Sildenafil and Voriconazole: Can They Be Taken Together?

Sildenafil and Voriconazole: Understanding the Interaction

Published: 16 October 2026

Sildenafil and voriconazole can interact because voriconazole is a potent CYP3A4 inhibitor that raises sildenafil levels in the blood, increasing the risk of side effects. This does not mean the combination is always unsafe, but it does require careful dose adjustment and monitoring by your prescriber. Understanding how these medicines interact helps you use sildenafil safely and effectively while taking voriconazole for a fungal infection.

What is sildenafil and voriconazole used for?

Sildenafil is a PDE5 inhibitor licensed to treat erectile dysfunction (ED) in men. It works by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused. Sildenafil is available as generic tablets (25mg, 50mg, and 100mg) and as the branded medicine Viagra. You take it about one hour before sexual activity, and it can help you get and maintain an erection suitable for sex [3].

Voriconazole is a prescription-only antifungal medicine used to treat serious fungal infections, including invasive aspergillosis and certain Candida infections. It belongs to the triazole class of antifungals and works by stopping fungi from making a protective outer layer, which kills the infection. Voriconazole is usually prescribed by specialists and is taken as tablets or given intravenously in hospital [12].

Both medicines are metabolised (broken down) in the liver by enzymes called cytochrome P450, particularly the CYP3A4 enzyme. Because voriconazole strongly inhibits this enzyme, it slows down how quickly your body clears sildenafil, leading to higher and longer-lasting levels of sildenafil in your bloodstream.

How do sildenafil and voriconazole interact?

Voriconazole is classified as a potent CYP3A4 inhibitor. When you take voriconazole, it blocks the CYP3A4 enzyme in your liver that normally breaks down sildenafil. As a result, sildenafil stays in your body for longer and reaches higher concentrations than it would on its own. This increases both the therapeutic effect and the risk of side effects such as headache, flushing, dizziness, visual disturbances, and a drop in blood pressure [3][12].

The interaction is pharmacokinetic, meaning it affects how your body processes sildenafil rather than how sildenafil works at its target. Clinical guidance states that when sildenafil is used alongside a potent CYP3A4 inhibitor like voriconazole, the starting dose of sildenafil should be reduced to minimise the risk of adverse effects. For sildenafil used for erectile dysfunction, a lower starting dose (typically 25mg) is recommended, and the maximum dose should not exceed 25mg within 48 hours [3][12].

Your prescriber will review your current medicines during the online consultation to check for this interaction. They will adjust your sildenafil dose if you are taking voriconazole or any other potent CYP3A4 inhibitor. It is essential to declare all your current medicines, including those prescribed by specialists, so that the prescriber can make safe, individualised recommendations.

Why dose adjustment matters

Taking the usual dose of sildenafil while on voriconazole can lead to sildenafil levels that are several times higher than intended. This raises the likelihood of side effects, some of which—such as a significant drop in blood pressure or prolonged erection (priapism)—can be serious. Reducing the sildenafil dose keeps the medicine effective while lowering the risk of harm. Your prescriber will tailor the dose to your individual circumstances, taking into account your age, other health conditions, and all the medicines you are taking.

What your prescriber checks before approving sildenafil and voriconazole together

During your online consultation at Cured Pharmacy, the UK-registered prescriber will ask about all your current medicines, including voriconazole and any other antifungals, antibiotics, or antivirals. They will check for other CYP3A4 inhibitors and any medicines that are absolutely contraindicated with sildenafil, such as nitrates (GTN spray, isosorbide mononitrate), nicorandil, riociguat, or recreational drugs known as poppers [3].

The prescriber will also review your cardiovascular health, blood pressure, and any history of liver or kidney problems, as these can further affect how your body handles sildenafil. If you are taking voriconazole, they will typically recommend starting with sildenafil 25mg and advise you not to take more than one dose in 48 hours. They may also discuss alternative PDE5 inhibitors if appropriate, though many require similar dose adjustments or are contraindicated with potent CYP3A4 inhibitors [3][5][6].

You should never adjust your sildenafil dose yourself or take sildenafil from another source while on voriconazole without first consulting a prescriber. The interaction is well-documented, and safe use depends on individualised dosing and monitoring.

Practical advice for taking sildenafil with voriconazole

If your prescriber approves sildenafil while you are on voriconazole, start with the lowest dose (usually 25mg) and take it about one hour before planned sexual activity. Do not take more than one dose in 48 hours, as the prolonged presence of both medicines in your system increases the risk of side effects. Sexual stimulation is still required for sildenafil to work; it does not cause an automatic erection [3].

