Tadalafil and Ketoconazole: Can They Be Taken Together?

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At a glance

What is tadalafil and ketoconazole used for?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men [4]. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused. Tadalafil is available as on-demand tablets (10mg or 20mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5mg or 5mg) for men who prefer spontaneity [4]. It requires sexual stimulation to work and does not increase sexual desire on its own.

Ketoconazole is an antifungal medicine used to treat serious fungal infections when other treatments have not worked or are unsuitable [12]. It is taken by mouth, usually once daily, and works by stopping fungi from producing a substance called ergosterol, which they need to survive. Because ketoconazole can affect the liver and interact with many other medicines, it is prescribed only when necessary and requires careful monitoring. It is not used for minor fungal infections such as athlete's foot or thrush, which are treated with safer topical or short-course antifungals.

How do tadalafil and ketoconazole interact?

Ketoconazole is a potent inhibitor of an enzyme in the liver called CYP3A4 [4]. This enzyme is responsible for breaking down tadalafil and clearing it from your body. When you take ketoconazole, it slows down this breakdown process, which means tadalafil stays in your bloodstream for longer and at higher levels than usual. This can make the effects of tadalafil stronger and increase the chance of side effects such as headache, flushing, indigestion, back pain, or a drop in blood pressure.

The interaction is predictable and well understood, so your prescriber can manage it by reducing the dose of tadalafil [4]. For men taking ketoconazole, the maximum recommended dose of tadalafil for on-demand use is 10mg within a 72-hour period, rather than the usual 20mg maximum per day. If you are taking daily tadalafil, your prescriber will review whether this is appropriate and may adjust the dose accordingly. It is essential that you tell your prescriber about all medicines you are taking, including antifungals, so they can calculate the safest dose for you.

Why CYP3A4 matters

CYP3A4 is one of the most important enzymes in the body for processing medicines. Many drugs—including tadalafil, some antibiotics, antifungals, HIV medicines, and even grapefruit juice—affect this enzyme. When a potent CYP3A4 inhibitor like ketoconazole is present, it can significantly alter how other medicines work. This is why your prescriber and pharmacist will always check for interactions during your consultation, and why you should never start a new medicine without declaring all your current treatments.

What your prescriber checks before prescribing tadalafil and ketoconazole together

During your online consultation at Cured Pharmacy, a UK-registered prescriber will review your full medical history and all current medicines, including ketoconazole [2]. They will check whether tadalafil is safe for you, considering your heart health, blood pressure, liver and kidney function, and any other conditions. If you are taking ketoconazole, the prescriber will adjust your tadalafil dose to account for the interaction, typically limiting you to a maximum of 10mg tadalafil in any 72-hour period [4].

The prescriber will also confirm that you are not taking any medicines that must never be combined with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or recreational drugs called poppers (amyl or alkyl nitrites). These combinations can cause a dangerous drop in blood pressure and must be avoided completely. If you take alpha-blockers for prostate symptoms or blood pressure (such as tamsulosin or doxazosin), the prescriber will ensure you are stable on that medicine and start you on the lowest effective dose of tadalafil.

You should also tell your prescriber if you have ever had sudden vision loss (a condition called NAION), severe heart problems, very low blood pressure, or a stroke or heart attack in the past six months, as tadalafil may not be suitable [4]. Being open and accurate about your health and medicines is the best way to ensure safe, effective treatment.

What you need to know

• Ketoconazole raises tadalafil levels by inhibiting the enzyme that breaks it down.
• Your prescriber will limit tadalafil to a maximum of 10mg in 72 hours if you take ketoconazole.
• Always declare all medicines during your consultation to ensure safe dose adjustments.
• Seek urgent help if you have chest pain, an erection over 4 hours, or sudden vision loss.

Practical advice for taking tadalafil with ketoconazole

If your prescriber has approved tadalafil while you are taking ketoconazole, follow the dose instructions carefully. Do not take more than the prescribed amount, and do not take tadalafil more often than advised—typically no more than 10mg in any 72-hour period if you are on ketoconazole [4]. Taking a higher dose or taking it more frequently will not improve your erection but will increase the risk of side effects such as headache, dizziness, flushing, or a drop in blood pressure.

