Tadalafil and Fosfomycin: Can You Take Them Together?

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What is tadalafil and fosfomycin used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction [4]. It works 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 option (2.5mg or 5mg) [4]. You may know it by the brand name Cialis, though generic versions are widely available and more affordable.

Fosfomycin is an antibiotic prescribed to treat uncomplicated urinary tract infections (UTIs), particularly in women, though it can be used in men as well. It is usually given as a single 3g sachet dissolved in water. Fosfomycin works by killing bacteria in the urinary tract. Because it is a short course (often just one dose), any potential interaction with other medicines is typically brief.

Is there an interaction between tadalafil and fosfomycin?

No major interaction is commonly reported between tadalafil and fosfomycin. These medicines work through different mechanisms in the body: tadalafil affects blood flow by inhibiting an enzyme called PDE5, while fosfomycin targets bacterial cell walls in the urinary tract. Neither medicine is known to significantly alter the metabolism or effectiveness of the other.

That said, every person's medical history is unique. Your prescriber or pharmacist will review all your current medicines, health conditions, and recent infections during your consultation to confirm that the combination is safe for you. This check is especially important if you are taking other medicines alongside tadalafil or fosfomycin, as those could introduce additional interactions.

Why your full medication list matters

Even when two medicines do not interact directly, other factors can affect safety. For example, if you are taking blood-pressure medicines or alpha-blockers for prostate symptoms, tadalafil can add to their blood-pressure-lowering effect, causing dizziness [4]. Similarly, some antibiotics (though not fosfomycin) can interact with tadalafil by affecting how your liver breaks it down. Always declare every medicine, supplement, and over-the-counter product you use, including any recent courses of antibiotics.

When to get urgent help

• Erection lasting more than 4 hours (priapism) – go to A&E immediately
• Sudden loss of vision or hearing – seek urgent medical help
• Chest pain during or after sex – call 999
• Severe dizziness or fainting after taking tadalafil – contact your GP or call 111
• Blood in urine with fever and back pain (possible kidney infection) – see your GP the same day or call 111

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

What does your prescriber check before approving tadalafil and fosfomycin?

When you request tadalafil through an online consultation at Cured Pharmacy, a UK-registered prescriber reviews your medical history, current medicines, and any recent infections or treatments. They will check that tadalafil is not contraindicated for you—for instance, you must not take it if you use nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs called poppers, because the combination can cause a dangerous drop in blood pressure [3][4].

If you mention that you are taking or have recently taken fosfomycin for a UTI, the prescriber will note this but will typically find no reason to withhold tadalafil on that basis alone. They will, however, ensure that any other medicines you are taking do not pose a risk. For example, potent CYP3A4 inhibitors (such as ritonavir, ketoconazole, or clarithromycin) can raise tadalafil levels, requiring a lower dose [4]. The prescriber may also ask about your cardiovascular health, as sexual activity itself can strain the heart in people with severe heart disease [2].

Practical advice for taking tadalafil and fosfomycin together

If your doctor or pharmacist has confirmed that both medicines are suitable for you, you can take them as prescribed without special timing restrictions. Fosfomycin is usually a single dose, so any overlap with tadalafil will be brief. Take fosfomycin on an empty stomach (ideally before bed, after emptying your bladder) to maximise its effectiveness against the UTI. Tadalafil can be taken with or without food, though a very heavy or fatty meal may delay its onset slightly [4].

Continue to follow the dosing instructions for each medicine. For on-demand tadalafil, take one tablet at least 30 minutes before sexual activity, and do not take more than one dose in 24 hours [4]. If you are on daily tadalafil, take it at the same time each day. Finish the full course of any antibiotic as directed, even if your symptoms improve quickly. If you experience any unexpected side effects—such as severe dizziness, prolonged erection (lasting more than four hours), or sudden vision or hearing loss—seek medical help immediately.

Staying hydrated and monitoring side effects

Both UTIs and antibiotics can cause mild side effects such as nausea or stomach upset. Drink plenty of water to help flush bacteria from your urinary tract and to stay hydrated, especially if you experience any gastrointestinal symptoms. Tadalafil's common side effects include headache, indigestion, back pain, and flushing [4]. These are usually mild and temporary. If you notice anything unusual or concerning, contact your GP or pharmacist for advice.

At a glance

When tadalafil and fosfomycin should not be used

Do not take tadalafil if you are using nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or poppers (amyl or alkyl nitrites), as the combination can cause a dangerous fall in blood pressure [3][4]. Tadalafil is also not suitable if you have recently had a heart attack or stroke, have unstable angina, severe heart failure, very low blood pressure, or a history of non-arteritic anterior ischaemic optic neuropathy (sudden vision loss) [4].

Fosfomycin should not be used if you have severe kidney problems or are allergic to it. If you have a complicated UTI (such as one involving the kidneys or accompanied by fever and back pain), fosfomycin may not be the right choice, and you should see your GP for a full assessment. Never take another PDE5 inhibitor (such as sildenafil, vardenafil, or avanafil) at the same time as tadalafil [3][4].

How to access tadalafil and fosfomycin safely in the UK

Both tadalafil and fosfomycin are prescription-only medicines in the UK. At Cured Pharmacy, you can request tadalafil through a confidential online consultation. A UK-registered prescriber will review your answers and, if appropriate, approve your prescription. Tadalafil is then dispensed by our GPhC-registered pharmacy and delivered discreetly to your door. Generic tadalafil starts from £7.95, or £6.36 for your first order with code Ednew.

Fosfomycin is typically prescribed by your GP or a sexual health clinic for a diagnosed UTI. If you develop symptoms of a UTI (such as pain or burning when urinating, frequent urination, or cloudy urine), see your GP or use an NHS online consultation service. Do not stop or change any prescribed medicine without professional advice. If you have new or worsening erectile dysfunction, it is important to see your GP, as ED can be an early sign of heart disease or diabetes [1][2].

Why choose Cured Pharmacy for tadalafil

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering a range of ED treatments, including tadalafil, sildenafil, vardenafil, and avanafil. Every prescription is reviewed by a UK-registered prescriber, and our pharmacists are available to answer your questions. We provide clear information, discreet packaging, and fast delivery, so you can access the treatment you need with confidence.

In summary

• No major interaction is commonly reported between tadalafil and fosfomycin
• Your prescriber checks your full medication list to confirm the combination is safe
• Tadalafil must not be taken with nitrates, nicorandil, riociguat, or poppers
• Both medicines are prescription-only and require clinical assessment in the UK
• Always declare all current medicines, including recent antibiotics, during your consultation

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