Be alert for common side effects such as headache, facial flushing, indigestion, nasal congestion, and dizziness. These are more likely when sildenafil levels are elevated. Avoid drinking grapefruit juice, as it can further raise sildenafil levels, and limit alcohol, which can worsen erectile dysfunction and add to the blood-pressure-lowering effect of sildenafil [3][12].

If you experience visual disturbances (such as a blue tinge to vision or increased sensitivity to light), stop taking sildenafil and contact your GP or pharmacist. Seek urgent medical help if you have an erection lasting more than four hours, sudden loss of vision or hearing, or chest pain during sex. Always keep your GP and specialist informed about all the medicines you are taking, including those obtained online.

When to seek advice

Contact your prescriber or pharmacist if you start or stop voriconazole or any other antifungal, antibiotic, or antiviral medicine while using sildenafil. Changes to your medication regimen can alter the interaction and may require a new dose adjustment. Do not stop taking voriconazole without your specialist's advice, as this is treating a serious infection. Your healthcare team can work together to ensure both your infection and erectile dysfunction are managed safely.

Other antifungal medicines and sildenafil interactions

Voriconazole is not the only antifungal that can interact with sildenafil. Other azole antifungals, such as ketoconazole and itraconazole, are also potent CYP3A4 inhibitors and require similar dose reductions of sildenafil [3][12]. Fluconazole is a moderate CYP3A4 inhibitor and may also raise sildenafil levels, though usually to a lesser extent; your prescriber will assess the need for dose adjustment based on the fluconazole dose and duration.

Posaconazole, another triazole antifungal, can also inhibit CYP3A4, and caution is advised when used with sildenafil. In contrast, some antifungals such as terbinafine (commonly used for nail infections) do not significantly affect CYP3A4 and are not expected to interact with sildenafil in the same way. However, you should always declare every medicine you are taking during your consultation, as individual factors and combination effects can vary [12].

If you are prescribed an antifungal for a short course (for example, fluconazole for thrush), inform your prescriber so they can advise whether to pause sildenafil temporarily or adjust the dose. For long-term antifungal therapy, ongoing monitoring and dose adjustment ensure you can continue ED treatment safely.

Alternatives to sildenafil when taking voriconazole

If dose-adjusted sildenafil is not suitable or effective for you while taking voriconazole, your prescriber may discuss alternative treatments for erectile dysfunction. Tadalafil (Cialis) is another PDE5 inhibitor that also interacts with CYP3A4 inhibitors, but the dose adjustment is different: the maximum recommended dose is reduced (for example, 10mg every 72 hours), and daily tadalafil is not recommended with potent inhibitors [4][12].

Vardenafil and avanafil are generally contraindicated or not recommended with potent CYP3A4 inhibitors such as voriconazole, as the interaction can lead to significantly elevated drug levels and a higher risk of serious side effects [5][6][12]. Non-oral treatments, such as Eroxon gel (a topical medical device that does not interact with voriconazole) or alprostadil (Vitaros cream or Caverject injection), may be considered if oral PDE5 inhibitors are unsuitable [7].

Your prescriber will take into account your preferences, the severity of your ED, your overall health, and the duration of your voriconazole treatment when recommending the most appropriate option. In some cases, it may be safest to wait until your antifungal course is complete before starting or resuming a PDE5 inhibitor, particularly if the infection is being treated short-term.

Discussing your options

Erectile dysfunction can have a significant impact on quality of life and relationships, so it is important to find a treatment that works for you safely. Be open with your prescriber about your concerns, how well previous ED treatments have worked, and any side effects you have experienced. They can tailor a plan that balances effective ED management with the safe use of voriconazole and any other medicines you need.

Scientific References

1. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 16 October 2026]
2. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 16 October 2026]
3. Joint Formulary Committee. (n.d.). Vardenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/vardenafil/ [accessed 16 October 2026]
4. Joint Formulary Committee. (n.d.). Avanafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/avanafil/ [accessed 16 October 2026]
5. Joint Formulary Committee. (n.d.). Alprostadil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/alprostadil/ [accessed 16 October 2026]
6. Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 16 October 2026]
7. NHS. (n.d.). Erectile dysfunction (impotence). https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ Accessed 16 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.