltiazem before prescribing sildenafil.
What you need to know
- Sildenafil and diltiazem can be taken together, but both lower blood pressure so prescriber review is essential.
- Your prescriber may start you on a lower sildenafil dose to reduce the risk of dizziness or light-headedness.
- Never take sildenafil with nitrates, nicorandil, or riociguat; diltiazem is not in this contraindicated group.
- Declare all current medicines during your consultation to ensure safe and effective treatment.
- Seek urgent help if you experience chest pain, an erection over four hours, or sudden vision or hearing loss.
What does your prescriber check before approving sildenafil with diltiazem?
During the online consultation at Cured Pharmacy, you will be asked to list all your current medicines, including diltiazem, and to provide details about your blood pressure and any cardiovascular conditions. The prescriber will review this information to assess whether sildenafil is safe and appropriate for you. Key factors include whether your blood pressure is well controlled, whether you have experienced dizziness or fainting on diltiazem, and whether you are taking other medicines that also lower blood pressure (such as ACE inhibitors, angiotensin receptor blockers, or diuretics).
If you are stable on diltiazem and your blood pressure is within a healthy range, the prescriber may approve sildenafil, often starting with the lowest effective dose. You may be advised to take the first dose at a time when you can sit or lie down if you feel dizzy, and to avoid sudden changes in posture. If you have a history of very low blood pressure, recent heart attack or stroke, unstable angina, or severe heart failure, sildenafil may not be suitable, and the prescriber will discuss alternative options with you [1][2].
It is also important to mention any other health conditions, such as kidney or liver problems, as these can affect how your body processes sildenafil and may require a dose adjustment. Never take sildenafil without a prescriber's approval if you are on diltiazem or any other heart or blood pressure medicine.
Practical advice for taking sildenafil and diltiazem safely
If your prescriber approves sildenafil while you are taking diltiazem, follow these practical steps to minimise the risk of side effects. Take sildenafil exactly as prescribed, usually about one hour before sexual activity, and do not exceed one dose in 24 hours. Avoid drinking large amounts of alcohol, as this can worsen erectile dysfunction and increase the risk of dizziness and low blood pressure. Grapefruit juice can raise sildenafil levels in your blood, so it is best to avoid it while using this treatment.
When you first take sildenafil, be aware of how you feel. If you experience dizziness or light-headedness, sit or lie down until it passes, and avoid driving or operating machinery until you know how the medicine affects you. Stand up slowly from sitting or lying positions, especially in the first few hours after taking the tablet. If you feel faint, unwell, or notice any chest pain during sexual activity, stop and seek medical advice immediately.
Do not stop or change your diltiazem dose without consulting your GP or cardiologist, even if you think it might be causing side effects when combined with sildenafil. Both medicines are prescribed for important reasons, and any changes should be made under medical supervision. If you have concerns about the combination, speak to your prescriber or pharmacist, who can review your treatment and suggest alternatives if needed.
What to do if you experience side effects
Common side effects of sildenafil include headache, flushing, indigestion, and nasal congestion. These are usually mild and short-lived. However, if you experience severe dizziness, fainting, or a rapid or irregular heartbeat, stop taking sildenafil and contact your GP or call NHS 111 for advice. If you develop an erection lasting more than four hours (priapism), sudden loss of vision or hearing, or chest pain during sex, seek emergency medical help by calling 999 or going to A&E immediately [3].
When to get urgent help
- Erection lasting more than 4 hours (priapism) – call 999 or go to A&E immediately
- Sudden loss of vision or hearing – stop taking sildenafil and seek emergency help
- Chest pain during sexual activity – stop, rest, and call 999 if pain does not resolve quickly
- Severe dizziness, fainting, or rapid/irregular heartbeat – contact your GP or call NHS 111 for same-day advice
Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.
