Tadalafil and Entacapone: Can They Be Taken Together?

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Key takeaways

• No major direct interaction is commonly reported between tadalafil and entacapone.
• Both medicines can lower blood pressure; your prescriber checks this is safe for you.
• Stand up slowly to avoid dizziness, especially after your first tadalafil dose.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers.
• Declare all your medicines during your online consultation for a safe prescription.

What is tadalafil and how does it work?

Tadalafil is a medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused [4]. Tadalafil is the active ingredient in branded Cialis and is also available as a generic medicine.

Tadalafil comes in two forms: on-demand tablets (usually 10mg or 20mg) taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours, and daily tablets (2.5mg or 5mg) taken once a day at the same time [4]. Both forms require sexual stimulation to work—tadalafil does not cause an automatic erection.

Because tadalafil can lower blood pressure slightly, it is important that your prescriber knows about all your medicines and health conditions before you start treatment [4]. At Cured Pharmacy, every prescription is reviewed by a UK-registered prescriber after an online consultation to ensure it is safe and suitable for you.

What is entacapone and why is it prescribed?

Entacapone is a medicine used alongside levodopa and a dopa-decarboxylase inhibitor (such as carbidopa or benserazide) to treat Parkinson's disease [12]. It belongs to a class of medicines called COMT inhibitors, which work by blocking an enzyme that breaks down levodopa, helping more levodopa reach the brain and improving control of movement symptoms.

Entacapone is typically prescribed when levodopa alone is not providing consistent symptom control throughout the day, particularly when patients experience 'wearing-off' periods where symptoms return before the next dose is due [12]. Common brand names include Comtess and Comtan.

Like many Parkinson's medicines, entacapone can affect blood pressure and may cause dizziness or fainting, especially when standing up quickly [12]. This is an important consideration when assessing whether other medicines that also affect blood pressure—such as tadalafil—are suitable for you.

At a glance

How do tadalafil and entacapone interact?

No major direct drug interaction between tadalafil and entacapone is commonly reported in standard references [2][4]. Entacapone works primarily by inhibiting the COMT enzyme, which is not involved in the metabolism or action of tadalafil. Tadalafil is mainly broken down by liver enzymes called CYP3A4, and entacapone does not significantly affect this pathway [4][12].

However, both medicines can lower blood pressure, and this additive effect is the main consideration when they are used together. Entacapone, especially when combined with levodopa, may cause orthostatic hypotension (a sudden drop in blood pressure when standing), and tadalafil can also cause a mild reduction in blood pressure [4][12]. If both effects occur together, you may feel dizzy or lightheaded.

Your prescriber will assess your overall blood pressure control, how well you tolerate your Parkinson's medicines, and whether you have experienced dizziness or fainting. If tadalafil is suitable, you will usually be advised to start on the lowest effective dose and to be cautious when standing up, especially after taking your first dose [4]. It is essential to declare all your current medicines during your consultation so that your prescriber can make a fully informed decision.

The mechanism in plain English

Think of blood pressure as the force pushing blood through your arteries. Entacapone (via levodopa) and tadalafil can both relax blood vessels or reduce the force of the heart's pumping, leading to a lower pressure. When used together, these effects can add up. For most people this is manageable, but if your blood pressure drops too much, you might feel dizzy, especially when you stand up quickly. Your prescriber checks your blood pressure history and current readings to ensure the combination is safe for you.

What does your prescriber check before approving tadalafil and entacapone together?

During your online consultation at Cured Pharmacy, the prescriber will ask detailed questions about your current medicines, including the dose and frequency of entacapone and any other Parkinson's medications you take [2][4]. They will also ask about your blood pressure, whether you have experienced dizziness or fainting, and any history of heart or circulation problems.

The prescriber will check that you are not taking any medicines that are contraindicated with tadalafil—such as nitrates (GTN spray, isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called 'poppers' [4]. These combinations can cause a dangerous drop in blood pressure and must never be used together.

If you are on other blood-pressure medicines (such as alpha-blockers like tamsulosin, or antihypertensives), the prescriber will assess whether your blood pressure is stable and whether a lower starting dose of tadalafil is needed [4]. They may also advise monitoring for dizziness and adjusting the dose if necessary. The consultation ensures that tadalafil is both safe and likely to be effective for you, taking into account your full medical picture.

Practical advice for taking tadalafil with entacapone

If your prescriber approves tadalafil, take it exactly as directed. For on-demand tadalafil (10mg or 20mg), take the tablet at least 30 minutes before planned sexual activity; the effect can last up to 36 hours, so you do not need to rush [4]. For daily tadalafil (2.5mg or 5mg), take one tablet at the same time each day, regardless of when you plan to have sex.

Be especially careful when standing up from sitting or lying down, particularly after taking your first dose of tadalafil or if you have recently adjusted your entacapone or levodopa dose [4][12]. Stand up slowly and steady yourself to reduce the risk of dizziness or falls. Avoid heavy alcohol, as it can worsen erectile dysfunction and add to the blood-pressure-lowering effect of both medicines [4].

Do not take more than one dose of on-demand tadalafil in 24 hours, and do not take tadalafil if you are also using another PDE5 inhibitor (such as sildenafil or vardenafil) [4]. If you experience severe dizziness, fainting, chest pain during sex, or an erection lasting more than four hours, seek urgent medical help. Always keep your GP and Parkinson's specialist informed about all the medicines you are taking, including those for erectile dysfunction.

Tips for managing your medicines

Keep a written or electronic list of all your medicines, including doses and timings, and share it with every healthcare professional you see. This helps avoid missed interactions and ensures coordinated care. If you notice new symptoms—such as increased dizziness, worsening Parkinson's symptoms, or side effects from tadalafil—contact your prescriber or GP promptly. Do not stop or change the dose of any prescribed medicine without professional advice, as this can affect both your Parkinson's control and your erectile function.

Other medicines and conditions to consider with tadalafil

While tadalafil and entacapone can usually be taken together, it is vital to tell your prescriber about every medicine you use. Never take tadalafil with nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational 'poppers', as the combination can cause a life-threatening drop in blood pressure [4].

If you take alpha-blockers (such as tamsulosin, doxazosin, or alfuzosin) for prostate symptoms, your prescriber will ensure you are stable on the alpha-blocker and will usually start you on the lowest dose of tadalafil [4]. Potent CYP3A4 inhibitors—including some HIV medicines (ritonavir, cobicistat), antifungals (ketoconazole, itraconazole), and antibiotics (clarithromycin)—can raise tadalafil levels, requiring dose adjustments or avoidance [4].

Tadalafil is not suitable if you have had a recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (NAION) [4]. Erectile dysfunction can be an early warning sign of heart disease or diabetes, so if you are experiencing ED for the first time, it is important to see your GP for a full health check [1][2]. At Cured Pharmacy, our prescribers work within these safety guidelines to ensure your treatment is both effective and safe.

When to seek further advice

If tadalafil does not improve your erections after several attempts, or if you develop new symptoms such as chest pain, shortness of breath, or worsening dizziness, contact your GP or prescriber. Your doctor may need to adjust your dose, try a different ED treatment, or investigate other causes. Never increase your dose without professional guidance, and always report any side effects or concerns during follow-up consultations.

When to get urgent help

• An erection lasting more than 4 hours (priapism)—go to A&E immediately
• Sudden loss of vision or hearing—stop tadalafil and seek urgent medical help
• Chest pain during or after sex—call 999; do not take nitrates if you have used tadalafil
• Severe dizziness, fainting, or collapse—seek same-day medical attention
• Allergic reaction (swelling of face, lips, tongue, or difficulty breathing)—call 999

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

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