Tadalafil and Valaciclovir: Can You Take Them Together?

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Key takeaways

• No major interaction is commonly reported between tadalafil and valaciclovir
• Both medicines can generally be taken together without separating doses
• Always declare all current medicines during your consultation
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers
• See your GP for new ED as it can signal heart disease or diabetes

What is tadalafil and what is it 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 the active ingredient in Cialis and is available as a generic medicine at lower cost.

Tadalafil comes in two forms: on-demand tablets (10mg or 20mg) taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours, and daily tablets (2.5mg or 5mg) taken once a day at the same time [4]. Both forms require sexual stimulation to work. Tadalafil does not cure ED but can help you achieve and maintain an erection sufficient for sexual activity when used as directed.

At Cured Pharmacy, tadalafil is available on prescription after an online consultation reviewed by a UK-registered prescriber. Common side effects include headache, indigestion, back pain, and flushing, which are usually mild and temporary [4].

What is valaciclovir and what is it used for?

Valaciclovir is an antiviral prescription medicine used to treat infections caused by herpes viruses, including genital herpes, cold sores, and shingles (herpes zoster). It works by stopping the virus from multiplying, which helps to reduce the severity and duration of outbreaks and can also be used to prevent recurrent episodes.

When you take valaciclovir, it is converted in the body to aciclovir, the active antiviral substance. It is most effective when started as soon as symptoms appear. Valaciclovir is generally well tolerated, with common side effects including headache, nausea, and dizziness. It is processed mainly by the kidneys, so dose adjustments may be needed if you have kidney problems.

Valaciclovir does not interact with the way tadalafil works in the body. The two medicines are processed differently and do not share the same metabolic pathways, meaning they are unlikely to affect each other's levels or effectiveness. However, it is still essential to tell your prescriber about all medicines you are taking, including antivirals, during your consultation.

At a glance

Can you take tadalafil and valaciclovir together?

Yes, tadalafil and valaciclovir can generally be taken together. No major interaction is commonly reported between these two medicines, and they work through different mechanisms in the body. Tadalafil affects blood flow to the penis by inhibiting the PDE5 enzyme, while valaciclovir stops viral replication. Neither medicine is known to significantly alter the levels or effects of the other.

However, every person's medical situation is unique. During your online consultation at Cured Pharmacy, you will be asked to list all current medicines, including valaciclovir, so that the prescriber can review your full medication list and check for any potential issues. This is a standard safety step for all prescription treatments.

You should not stop or change your valaciclovir treatment without consulting the doctor who prescribed it. If you are taking valaciclovir for a current outbreak or as suppressive therapy, continue as directed. If you have any concerns about taking both medicines, speak to your GP, prescriber, or pharmacist for personalised advice.

What your prescriber will check

When you request tadalafil, the prescriber will review your full medical history, including any heart conditions, blood pressure, kidney or liver problems, and all current medicines. They will check that tadalafil is safe for you and that there are no contraindications or significant interactions with your other treatments, including valaciclovir. This consultation ensures that the dose and timing are appropriate for your individual circumstances.

Medicines that do interact with tadalafil

While tadalafil and valaciclovir do not interact, there are important medicines that you must never take with tadalafil. Do not take tadalafil if you are using nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, or amyl/alkyl nitrites (poppers). Combining tadalafil with any of these can cause a dangerous drop in blood pressure [4].

Do not take tadalafil with another PDE5 inhibitor (such as sildenafil, vardenafil, or avanafil) at the same time. If you are taking alpha-blockers for prostate problems or high blood pressure (such as doxazosin, tamsulosin, or alfuzosin), there is a risk of low blood pressure and dizziness. You should be stable on the alpha-blocker before starting tadalafil, and your prescriber will usually recommend the lowest dose initially [4].

Certain medicines that affect liver enzymes can raise tadalafil levels in the blood. Potent CYP3A4 inhibitors—including ritonavir, cobicistat, Paxlovid, ketoconazole, itraconazole, and clarithromycin—may require a reduced maximum dose of tadalafil [4]. Conversely, CYP3A4 inducers such as rifampicin, carbamazepine, phenytoin, and St John's wort can make tadalafil less effective. Always declare every medicine, supplement, and herbal remedy during your consultation.

Practical advice for taking tadalafil and valaciclovir

If you are prescribed both tadalafil and valaciclovir, you can take them on the same day without needing to separate the doses by a specific time interval. There is no evidence that one medicine affects the absorption or effectiveness of the other. Follow the dosing instructions for each medicine as directed by your prescriber.

For on-demand tadalafil, take one tablet at least 30 minutes before sexual activity, with effects lasting up to 36 hours. For daily tadalafil, take one tablet at the same time each day. Valaciclovir is usually taken two or three times a day for treatment of an outbreak, or once or twice daily for suppressive therapy, depending on your prescription. You can take both medicines with or without food.

Avoid drinking excessive alcohol when taking tadalafil, as heavy drinking can worsen erectile dysfunction and add to the blood-pressure-lowering effect, increasing the risk of dizziness [4]. Grapefruit juice can raise tadalafil levels and should be avoided. If you experience side effects from either medicine, or if you have any concerns, contact your prescriber or pharmacist for advice.

When to seek medical advice

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 tadalafil [4]. If you develop severe side effects from valaciclovir, such as confusion, hallucinations, or signs of kidney problems (reduced urination, swelling), contact your doctor immediately. For new or worsening erectile dysfunction, see your GP, as ED can be an early sign of heart disease or diabetes [1].

How to get tadalafil safely online in the UK

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

We offer a range of ED treatments, including generic tadalafil and branded Cialis, as well as sildenafil, vardenafil, and avanafil. All treatments require a prescription, and our clinical team is available to answer any questions about your medicines. You should always declare every medicine you are taking, including over-the-counter products and supplements, during your consultation.

If you have not been assessed for ED before, or if your symptoms have changed, we encourage you to see your GP for a full evaluation. Erectile dysfunction can be an early warning sign of cardiovascular disease or diabetes, and addressing the underlying cause is an important part of treatment [1][2]. Our service is designed to provide convenient access to treatment once a diagnosis has been made and you know which medicine works for you.

Choosing the right ED treatment

Tadalafil is popular because of its long duration of action (up to 36 hours), which allows for more spontaneity compared to shorter-acting medicines like sildenafil [4]. However, the best ED treatment for you depends on your health, preferences, and how you respond to the medicine. Your prescriber can help you choose the most suitable option and adjust the dose if needed. All PDE5 inhibitors require sexual stimulation to work and do not increase sexual desire.

When to get urgent help

• Erection lasting more than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision or hearing while taking tadalafil – seek urgent medical help
• Chest pain during sexual activity – stop and call 999
• Severe dizziness or fainting after taking tadalafil – seek same-day medical advice

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