Alternative ED treatments if sildenafil and diltiazem are not suitable together
If your prescriber decides that sildenafil is not the best option for you while taking diltiazem, there are several alternatives to consider. Other PDE5 inhibitors, such as tadalafil (Cialis), vardenafil (Levitra), or avanafil (Spedra), work in a similar way to sildenafil and carry the same caution regarding blood pressure interactions. However, they differ in how quickly they work and how long they last, which may suit your lifestyle better. Tadalafil, for example, can be taken as a low daily dose (2.5 mg or 5 mg) or as an on-demand tablet (10 mg or 20 mg) that can last up to 36 hours [4].
Your prescriber may also discuss non-tablet options, such as Vitaros (alprostadil cream applied to the tip of the penis) or Caverject (alprostadil injection), which work locally rather than affecting blood pressure throughout the body. These treatments are prescription-only and require training to use correctly. Eroxon is a topical gel medical device available without prescription that may be suitable for some men, though it is not a medicine and works differently from PDE5 inhibitors.
In all cases, it is important to have an open conversation with your prescriber about your current medicines, your health, and your preferences. Erectile dysfunction can be an early sign of cardiovascular disease or diabetes, so if you have not already done so, see your GP for a full health check [1][2]. Treating any underlying conditions, alongside lifestyle changes such as regular exercise, a healthy diet, reducing alcohol, and stopping smoking, can improve erectile function and overall health.
How Cured Pharmacy can help
Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering discreet, convenient access to erectile dysfunction treatments following an online consultation reviewed by a UK-registered prescriber. You can request sildenafil, tadalafil, vardenafil, or avanafil, and the prescriber will assess your suitability based on your current medicines (including diltiazem), health conditions, and any previous treatments. If approved, your medicine is dispensed by our UK pharmacy and delivered in plain, unmarked packaging. First-time customers can use code Ednew for a discount on their first order.
Take your first dose safely
When you first take sildenafil with diltiazem, choose a time when you can sit or lie down if you feel dizzy. Stand up slowly and avoid alcohol to minimise the risk of low blood pressure.
Scientific References
- NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 16 October 2026]
- National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 16 October 2026]
- Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 16 October 2026]
- Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 16 October 2026]
Information on this page is for educational purposes only and is not medical advice. Prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting or changing any medication.
Common Questions
Can I take sildenafil if I'm on diltiazem for high blood pressure?
Yes, in most cases, but only after a prescriber has reviewed your blood pressure control and current medicines. The combination can lower blood pressure further, so you may be started on a lower dose of sildenafil.
Will diltiazem make sildenafil less effective?
No, diltiazem does not reduce the effectiveness of sildenafil. However, if your blood pressure drops too much, you may feel unwell, which could affect your ability to engage in sexual activity comfortably.
What should I do if I feel dizzy after taking sildenafil with diltiazem?
Sit or lie down until the dizziness passes, and avoid standing up quickly. If dizziness is severe or persistent, contact your GP or call NHS 111 for advice.
Can I take tadalafil instead of sildenafil if I'm on diltiazem?
Tadalafil is another PDE5 inhibitor with the same blood-pressure interaction as sildenafil. Your prescriber will assess which is most suitable based on your health and preferences.
Is it safe to drink alcohol while taking sildenafil and diltiazem?
Heavy alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effects of both medicines, increasing the risk of dizziness. Limit alcohol to a small amount.
Do I need to tell my GP that I'm taking sildenafil with diltiazem?
Yes, it is good practice to inform your GP, especially if you experience any side effects or if your blood pressure control changes.
Can I take sildenafil if I'm on diltiazem and another blood pressure medicine?
Possibly, but the prescriber will need to review all your medicines together to assess the overall risk of low blood pressure. Always declare every medicine you take during the consultation.
What are the warning signs that I should stop taking sildenafil and seek help?
Seek urgent help if you experience an erection lasting more than four hours, sudden loss of vision or hearing, severe dizziness or fainting, or chest pain during sex.
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Reviewed by UK-based prescribers · Takes under 3 minutes · Discreet Packaging
Medically reviewed by
Tarun Kumar, Superintendent Pharmacist (GPhC 2233073)