Tadalafil and Diltiazem: Can They Be Taken Together?

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At a glance

What is tadalafil and what is diltiazem?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED) and, at lower doses, benign prostatic hyperplasia (enlarged prostate). It works by relaxing blood vessels in the penis, allowing increased blood flow during sexual stimulation. Tadalafil is available as on-demand tablets (10 mg or 20 mg, taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5 mg or 5 mg) for continuous treatment [4].

Diltiazem is a calcium-channel blocker prescribed to treat high blood pressure (hypertension), angina (chest pain caused by reduced blood flow to the heart), and certain abnormal heart rhythms. It works by relaxing and widening blood vessels, which lowers blood pressure and reduces the heart's workload. Diltiazem is usually taken once or twice daily, depending on the formulation (standard-release or modified-release).

Both medicines affect blood vessels and blood pressure, which is why their interaction needs to be understood and monitored by your prescriber.

How do tadalafil and diltiazem interact?

Tadalafil and diltiazem can be taken together, but the combination requires caution because both medicines lower blood pressure. Tadalafil relaxes blood vessels in the penis and elsewhere in the body, which can cause a modest drop in blood pressure. Diltiazem also lowers blood pressure by relaxing the walls of blood vessels throughout the body. When taken together, these effects can add up, potentially causing symptoms such as dizziness, light-headedness, fainting, or a feeling of weakness, particularly when you stand up quickly (postural hypotension) [3][4].

There is also a pharmacokinetic interaction: diltiazem is a moderate inhibitor of an enzyme called CYP3A4, which is responsible for breaking down tadalafil in the liver. This means diltiazem can slightly increase the levels of tadalafil in your bloodstream, which may enhance both the desired effects and the risk of side effects such as headache, flushing, indigestion, or nasal congestion [4][12].

This interaction is well recognised and manageable. Your prescriber will review your current blood pressure control, your dose of diltiazem, and any other medicines you take before deciding whether tadalafil is suitable and, if so, at what dose.

What will my prescriber check before prescribing tadalafil with diltiazem?

Before prescribing tadalafil to someone taking diltiazem, a UK prescriber will carry out a thorough assessment during your online or face-to-face consultation. They will ask about your current blood pressure readings, whether your blood pressure is well controlled on diltiazem, and whether you have experienced any dizziness or fainting episodes. They will also review all your other medicines to check for additional interactions, particularly with other blood-pressure-lowering drugs or medicines that affect the CYP3A4 enzyme [2][4].

Your prescriber will ask about your heart health, including any history of heart attack, stroke, unstable angina, severe heart failure, or abnormal heart rhythms. They will also check whether sexual activity is safe for you, as this is an important consideration for anyone with cardiovascular conditions [1][2]. If you are taking other medicines that lower blood pressure (such as ACE inhibitors, angiotensin receptor blockers, beta-blockers, or diuretics), the prescriber will consider the cumulative effect on your blood pressure.

If tadalafil is deemed suitable, your prescriber may start you on a lower dose (for example, 10 mg on-demand rather than 20 mg, or 2.5 mg daily rather than 5 mg) to minimise the risk of low blood pressure. They will advise you on what to watch for and when to seek help.

Starting on a lower dose

Because diltiazem can increase tadalafil levels in the blood, your prescriber may recommend starting with the lowest effective dose of tadalafil. For on-demand use, this is usually 10 mg; for daily use, 2.5 mg. This cautious approach helps to reduce the risk of side effects while still providing benefit for erectile dysfunction. Your prescriber will review how you respond and may adjust the dose if needed, always balancing effectiveness with safety [4][12].

What you need to know

• Tadalafil and diltiazem can be taken together, but both lower blood pressure so caution is needed.
• Diltiazem can slightly increase tadalafil levels, so your prescriber may start you on a lower dose.
• Watch for dizziness or light-headedness, especially when standing up quickly.
• Always declare all your medicines during your online consultation for a safe prescriber review.
• Avoid heavy alcohol and grapefruit juice while taking tadalafil with diltiazem.

What are the warning signs to watch for when taking tadalafil and diltiazem together?

