Tadalafil and Lacosamide: Can They Be Taken Together?

Tadalafil and Lacosamide: Understanding the Interaction

Published: 22 October 2026

If you're prescribed lacosamide for epilepsy and considering tadalafil for erectile dysfunction (ED), you may wonder whether tadalafil and lacosamide can be taken together safely. The good news is that no major direct interaction between these two medicines is commonly reported in clinical practice. However, both medications can affect your cardiovascular system in different ways, so your prescriber will carefully review your full medical history and current medicines during your consultation to ensure the combination is appropriate for you.

What is tadalafil and lacosamide used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed to treat erectile dysfunction in men [4]. It works by relaxing blood vessels in the penis, allowing increased blood flow when you're sexually aroused. Tadalafil is available as generic Cialis in two forms: on-demand tablets (10mg or 20mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) and daily low-dose tablets (2.5mg or 5mg taken once a day) [4]. It requires sexual stimulation to work and does not increase libido on its own.

Lacosamide is an anti-epileptic drug (also called an anticonvulsant) used to treat partial-onset seizures in adults and children with epilepsy. It works by stabilising overactive electrical activity in the brain. Lacosamide can affect the heart's electrical conduction system, which is why your doctor monitors your heart rhythm, especially when starting treatment or increasing the dose. It's important never to stop lacosamide suddenly without medical advice, as this can trigger seizures.

Is there an interaction between tadalafil and lacosamide?

There is no well-documented direct pharmacological interaction between tadalafil and lacosamide. They work through different mechanisms in the body: tadalafil primarily affects blood vessels, while lacosamide acts on nerve cells in the brain. Neither medicine is known to significantly alter the metabolism or blood levels of the other, so they are not expected to interfere with each other's effectiveness.

However, both medicines can have cardiovascular effects that your prescriber must consider. Tadalafil can cause a modest drop in blood pressure, which is usually well tolerated but may cause dizziness in some men [4]. Lacosamide can affect the heart's electrical conduction (the PR interval on an ECG) and has been associated with dizziness and, rarely, heart rhythm disturbances. When taken together, there is a theoretical possibility that these effects could add up, particularly if you have existing heart problems.

This is why every prescription for tadalafil at Cured Pharmacy requires a clinical consultation reviewed by a UK-registered prescriber. During this assessment, you'll be asked about all your current medicines, including lacosamide, your seizure control, any heart conditions, and whether you experience dizziness or fainting. The prescriber will determine whether tadalafil is safe and appropriate for you, and may recommend starting on a lower dose or arranging additional monitoring if needed.

How the prescriber assesses your suitability

Your prescriber will review your epilepsy history, how well controlled your seizures are, and whether you have any cardiovascular conditions such as high or low blood pressure, heart rhythm problems, or a history of heart attack or stroke. They will also check for any other medicines you take that might interact with tadalafil, such as nitrates (which are an absolute contraindication), alpha-blockers, or other blood-pressure-lowering drugs. If you're stable on lacosamide with good seizure control and no significant heart issues, tadalafil is usually considered safe, but the decision is always individualised.

What your prescriber checks before approving tadalafil and lacosamide together

During your online consultation, the prescriber will ask detailed questions to ensure tadalafil is safe for you. Key areas include your current dose of lacosamide and how long you've been taking it, whether you've had any recent changes to your epilepsy treatment, and whether you experience side effects such as dizziness, blurred vision, or heart palpitations. They will also ask about your blood pressure, any history of fainting or blackouts, and whether you have angina, heart failure, or other cardiovascular conditions [2].

The prescriber will check for absolute contraindications to tadalafil, such as use of nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs called 'poppers' (amyl or alkyl nitrites). If you take any of these, you must not use tadalafil, as the combination can cause a dangerous drop in blood pressure [4]. They will also review any other prescription or over-the-counter medicines, herbal supplements (such as St John's wort), and your alcohol intake.

If you have a history of heart rhythm problems or your lacosamide dose has recently been increased, the prescriber may recommend you discuss tadalafil with your neurologist or cardiologist first, or they may suggest starting on the lowest effective dose of tadalafil (such as 10mg on-demand) and monitoring how you respond. This careful, individualised approach ensures your safety while helping you access effective ED treatment.

Practical advice for taking tadalafil and lacosamide safely

If your prescriber approves tadalafil, continue taking lacosamide exactly as prescribed by your neurologist or GP. Never stop or reduce lacosamide without medical advice, as sudden withdrawal can trigger seizures. Take tadalafil as directed: on-demand tablets (10mg or 20mg) should be taken at least 30 minutes before sexual activity, while daily tablets (2.5mg or 5mg) are taken once a day at the same time [4]. Do not take more than one dose of on-demand tadalafil in 24 hours.

Be aware of how both medicines might make you feel, especially when you first start tadalafil. Common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. Lacosamide commonly causes dizziness, headache, nausea, and double vision, particularly when starting or increasing the dose. If you feel dizzy or lightheaded, avoid driving or operating machinery, and get up slowly from sitting or lying down to reduce the risk of falls.

