Tadalafil and Donepezil: Can They Be Taken Together?

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Tadalafil and Donepezil: Understanding the Interaction

Published: 20 October 2026

Many men taking donepezil for Alzheimer's disease or dementia wonder whether tadalafil and donepezil can be taken together safely. The good news is that no major interaction is commonly reported between these two medicines, and they are often prescribed together. However, both medicines can affect your heart rate and blood pressure in different ways, so your prescriber will need to review your full medical history and current health before approving tadalafil.

What is tadalafil and donepezil used for?

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 more blood to flow in when you are sexually aroused [3][4]. Tadalafil is available as an on-demand treatment (usually 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). It requires sexual stimulation to work and does not increase sexual desire on its own.

Donepezil is a medicine used to treat symptoms of Alzheimer's disease and other forms of dementia. It belongs to a class of drugs called acetylcholinesterase inhibitors, which work by increasing levels of a chemical messenger (acetylcholine) in the brain that is important for memory and thinking [12]. Donepezil is usually taken once a day, often at bedtime, and is available in 5 mg and 10 mg strengths. It does not cure dementia but may help slow the worsening of symptoms for a period of time.

Both medicines are prescription-only in the UK. Tadalafil is supplied by Cured Pharmacy after an online consultation reviewed by a UK-registered prescriber, who will check your current medicines, including donepezil, to ensure the combination is suitable for you.

Can you take tadalafil and donepezil together?

Yes, tadalafil and donepezil can usually be taken together. No major interaction between these two medicines is commonly reported in the British National Formulary or other UK prescribing resources [3][4][12]. Many men with dementia who are taking donepezil also experience erectile dysfunction and are safely prescribed tadalafil or other PDE5 inhibitors alongside their dementia treatment.

However, both medicines can have effects on your cardiovascular system. Tadalafil can lower blood pressure slightly, which is usually well tolerated but may cause dizziness in some people, especially when standing up quickly [4]. Donepezil can sometimes slow the heart rate or cause changes in heart rhythm, particularly in people with existing heart conditions [12]. Because of these individual effects, your prescriber will need to review your overall heart health, blood pressure, and any other medicines you take before approving tadalafil.

It is essential that you declare donepezil (and all other medicines, including over-the-counter products and supplements) during your online consultation. The prescriber will assess whether the combination is safe for you personally, taking into account your age, other health conditions, and the doses of both medicines. Never start, stop, or change the dose of either medicine without professional advice.

How the interaction works (in plain English)

Tadalafil and donepezil work on completely different systems in the body, which is why they do not directly interfere with each other. Tadalafil acts on blood vessels, while donepezil acts on brain chemistry. The main consideration is that both can have indirect effects on the heart and circulation. Tadalafil relaxes blood vessels throughout the body, which can lower blood pressure, and donepezil can affect the electrical signals that control your heartbeat. In most people, these effects are mild and do not cause problems when the medicines are used together, but your prescriber will check that your heart and blood pressure are healthy enough for sexual activity and for the combination of treatments.

What your prescriber checks before approving tadalafil and donepezil together

During your online consultation at Cured Pharmacy, the prescriber will ask detailed questions to ensure tadalafil is safe for you while you are taking donepezil. They will check your current blood pressure, as tadalafil can lower it further. If you have low blood pressure (hypotension) or experience frequent dizziness, the prescriber may advise against tadalafil or recommend a lower starting dose [4].

The prescriber will also ask about your heart health. Tadalafil is not suitable if sexual activity is inadvisable for you—for example, if you have had a recent heart attack or stroke, unstable angina, or severe heart failure [1][4]. Because donepezil can sometimes affect heart rhythm, the prescriber will want to know if you have any heart conditions, particularly irregular heartbeats (arrhythmias) or a slow pulse. If you do, they may consult with your GP or cardiologist before prescribing.

You will be asked to list all your current medicines. Tadalafil must never be taken with nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called 'poppers', as the combination can cause a dangerous drop in blood pressure [3][4]. If you take alpha-blockers for prostate symptoms (such as tamsulosin or doxazosin), the prescriber will check that you are stable on that treatment and may start you on the lowest dose of tadalafil. The prescriber will also review any other medicines that might interact, including some antibiotics and antifungals.

Practical advice for taking tadalafil and donepezil safely

If your prescriber approves tadalafil while you are taking donepezil, follow these practical tips to use both medicines safely. Take each medicine exactly as prescribed. Donepezil is usually taken once daily, often in the evening, and should be swallowed whole with water [12]. Tadalafil on-demand tablets (10 mg or 20 mg) are taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours; daily tadalafil (2.5 mg or 5 mg) is taken at the same time each day, regardless of when you plan to have sex [4].