Take your tadalafil tablet at least 30 minutes before you plan to have sex, and remember that you will need sexual stimulation for it to work [4]. The effects can last up to 36 hours, so you do not need to rush. Avoid drinking large amounts of alcohol, as this can make erectile dysfunction worse and add to the blood-pressure-lowering effect of tadalafil. Grapefruit juice can also raise tadalafil levels, so it is best avoided while you are on this combination.

If you experience side effects that are troublesome or do not go away, contact your prescriber or pharmacist for advice. Common side effects include headache, indigestion, back pain, muscle aches, and facial flushing, which usually settle on their own. However, if you develop chest pain during sex, an erection lasting more than four hours, or sudden loss of vision or hearing, seek urgent medical help immediately.

What if I need to start or stop ketoconazole?

If you are already taking tadalafil and your doctor prescribes ketoconazole, tell both your GP and your ED prescriber straight away. Your tadalafil dose will need to be reviewed and reduced to avoid high levels building up. Similarly, if you finish a course of ketoconazole, your prescriber may be able to increase your tadalafil dose back to the standard amount. Never adjust your doses yourself—always check with a healthcare professional first.

Other medicines that interact with tadalafil in a similar way

Ketoconazole is not the only medicine that inhibits CYP3A4 and raises tadalafil levels. Other potent CYP3A4 inhibitors include itraconazole (another antifungal), clarithromycin and erythromycin (antibiotics), ritonavir and cobicistat (used in HIV treatment), and Paxlovid (used for COVID-19) [3][4]. If you are taking any of these medicines, your prescriber will apply similar dose restrictions to keep you safe.

On the other hand, some medicines speed up the CYP3A4 enzyme and can make tadalafil less effective. These include rifampicin (an antibiotic for tuberculosis), carbamazepine and phenytoin (for epilepsy), and the herbal remedy St John's wort [4]. If you take any of these, tadalafil may not work as well, and your prescriber may need to consider an alternative treatment or adjust your plan.

Alpha-blockers such as tamsulosin, doxazosin, alfuzosin, and terazosin are commonly prescribed for prostate symptoms or high blood pressure. They can add to the blood-pressure-lowering effect of tadalafil, causing dizziness or fainting, especially when you stand up [4]. If you take an alpha-blocker, you should be stable on it before starting tadalafil, and your prescriber will start you on the lowest dose. Always declare every medicine you take—including over-the-counter products, vitamins, and herbal remedies—during your consultation.

When to get urgent help

• Chest pain during or after sex—call 999 immediately
• Erection lasting more than 4 hours (priapism)—go to A&E
• Sudden loss of vision or hearing—seek urgent medical help
• Severe dizziness or fainting after taking tadalafil—call 999 or go to A&E

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

When to seek medical help and how Cured Pharmacy can support you

Seek urgent medical help (call 999 or go to A&E) if you experience chest pain during sex, an erection lasting more than four hours (priapism), or sudden loss of vision or hearing while taking tadalafil [4]. These are rare but serious side effects that need immediate attention. If you feel dizzy, faint, or unwell after taking tadalafil, sit or lie down and avoid driving or operating machinery. Contact your GP or NHS 111 for advice if symptoms persist.

At Cured Pharmacy, a GPhC-registered online pharmacy (GPhC 9012511), you can request tadalafil and other erectile dysfunction treatments through a confidential online consultation. A UK-registered prescriber will review your medical history, current medicines (including ketoconazole), and overall health to ensure tadalafil is safe and appropriate for you. If approved, your medicine is dispensed by our qualified pharmacists and delivered discreetly to your door.

We offer a range of ED treatments to suit different needs and budgets, including generic tadalafil from £7.95 (£6.36 with first-order code Ednew), branded Cialis from £12.00 (£9.60 with code Ednew), and other options such as sildenafil, vardenafil, and avanafil. Our team is here to answer your questions and support you at every step. If you have new or worsening erectile dysfunction, we encourage you to see your GP as well, as ED can be an early sign of heart disease or diabetes [1][2].

Why choose Cured Pharmacy?

Cured Pharmacy combines clinical expertise with convenience and discretion. Every prescription is reviewed by a UK-registered prescriber and dispensed by experienced pharmacists. We are fully regulated by the General Pharmaceutical Council, so you can trust that your treatment is safe, legal, and tailored to your individual needs. Our online service saves you time while giving you access to the same high standards of care you would expect from any registered UK pharmacy.