If you are taking tadalafil and diltiazem together, it is important to be aware of the signs that your blood pressure may be dropping too low. Common symptoms include dizziness or light-headedness, especially when standing up quickly from sitting or lying down; feeling faint or unsteady; unusual tiredness or weakness; or a rapid or irregular heartbeat. If you experience any of these symptoms, sit or lie down immediately and avoid driving or operating machinery. Contact your GP or pharmacist for advice [1][4].

More serious warning signs that require urgent medical attention include fainting or loss of consciousness, severe dizziness that does not improve, chest pain or tightness (especially during or after sexual activity), sudden severe headache, or sudden loss of vision or hearing. If you develop an erection that lasts longer than four hours (priapism), this is a medical emergency and you should go to A&E immediately, as permanent damage can occur without prompt treatment [3][4].

It is also important to avoid drinking large amounts of alcohol when taking tadalafil, as alcohol can further lower blood pressure and worsen side effects such as dizziness and headache. Grapefruit juice should be avoided or limited, as it can increase tadalafil levels in the blood [4][12].

When to contact your GP

If you experience persistent or troublesome side effects such as headache, flushing, indigestion, or nasal congestion, speak to your GP or pharmacist. These are common side effects of tadalafil and may settle with time, but your prescriber can review your dose or suggest ways to manage them. If you notice any new symptoms after starting tadalafil, or if your blood pressure readings at home are consistently lower than usual, contact your GP for a medication review [2][4].

Practical advice for taking tadalafil with diltiazem

If your prescriber has approved tadalafil for you while you are taking diltiazem, there are several practical steps you can take to use it safely. Take tadalafil exactly as prescribed—do not take more than the recommended dose or take it more often than once a day (for on-demand use) or once a day (for daily use). Swallow the tablet whole with water; you can take it with or without food, although a very large, high-fat meal may delay the onset of effect for on-demand tablets [4].

Stand up slowly from sitting or lying positions, especially in the first few hours after taking tadalafil, to reduce the risk of dizziness. Avoid drinking excessive alcohol, as this can increase the risk of low blood pressure and make erectile dysfunction worse. Do not drink grapefruit juice regularly, as it can raise tadalafil levels in your blood [4][12].

Keep all your medicines up to date on your patient record with Cured Pharmacy and with your GP. If you are prescribed a new medicine by your GP or another healthcare provider, always mention that you are taking tadalafil and diltiazem so they can check for interactions. Never take tadalafil if you are also taking 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 [3][4].

When to get urgent help

• Fainting, severe dizziness, or loss of consciousness
• Chest pain or tightness during or after sexual activity
• An erection lasting longer than 4 hours (priapism)
• Sudden loss of vision or hearing
• Severe or persistent headache with confusion or slurred speech

Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.

Can I take other ED medicines with diltiazem?

All PDE5 inhibitors licensed for erectile dysfunction in the UK—sildenafil (Viagra), tadalafil (Cialis), vardenafil (Levitra), and avanafil (Spedra)—can interact with diltiazem in a similar way, because they all lower blood pressure and are all metabolised by the CYP3A4 enzyme to varying degrees. The same caution applies: your prescriber will assess your blood pressure control, review your other medicines, and may start you on a lower dose [3][5][6].

Vardenafil and avanafil are more sensitive to CYP3A4 inhibition than sildenafil or tadalafil, so dose adjustments or additional caution may be needed. Your prescriber will choose the most appropriate PDE5 inhibitor for you based on your individual circumstances, including how well your blood pressure is controlled, your other medical conditions, and your preferences (for example, whether you prefer an on-demand tablet or a daily low-dose option) [2][5][6].

Never take more than one PDE5 inhibitor at the same time, as this can significantly increase the risk of serious side effects, including dangerously low blood pressure. If you wish to try a different ED medicine, speak to your prescriber first—they will advise you on how to switch safely [3][4][5][6].

Choosing the right ED treatment

Your prescriber will help you choose the ED medicine that best suits your lifestyle and medical needs. Tadalafil is often preferred by men who want flexibility, as its effects can last up to 36 hours, or by those who prefer a daily low-dose tablet for spontaneity. Sildenafil and vardenafil are taken about an hour before sex, while avanafil works faster (15–30 minutes). All require sexual stimulation to work and all need prescriber approval, especially if you are taking diltiazem or other blood-pressure medicines [1][2][4].