Tadalafil and Zonisamide: Can You Take Them Together?

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Key takeaways

• No major direct interaction between tadalafil and zonisamide is commonly reported in clinical practice.
• Both medicines can cause dizziness, so be cautious when standing up quickly or drinking alcohol.
• Your prescriber will review all your medicines during your consultation to ensure tadalafil is safe for you.
• Never take tadalafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor.
• Seek urgent help if you have chest pain, an erection lasting over four hours, or sudden vision or hearing loss.

What is tadalafil and how does it work?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused [3][4].

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

Common brand names include Cialis, and generic versions are widely available. At Cured Pharmacy, tadalafil is supplied after an online consultation reviewed by a UK-registered prescriber, who will check your medical history and current medicines to ensure it is safe and appropriate for you.

What is zonisamide and why is it prescribed?

Zonisamide is an antiepileptic (anticonvulsant) medicine primarily used to treat epilepsy, either alone or in combination with other seizure medicines. It works by stabilising electrical activity in the brain to help prevent seizures. In some cases, zonisamide is also prescribed off-label for migraine prevention or as an adjunct in certain movement disorders.

Zonisamide is usually taken once or twice daily, and the dose is carefully adjusted by your doctor based on your response and any side effects. Common side effects include drowsiness, dizziness, loss of appetite, and difficulty concentrating, especially when you first start treatment or when the dose is increased.

Because zonisamide affects the nervous system, it is important to tell your prescriber about all medicines you take, including over-the-counter products and supplements, to avoid unexpected interactions or side effects.

At a glance

Do tadalafil and zonisamide interact with each other?

There is no well-documented direct pharmacological interaction between tadalafil and zonisamide. They work through different mechanisms in different parts of the body: tadalafil acts on blood vessels in the penis, while zonisamide affects electrical activity in the brain. Neither medicine is known to significantly alter the metabolism or effectiveness of the other.

However, both medicines can cause dizziness or light-headedness as side effects. Tadalafil can lower blood pressure slightly, and zonisamide may cause dizziness, particularly when you first start taking it or when standing up quickly. Taking them together may, in theory, add to these effects, so it is sensible to be cautious, especially when you first combine them.

Your prescriber will review your full medical history, including your epilepsy control, blood pressure, and any other medicines you take, to ensure tadalafil is safe for you. If you experience unusual dizziness, fainting, or any new symptoms after starting tadalafil, contact your GP or pharmacist for advice.

What your prescriber will check

During your online consultation at Cured Pharmacy, the prescriber will ask about your current medicines, including zonisamide, to check for any potential interactions or contraindications. They will also review your cardiovascular health, blood pressure, and whether you take any medicines that are known to interact dangerously with tadalafil, such as nitrates, nicorandil, or riociguat [4].

If you are stable on zonisamide and have no other contraindications, tadalafil is usually considered safe to prescribe. The prescriber may recommend starting on a lower dose of tadalafil to minimise the risk of side effects, and they will provide clear instructions on how and when to take it.

Are there any medicines you should never take with tadalafil?

Yes. Do not take tadalafil if you are using nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites). Combining tadalafil with any of these can cause a dangerous, potentially life-threatening drop in blood pressure [3][4].

You must also never take tadalafil alongside another PDE5 inhibitor, such as sildenafil (Viagra), vardenafil (Levitra), or avanafil (Spedra), as this increases the risk of serious side effects. Always tell your prescriber about every medicine you take, including over-the-counter products, herbal remedies, and recreational substances.

Other medicines that require careful prescriber review include alpha-blockers (such as doxazosin or tamsulosin, used for prostate problems or high blood pressure), potent CYP3A4 inhibitors (such as ritonavir, ketoconazole, or clarithromycin), and other blood-pressure-lowering medicines. Your prescriber will adjust your tadalafil dose or advise against its use if necessary [4].

Practical advice for taking tadalafil and zonisamide together

If your prescriber approves tadalafil while you are taking zonisamide, take each medicine exactly as directed. Do not stop, start, or change the dose of zonisamide without your doctor's advice, as this could affect your seizure control. Similarly, follow the instructions for tadalafil carefully—on-demand tablets should be taken at least 30 minutes before sexual activity, and daily tablets should be taken at the same time each day [4].

Be mindful of dizziness, especially when standing up quickly or after drinking alcohol. Heavy alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of tadalafil, so it is best to drink in moderation or avoid alcohol when planning to use tadalafil [1][4].

If you experience any new or worsening symptoms—such as severe dizziness, fainting, chest pain during sex, an erection lasting more than four hours, or sudden loss of vision or hearing—seek urgent medical help. Keep your GP and pharmacist informed of all the medicines you take, and do not hesitate to ask questions during your consultation.

Lifestyle tips to support erectile function

Erectile dysfunction can be an early warning sign of cardiovascular disease or diabetes, so it is important to see your GP for a full health check if you have new or worsening ED [1][2]. Managing underlying conditions, maintaining a healthy weight, exercising regularly, stopping smoking, and reducing stress can all improve erectile function and overall health.

Tadalafil works best when combined with a healthy lifestyle. It requires sexual stimulation to be effective, so open communication with your partner and addressing any psychological factors (such as anxiety or relationship stress) can also make a significant difference [2].

How to get tadalafil safely from Cured Pharmacy

At Cured Pharmacy, a GPhC-registered online pharmacy (GPhC 9012511), you can request tadalafil through a straightforward online consultation. You will be asked about your medical history, current medicines (including zonisamide), and any other health conditions. A UK-registered prescriber will review your answers to ensure tadalafil is safe and suitable for you.

If approved, your prescription will be dispensed by our pharmacy team and delivered discreetly to your door. We offer a range of tadalafil options, including generic and branded versions, at transparent prices. For example, generic tadalafil starts at £7.95 (or £6.36 for your first order with code Ednew), and branded Cialis is available at £12.00 (or £9.60 with code Ednew).

Our pharmacists are available to answer any questions about your treatment, including how tadalafil and zonisamide may interact, what side effects to watch for, and how to use your medicine safely. We are here to support your health and wellbeing with professional, confidential care.

Why choose Cured Pharmacy?

Cured Pharmacy combines the convenience of online ordering with the expertise of experienced UK pharmacists and prescribers. Every consultation is reviewed individually, and we never supply prescription medicines without a proper clinical assessment. Our service is designed to be discreet, supportive, and genuinely helpful, with clear information and transparent pricing.

We stock a full range of licensed ED treatments, including sildenafil, tadalafil, vardenafil, and avanafil, so you and your prescriber can choose the option that best suits your needs and lifestyle. All our medicines are sourced from licensed UK wholesalers and meet the highest quality standards.

When to get urgent help

• An erection lasting more than four hours (priapism)—go to A&E immediately
• Sudden loss of vision or hearing—stop tadalafil and seek urgent medical advice
• Chest pain during or after sex—stop sexual activity, sit down, and call 999 if pain does not resolve quickly
• Severe dizziness, fainting, or collapse—seek same-day medical advice or call 999 if symptoms are severe
• Allergic reaction (rash, swelling of face or throat, difficulty breathing)—call 999 immediately

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