Be aware of how you feel when you stand up, especially in the first few days of taking tadalafil. Both medicines can contribute to dizziness or light-headedness, particularly if you get up quickly from sitting or lying down. If you feel dizzy, sit or lie down until it passes, and move slowly when changing position. Avoid drinking large amounts of alcohol, as this can make dizziness worse and also reduce the effectiveness of tadalafil [3][4].

Do not take tadalafil more often than prescribed (usually no more than once a day for on-demand use). If you miss a dose of donepezil, take it as soon as you remember unless it is nearly time for your next dose; do not double up. Keep both medicines in their original packaging, out of reach of children, and check the expiry dates. If you experience any new or worsening symptoms—such as chest pain, severe dizziness, fainting, or an erection lasting more than four hours—seek medical help immediately.

Monitoring and follow-up

Your GP or specialist will usually monitor your response to donepezil regularly, including checking your heart rate and overall health. It is a good idea to mention to your GP that you are also taking tadalafil, so they have a complete picture of your medicines. If you notice any changes in your heart rhythm, new dizziness, or any other side effects after starting tadalafil, contact your GP or the prescribing pharmacist. Regular blood pressure checks can also be helpful, especially in the first few weeks of using tadalafil, to ensure it is not lowering your blood pressure too much.

Other medicines that may interact with tadalafil and donepezil

While tadalafil and donepezil do not interact significantly with each other, both medicines can interact with other treatments you may be taking. For tadalafil, the most important interactions to avoid are with nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, and recreational nitrites ('poppers'). Do not take tadalafil with any of these, as the combination can cause a dangerous fall in blood pressure [3][4].

Alpha-blockers, used for prostate enlargement or high blood pressure (such as tamsulosin, doxazosin, alfuzosin), can also lower blood pressure when combined with tadalafil. If you take an alpha-blocker, you must be stable on it before starting tadalafil, and your prescriber will usually recommend the lowest dose of tadalafil to start [4]. Some medicines that affect liver enzymes—such as ritonavir, cobicistat (found in some HIV treatments and in Paxlovid), ketoconazole, itraconazole, and clarithromycin—can raise tadalafil levels in your blood, requiring a lower dose or avoidance [4][12].

For donepezil, interactions can occur with medicines that also slow the heart (such as beta-blockers like bisoprolol or atenolol, or certain calcium-channel blockers like diltiazem or verapamil) or with other medicines that affect acetylcholine [12]. Always tell your prescriber and GP about every medicine you take, including over-the-counter products, herbal remedies (such as St John's wort), and supplements. Never stop or change a prescribed medicine without professional advice.

When to seek help and what to watch for with tadalafil and donepezil

Most men taking tadalafil and donepezil together do not experience serious problems, but it is important to know the warning signs that need urgent attention. If you develop chest pain or discomfort during or after sexual activity, stop what you are doing and seek medical help immediately. Do not take a nitrate medicine (such as GTN spray) if you have used tadalafil in the past 48 hours, as this combination is dangerous [4]. Call 999 or go to A&E if you have severe chest pain.

An erection that lasts longer than four hours (priapism) is a medical emergency and requires immediate treatment to prevent permanent damage to the penis [3][4]. Sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness), are rare but serious side effects of PDE5 inhibitors and require urgent medical attention [3][4]. If you experience severe dizziness, fainting, or a very slow or irregular heartbeat, contact your GP or call 111 for advice.

Common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and a stuffy or runny nose; these are usually mild and temporary [4]. Donepezil can cause nausea, diarrhoea, muscle cramps, tiredness, and sleep disturbances [12]. If any side effect becomes troublesome or does not go away, speak to your pharmacist or GP. Always report any new symptoms after starting tadalafil, especially if you are also taking donepezil or other medicines for dementia.

Alternatives if tadalafil is not suitable

If tadalafil is not suitable for you while taking donepezil—for example, because of other health conditions or medicine interactions—there are alternative treatments for erectile dysfunction. Other PDE5 inhibitors, such as sildenafil (Viagra), vardenafil (Levitra), or avanafil (Spedra), work in a similar way to tadalafil and have similar interactions and precautions [3][5][6]. Your prescriber can discuss which option may be best for you. Non-tablet treatments include Eroxon gel (a medical device available without prescription), Vitaros cream (alprostadil, applied inside the urethra), or Caverject injections (alprostadil, injected into the penis) [7]. Vacuum erection devices and penile implants are also options for some men. Your GP or a specialist can provide advice tailored to your situation.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 20 October 2026]
2. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 20 October 2026]
3. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 20 October 2026]
4. Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 20 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.