Can You Take Tadalafil and Penicillin V Together?

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Tadalafil and Penicillin V: Understanding the Interaction

Published: 24 October 2026

Many men wonder whether tadalafil and penicillin V can be taken together safely. The good news is that no major interaction is commonly reported between tadalafil (a medicine for erectile dysfunction) and penicillin V (an antibiotic used to treat bacterial infections). However, your prescriber will still review all your current medicines during your consultation to ensure the combination is appropriate for you personally.

What is tadalafil and penicillin V?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. 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 [3][4]. Tadalafil is the active ingredient in branded Cialis and is available in generic forms. It can be taken on-demand (10 mg or 20 mg 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) [4].

Penicillin V (also called phenoxymethylpenicillin) is an antibiotic used to treat bacterial infections such as throat infections, tonsillitis, ear infections, and some skin infections. It works by killing bacteria or stopping them from multiplying. Penicillin V is usually taken two to four times a day for a course of several days, depending on the type and severity of the infection. It does not interact with the way tadalafil works in the body.

Do tadalafil and penicillin V interact with each other?

No major interaction is commonly reported between tadalafil and penicillin V. These two medicines work through completely different mechanisms in the body. Tadalafil affects an enzyme (PDE5) involved in blood flow to the penis, while penicillin V targets bacterial cell walls to fight infection [3][4]. Neither medicine is known to significantly affect the breakdown or effectiveness of the other.

However, it is still important to tell your prescriber or pharmacist about all medicines you are taking, including antibiotics. During your online consultation at Cured Pharmacy, the prescriber will review your full medication list to check for any potential issues. While penicillin V itself does not interact with tadalafil, some other antibiotics (such as clarithromycin or erythromycin) can raise tadalafil levels in the blood and may require dose adjustments [4].

How the combination is assessed

Your prescriber will check that tadalafil is safe for you by reviewing your medical history, current medicines, and any underlying health conditions. They will ensure you are not taking any medicines that are known to interact dangerously with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called 'poppers' [3][4]. If you are taking penicillin V for a short course, this will not prevent you from using tadalafil, provided you are otherwise suitable for ED treatment.

What your prescriber checks before prescribing tadalafil

Before prescribing tadalafil, your prescriber will ask about your general health, heart and blood pressure history, and all medicines you currently take (including over-the-counter products and herbal supplements). This is to identify any conditions or medicines that could make tadalafil unsuitable or require a lower starting dose [2][4].

Tadalafil is not suitable if you take nitrates for angina, nicorandil, riociguat for pulmonary hypertension, or another PDE5 inhibitor at the same time. Do not take these medicines together, as the combination can cause a dangerous drop in blood pressure [3][4]. Your prescriber will also check if you take alpha-blockers (such as tamsulosin or doxazosin) for prostate or blood pressure problems, as these can add to the blood-pressure-lowering effect of tadalafil; if you do, you should be stable on the alpha-blocker and start on the lowest dose of tadalafil.

Other important checks include whether you have had a recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (NAION). If you have any of these conditions, tadalafil may not be safe for you [4]. The prescriber will also ask about liver or kidney problems, as dose adjustments may be needed.

Practical advice when taking tadalafil and penicillin V together

If you have been prescribed both tadalafil and penicillin V, you can usually take them together without concern. There is no need to separate the doses or avoid taking them on the same day. Continue to take your penicillin V exactly as prescribed by your doctor, completing the full course even if you start to feel better, to ensure the infection is fully treated.

Take tadalafil as directed: if you are using the on-demand dose (10 mg or 20 mg), take it at least 30 minutes before you plan to have sex. The effect can last up to 36 hours, so you do not need to take another dose within that time [4]. If you are on a daily low dose (2.5 mg or 5 mg), take it at the same time each day, regardless of when you plan to have sex. Tadalafil will only work when you are sexually aroused; it does not cause an automatic erection.

Avoid drinking large amounts of alcohol, as this can make erectile dysfunction worse and increase the risk of dizziness or low blood pressure when combined with tadalafil [4]. Grapefruit juice can raise tadalafil levels in the blood, so it is best to avoid it. If you experience side effects such as headache, indigestion, back pain, or flushing, these are usually mild and temporary. If you develop an erection lasting more than four hours, sudden loss of vision or hearing, or chest pain during sex, seek urgent medical help.

Completing your antibiotic course

It is important to finish the full course of penicillin V, even if your symptoms improve before the medicine runs out. Stopping antibiotics early can allow the infection to return or contribute to antibiotic resistance. Taking tadalafil at the same time will not affect how well the antibiotic works, so you can continue your ED treatment as normal during and after your antibiotic course.

Warning signs and when to seek help with tadalafil and penicillin V

Most men tolerate tadalafil and penicillin V well, but it is important to know the warning signs that need urgent attention. If you develop an erection that lasts longer than four hours (priapism), go to A&E immediately or call 999. Priapism can damage the penis if not treated quickly [3][4].

Seek urgent medical help if you experience sudden loss of vision in one or both eyes, or sudden decrease or loss of hearing (which may be accompanied by ringing in the ears or dizziness). These are rare but serious side effects of PDE5 inhibitors [4]. If you develop chest pain during or after sex, stop sexual activity and seek medical advice; do not take nitrates (GTN spray) if you have used tadalafil in the past 48 hours, as this combination is dangerous.

If you develop signs of an allergic reaction to penicillin V—such as a rash, itching, swelling of the face or throat, or difficulty breathing—stop taking the antibiotic and seek immediate medical help. Penicillin allergy can be serious. If you experience severe or persistent diarrhoea during or after taking penicillin V, contact your GP, as this may indicate a bowel infection that needs different treatment.

Other medicines that interact with tadalafil

While penicillin V does not interact with tadalafil, several other medicines do require caution or are contraindicated. Never take tadalafil with nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites). These combinations can cause a dangerous drop in blood pressure [3][4].

Some medicines can raise tadalafil levels in the blood, increasing the risk of side effects. These include potent CYP3A4 inhibitors such as ritonavir, cobicistat (found in some HIV medicines), Paxlovid (used for COVID-19), ketoconazole and itraconazole (antifungal medicines), and clarithromycin and erythromycin (antibiotics). If you take any of these, your prescriber may recommend a lower dose of tadalafil or advise against using it [4].

Medicines that speed up the breakdown of tadalafil—such as rifampicin (an antibiotic for tuberculosis), carbamazepine and phenytoin (for epilepsy), and St John's wort (a herbal remedy)—can make tadalafil less effective. Other blood-pressure medicines can add to the blood-pressure-lowering effect of tadalafil, which is usually manageable but must be declared during your consultation [2][4]. Always tell your prescriber about every medicine you take, including over-the-counter products, vitamins, and herbal supplements.

Declaring all your medicines

During your online consultation at Cured Pharmacy, you will be asked to list all your current medicines. This is a vital safety check. Even if a medicine is not listed as a major interaction, your prescriber needs the full picture to make an informed decision. Do not stop or change any prescribed medicine without speaking to your doctor or pharmacist first.

Scientific References

1. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 24 October 2026]
2. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 24 October 2026]
3. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 24 October 2026]
4. NHS. (n.d.). Erectile dysfunction (impotence). https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ Accessed 24 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.

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