Tadalafil and Posaconazole: Can They Be Taken Together?

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Key takeaways

• Posaconazole raises tadalafil levels by blocking the enzyme that breaks it down, increasing side-effect risk.
• Your prescriber will reduce the maximum tadalafil dose to 10 mg per 72 hours if you take posaconazole.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers—this can cause dangerous low blood pressure.
• Report severe headache, dizziness, chest pain, or erection lasting over 4 hours immediately.
• Always tell your prescriber about every medicine you take to avoid harmful interactions.

What is tadalafil and posaconazole used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED) and the urinary symptoms of an enlarged prostate [4]. It works by relaxing blood vessels in the penis, helping you get and keep an erection when sexually aroused. Tadalafil is available on-demand (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 (2.5 mg or 5 mg) for continuous readiness [4]. It requires sexual stimulation to work and does not increase sexual desire on its own.

Posaconazole is a prescription antifungal medicine used to prevent and treat serious fungal infections, particularly in people with weakened immune systems—for example, those undergoing chemotherapy or stem-cell transplants [12]. It belongs to the azole class of antifungals and works by stopping fungi from growing. Posaconazole is a potent inhibitor of an enzyme called CYP3A4, which is responsible for breaking down many medicines in the liver, including tadalafil [12]. This is why the two medicines can interact when taken together.

How do tadalafil and posaconazole interact?

The interaction between tadalafil and posaconazole occurs because posaconazole strongly inhibits CYP3A4, the main enzyme that metabolises (breaks down) tadalafil in your liver [4][12]. When this enzyme is blocked, tadalafil stays in your body for longer and reaches higher concentrations in your blood than it normally would. Studies show that potent CYP3A4 inhibitors can more than double the levels of tadalafil, which increases the likelihood and severity of side effects [4].

Common side effects of tadalafil—such as headache, flushing, indigestion, back pain, muscle aches, and nasal congestion—may become more pronounced [4]. More importantly, higher tadalafil levels can lead to a greater drop in blood pressure, causing dizziness, fainting, or (rarely) priapism, a painful erection lasting more than four hours that requires emergency treatment [4]. Because of this interaction, your prescriber must reduce the maximum dose of tadalafil if you are taking posaconazole or another potent CYP3A4 inhibitor.

Why CYP3A4 matters

CYP3A4 is one of the most important enzymes in your liver for processing medicines. Many commonly prescribed drugs—including some antibiotics (clarithromycin), antivirals (ritonavir, cobicistat, Paxlovid), and other antifungals (ketoconazole, itraconazole)—also inhibit this enzyme [3][4][5][6]. If you take any of these alongside tadalafil, the same dose-adjustment rules apply. Always tell your prescriber about every medicine you take, including over-the-counter products and herbal supplements, so they can check for interactions and adjust doses safely.

At a glance

What does your prescriber check before prescribing tadalafil and posaconazole together?

Your prescriber will review your full medication list to confirm you are taking posaconazole and check for any other interacting medicines [2][4]. They will assess your cardiovascular health, including blood pressure, because tadalafil can lower blood pressure and this effect is amplified when levels are raised by posaconazole [4]. If you also take medicines for high blood pressure or an alpha-blocker for prostate symptoms (such as tamsulosin or doxazosin), the prescriber must ensure you are stable on those treatments and consider starting tadalafil at the lowest possible dose [4].

The prescriber will also confirm that you do not take any medicines that are absolutely contraindicated with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate), nicorandil, riociguat, or recreational drugs known as poppers (amyl or alkyl nitrites) [4]. Combining tadalafil with any of these can cause a dangerous, potentially life-threatening drop in blood pressure—do not take them together under any circumstances. Your prescriber will also ask about any history of heart problems, stroke, liver or kidney disease, eye conditions (especially a previous episode of sudden vision loss called NAION), and whether sexual activity is safe for you [2][4].

Dose adjustments for tadalafil when taking posaconazole

Because posaconazole raises tadalafil levels significantly, the British National Formulary and the medicine's Summary of Product Characteristics recommend a reduced maximum dose of tadalafil [4][12]. For on-demand use, the maximum single dose is typically reduced to 10 mg in any 72-hour period (rather than the usual 20 mg in 24 hours) when you are taking a potent CYP3A4 inhibitor such as posaconazole [4]. Your prescriber may start you on an even lower dose—such as 5 mg—to see how you respond and minimise side effects.