Limit alcohol while taking tadalafil, as heavy drinking can worsen erectile dysfunction and add to the blood-pressure-lowering effect, increasing dizziness [4]. Grapefruit juice can raise tadalafil levels in your blood, so it's best to avoid it. If you develop any new or worsening symptoms after starting tadalafil—such as severe dizziness, fainting, chest pain, or changes in your seizure pattern—contact your GP or specialist promptly. Always inform any healthcare professional you see (including your dentist or pharmacist) that you take both lacosamide and tadalafil.

When to seek urgent medical help

Seek immediate medical attention (call 999 or go to A&E) if you experience an erection lasting more than four hours (priapism), sudden loss of vision in one or both eyes, sudden decrease or loss of hearing, or chest pain during sexual activity. If you have a seizure that is different from your usual pattern, lasts longer than normal, or if you have multiple seizures in quick succession, this also requires urgent assessment. These situations are rare but need prompt treatment to prevent serious complications.

Other erectile dysfunction treatments and lacosamide

If tadalafil is not suitable for you, or if you'd like to explore alternatives, other PDE5 inhibitors are available and work in a similar way. Sildenafil (generic Viagra) is taken about one hour before sex, with effects lasting around four to six hours [3]. Vardenafil (generic Levitra) works in about 25 to 60 minutes, and avanafil (Spedra) can work in as little as 15 to 30 minutes [5][6]. All PDE5 inhibitors have similar interactions and precautions, so the same careful assessment applies if you take lacosamide.

The choice between different PDE5 inhibitors often comes down to how quickly you want the medicine to work, how long you want the effect to last, and personal preference. Tadalafil's longer duration (up to 36 hours) offers more spontaneity, while sildenafil and the faster-acting options may suit men who prefer to plan ahead. Your prescriber can discuss which option best fits your lifestyle and medical history.

Non-tablet options include Eroxon, a topical gel that works locally and does not enter the bloodstream significantly, so it has minimal interaction risk. Prescription treatments such as Vitaros (alprostadil cream applied to the tip of the penis) or Caverject (alprostadil injection) work differently from PDE5 inhibitors and may be considered if tablets are unsuitable [7]. Your GP or a specialist can advise on these alternatives if needed.

Why treating erectile dysfunction matters for your overall health

Erectile dysfunction is common, affecting about half of men aged 40 to 70 to some degree [10]. It can have many causes, including reduced blood flow, nerve damage, hormonal imbalances, psychological factors such as stress or anxiety, and side effects of other medicines. For men with epilepsy, ED may be more common due to the condition itself, the effects of anti-epileptic drugs, or associated psychological stress [1].

It's important to see your GP if you're experiencing new or worsening ED, as it can be an early warning sign of cardiovascular disease or diabetes [2]. Your GP can check your blood pressure, cholesterol, blood sugar, and hormone levels, and review whether any of your current medicines (including lacosamide or other anti-epileptics) might be contributing. Addressing underlying health issues not only improves your sexual health but also reduces your risk of heart attack and stroke.

Once any underlying causes have been identified and managed, ED treatments such as tadalafil can be very effective. Clinical trials show that PDE5 inhibitors help the majority of men achieve erections sufficient for sexual activity [9]. At Cured Pharmacy, our online consultation is reviewed by UK-registered prescribers who understand the complexities of treating ED in men with other health conditions, including epilepsy. Treatment is discreet, convenient, and tailored to your individual needs, with ongoing support from our pharmacy team.

Living well with epilepsy and ED

Managing both epilepsy and erectile dysfunction can feel challenging, but effective treatments are available for both conditions. Good seizure control, a healthy lifestyle (regular exercise, balanced diet, not smoking, moderate alcohol), and open communication with your healthcare team and partner all contribute to better outcomes. Many men find that successfully treating ED improves their confidence, relationships, and overall quality of life. You don't have to manage these issues alone—support is available, and treatment can make a real difference.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 22 October 2026]
2. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 22 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 22 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 22 October 2026]
5. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 22 October 2026]
6. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 22 October 2026]
7. Joint Formulary Committee. (n.d.). Alprostadil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/alprostadil/ [accessed 22 October 2026]
8. Goldstein, I., Lue, T. F., Padma-Nathan, H., Rosen, R. C., Steers, W. D., & Wicker, P. A. (1998). Oral sildenafil in the treatment of erectile dysfunction. New England Journal of Medicine, 338(20), 1397–1404. https://pubmed.ncbi.nlm.nih.gov/9580646/ [accessed 22 October 2026]
9. Feldman, H. A., Goldstein, I., Hatzichristou, D. G., Krane, R. J., & McKinlay, J. B. (1994). Impotence and its medical and psychosocial correlates: Results of the Massachusetts Male Aging Study. Journal of Urology, 151(1), 54–61. https://pubmed.ncbi.nlm.nih.gov/8254833/ [accessed 22 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.

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