Vardenafil and St John's Wort: Can You Take Them Together?

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Vardenafil and St John's Wort: Understanding the Interaction

Published: 4 November 2026

Vardenafil and St John's wort can interact in a way that may reduce the effectiveness of your erectile dysfunction treatment. St John's wort is a herbal medicine often used for low mood, but it speeds up the breakdown of many prescription medicines in the body, including vardenafil. This page explains how the interaction works, what your prescriber will check, and practical steps to ensure your ED treatment remains safe and effective.

What is vardenafil and how does it work?

Vardenafil is a prescription medicine used to treat erectile dysfunction (ED) in men. It is the generic version of Levitra and belongs to a group of medicines called PDE5 inhibitors [5]. Vardenafil works by relaxing blood vessels in the penis, allowing more blood to flow in when you are sexually aroused. This helps you get and keep an erection suitable for sexual activity.

Vardenafil is available in 5 mg, 10 mg, and 20 mg tablets. You usually take it about 25 to 60 minutes before sexual activity, and it works only when you are sexually stimulated [5]. The medicine does not increase sexual desire and should be taken no more than once a day. Like all PDE5 inhibitors, vardenafil requires a prescription and a clinical assessment by a UK-registered prescriber to ensure it is safe and suitable for you.

What is St John's wort and why do people take it?

St John's wort (Hypericum perforatum) is a herbal medicine commonly used to relieve symptoms of mild low mood and anxiety. It is available over the counter in the UK from pharmacies, health food shops, and supermarkets. Many people choose St John's wort as a natural alternative to prescription antidepressants, although it is not suitable for moderate to severe depression.

Despite being a herbal product, St John's wort is a powerful medicine that can interact with many prescription drugs. It affects enzymes in the liver, particularly one called CYP3A4, which is responsible for breaking down a wide range of medicines [5]. When you take St John's wort, these enzymes work faster, meaning other medicines are removed from your body more quickly. This can make those medicines less effective, even if you are taking the correct dose.

How do vardenafil and St John's wort interact?

Vardenafil and St John's wort interact because St John's wort speeds up the activity of liver enzymes that break down vardenafil. Specifically, St John's wort is a CYP3A4 inducer, meaning it increases the rate at which the CYP3A4 enzyme metabolises vardenafil in your body [5]. When vardenafil is broken down more quickly, less of the active medicine remains in your bloodstream. This can reduce the effectiveness of vardenafil, meaning it may not work as well to help you achieve or maintain an erection.

The interaction does not cause a dangerous drop in blood pressure or other immediate safety concerns, unlike the serious interactions between vardenafil and nitrates or riociguat. However, the reduced effectiveness can be frustrating and may lead you to think the medicine is not working, when in fact the herbal supplement is interfering with it. This is why it is essential to tell your prescriber about all medicines, supplements, and herbal products you are taking, even those bought without a prescription.

What does CYP3A4 induction mean in plain English?

CYP3A4 is an enzyme in your liver that acts like a processing plant for medicines. When you take vardenafil, this enzyme breaks it down so your body can eventually remove it. St John's wort makes this enzyme work faster and more efficiently, so vardenafil is processed and cleared from your system more quickly than normal. The result is that the medicine does not stay in your body long enough to have its full effect, reducing the benefit you get from each dose.

What will my prescriber check before prescribing vardenafil?

Before prescribing vardenafil, your prescriber will ask about all the medicines, supplements, and herbal products you currently take. This includes over-the-counter items like St John's wort, vitamins, and other herbal remedies. They will check for any interactions that could make vardenafil unsafe or less effective. If you are taking St John's wort, your prescriber will discuss whether it is appropriate to continue it alongside vardenafil, or whether an alternative approach to managing your mood or your ED would be better.

Your prescriber will also review your medical history, including any heart conditions, blood pressure problems, recent stroke or heart attack, and other health issues that might affect whether vardenafil is suitable for you [2][5]. They will ask about other medicines that can interact seriously with vardenafil, such as nitrates (used for angina), nicorandil, riociguat, alpha-blockers, and potent CYP3A4 inhibitors like ritonavir or ketoconazole. The consultation ensures that vardenafil is prescribed safely and that you understand how to take it correctly.

Should I stop St John's wort before starting vardenafil?

If you are taking St John's wort and your prescriber recommends vardenafil for ED, they will usually advise you to stop the herbal medicine to allow vardenafil to work properly. However, you should never stop St John's wort suddenly without medical advice, especially if you have been taking it for low mood, as stopping abruptly can sometimes worsen symptoms. Your prescriber or GP can help you plan a safe way to reduce or stop St John's wort, and may suggest an alternative treatment for mood symptoms if needed. Always discuss any changes with a healthcare professional first.

Practical advice if you are taking both medicines

If you are currently taking St John's wort and considering treatment for erectile dysfunction, the most important step is to be open and honest during your consultation. Declare all herbal medicines and supplements, even if you think they are harmless or natural. Your prescriber can then give you tailored advice on whether to continue, stop, or switch treatments. In many cases, stopping St John's wort for a few weeks before starting vardenafil will allow the ED medicine to work as intended.

If you have already started vardenafil and it does not seem to be working, consider whether you have recently started taking St John's wort or any other new herbal product. Contact your prescriber or pharmacist to discuss the issue rather than increasing your dose on your own. They may recommend stopping the herbal medicine, trying a different PDE5 inhibitor, or adjusting your treatment plan. Remember that other factors can also affect how well vardenafil works, including heavy alcohol use, high-fat meals before taking the tablet, and underlying health conditions such as diabetes or high blood pressure [1][2].

Other medicines and lifestyle factors that affect vardenafil

St John's wort is not the only substance that can reduce the effectiveness of vardenafil. Other CYP3A4 inducers, such as the anticonvulsants carbamazepine and phenytoin, and the antibiotic rifampicin, can have a similar effect [5]. If you take any of these medicines, your prescriber will need to consider whether vardenafil is the best choice or whether a different ED treatment might be more suitable. On the other hand, potent CYP3A4 inhibitors like ritonavir, cobicistat, ketoconazole, and clarithromycin can raise vardenafil levels in the blood, increasing the risk of side effects. Vardenafil is usually avoided or contraindicated when you are taking these medicines.

Lifestyle factors also play a role in how well vardenafil works. Drinking large amounts of alcohol can make erectile dysfunction worse and add to the blood-pressure-lowering effect of vardenafil, increasing the risk of dizziness [5]. Grapefruit juice can raise the levels of vardenafil in your blood, so it is best to avoid it while taking this medicine. A healthy lifestyle, including regular exercise, a balanced diet, not smoking, and limiting alcohol, can improve the effectiveness of ED treatment and support your overall cardiovascular health [1][2].

When should I seek urgent medical help?

Seek urgent medical help if you experience an erection lasting more than four hours (priapism), sudden loss of vision or hearing, or chest pain during sexual activity while taking vardenafil [5]. These are rare but serious side effects that require immediate attention. If you feel dizzy, faint, or unwell after taking vardenafil, especially if you are also taking other blood-pressure medicines or have recently started or stopped St John's wort, contact your GP or NHS 111 for advice. Always read the patient information leaflet that comes with your medicine and follow the dosing instructions carefully.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 4 November 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 4 November 2026]
3. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 4 November 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.