If you are considering daily tadalafil (2.5 mg or 5 mg once a day), your prescriber will carefully weigh the benefits and risks, as continuous exposure to raised tadalafil levels may not be advisable while you are on posaconazole [4]. In some cases, they may recommend pausing daily tadalafil during your course of posaconazole, or switching to on-demand dosing at a reduced dose. Never adjust your tadalafil dose yourself—always follow your prescriber's instructions and report any side effects promptly.

What if I'm already taking tadalafil?

If you are already using tadalafil and your doctor prescribes posaconazole (or vice versa), inform both prescribers immediately so they can review your treatment plan [4][12]. You may need to reduce your tadalafil dose or take a treatment break while on posaconazole. Do not stop either medicine without medical advice, especially posaconazole, as stopping an antifungal early can allow the infection to return or become resistant. Your pharmacist can also check for interactions when you collect your prescriptions and will contact your prescriber if a dose adjustment is needed.

Practical advice for taking tadalafil and posaconazole safely

Always take both medicines exactly as prescribed and do not exceed the recommended dose of tadalafil, even if you feel it is not working as well as before [4]. Posaconazole can be taken with or without food depending on the formulation (suspension, tablet, or intravenous), so follow the specific instructions on your prescription [12]. Avoid drinking grapefruit juice while taking tadalafil and posaconazole, as grapefruit also inhibits CYP3A4 and can further raise tadalafil levels, increasing the risk of side effects [4].

Limit alcohol intake, as heavy drinking can worsen erectile dysfunction, increase the risk of side effects such as dizziness and low blood pressure, and reduce the effectiveness of tadalafil [1][4]. If you experience a severe headache, dizziness, chest pain during sex, sudden vision or hearing loss, or an erection lasting more than four hours, stop taking tadalafil and seek urgent medical help [4]. Keep a list of all your medicines (including over-the-counter products and supplements) and share it with every healthcare professional you see, as this helps prevent harmful interactions.

Other antifungals and ED treatment: what you need to know

Posaconazole is not the only antifungal that interacts with tadalafil and other PDE5 inhibitors. Ketoconazole and itraconazole are also potent CYP3A4 inhibitors and require the same dose reductions for tadalafil [4]. Fluconazole is a moderate CYP3A4 inhibitor and may also raise tadalafil levels, though usually to a lesser extent; your prescriber will still review the combination and may adjust your dose [4][12]. Topical antifungals (creams, pessaries) are unlikely to interact because very little is absorbed into the bloodstream, but always mention them during your consultation.

If you are prescribed vardenafil (Levitra) or avanafil (Spedra) instead of tadalafil, be aware that these PDE5 inhibitors are even more sensitive to CYP3A4 inhibition [5][6]. Vardenafil and avanafil are contraindicated or not recommended with potent inhibitors such as posaconazole, ketoconazole, itraconazole, ritonavir, and cobicistat [5][6]. Sildenafil (Viagra) can be used with dose adjustment (a maximum of 25 mg in 48 hours), but your prescriber must confirm this is safe for you [3]. At Cured Pharmacy, every prescription for erectile dysfunction is reviewed by a UK-registered prescriber who checks your current medicines and health conditions to ensure the treatment is safe and appropriate for you.

When to see your GP

If you develop new or worsening erectile dysfunction, especially if you have not been assessed by a doctor before, book an appointment with your GP [1][2]. ED can be an early warning sign of cardiovascular disease, diabetes, or other health conditions that need investigation and treatment [1][10]. Your GP can arrange blood tests, check your blood pressure, review your medicines, and refer you to a specialist if needed. If you experience chest pain, severe dizziness, fainting, or any other concerning symptoms while taking tadalafil and posaconazole, seek medical help immediately.

When to get urgent help

• Erection lasting more than 4 hours (priapism)—go to A&E immediately to prevent permanent damage
• Sudden loss of vision or hearing—stop tadalafil and seek same-day medical help
• Chest pain during sex—stop activity, do not take more tadalafil, and call 999 if pain does not resolve quickly
• Severe dizziness, fainting, or signs of very low blood pressure—lie down, seek urgent help, and tell them you take tadalafil and posaconazole
• 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.

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