Tadalafil and Leflunomide: Can They Be Taken Together?

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At a glance

What is tadalafil and leflunomide used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED) [3][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 (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 option (2.5 mg or 5 mg) [4]. You may know tadalafil by its brand name, Cialis, though generic versions are widely available and work in exactly the same way.

Leflunomide is a disease-modifying antirheumatic drug (DMARD) prescribed to manage rheumatoid arthritis and psoriatic arthritis [12]. It works by suppressing the overactive immune response that causes joint inflammation and damage. Leflunomide is taken once daily as a long-term treatment and requires regular blood test monitoring to check liver function and blood counts. Because it affects the immune system, your doctor will have considered your overall health carefully before prescribing it.

Both medicines serve very different purposes, but it is entirely normal to need treatment for more than one condition. Understanding how they might interact—or reassuringly, how they do not—helps you use both safely and confidently.

Is there an interaction between tadalafil and leflunomide?

No major direct pharmacological interaction between tadalafil and leflunomide is commonly reported in UK clinical practice or the British National Formulary [3][4]. This means that the two medicines do not interfere with each other's breakdown in the body or significantly alter each other's effects in a way that would make the combination unsafe for most people.

Tadalafil is primarily broken down by an enzyme called CYP3A4 in the liver [4]. Leflunomide does not strongly inhibit or induce this enzyme, so it is unlikely to raise or lower tadalafil levels in your bloodstream. Similarly, leflunomide's own metabolism is not significantly affected by tadalafil. This is why many men with rheumatoid or psoriatic arthritis who are stable on leflunomide are able to use tadalafil for erectile dysfunction without problems.

That said, 'no major interaction' does not mean the combination is automatically suitable for everyone. Your prescriber will still review your full medical history, current medicines (including leflunomide), blood pressure, heart health, and any other conditions during your consultation. This careful assessment ensures that tadalafil is the right choice for you personally, even if the interaction risk with leflunomide itself is low.

Why your prescriber still checks every medicine

Even when two medicines do not interact directly, your prescriber must consider the bigger picture. For example, some people taking leflunomide may also be on other medicines—such as blood pressure tablets or pain relief—that could interact with tadalafil. Additionally, both leflunomide and tadalafil can, in rare cases, affect blood pressure or liver function, so your prescriber will review recent blood test results and your cardiovascular health. This holistic approach ensures your safety and helps avoid any unexpected side effects.

What does your prescriber check before prescribing tadalafil?

When you request tadalafil through Cured Pharmacy, a UK-registered prescriber reviews your online consultation answers carefully [2]. They will ask about all your current medicines, including leflunomide, to check for any interactions or contraindications. They will also ask about your heart health, blood pressure, any history of stroke or heart attack, liver or kidney function, and whether you have conditions such as diabetes or high cholesterol that can contribute to ED [1][2].

Certain medicines must never be taken with tadalafil because they can cause a dangerous drop in blood pressure. These include nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, and recreational drugs called 'poppers' (amyl or alkyl nitrites) [3][4]. If you take any of these, do not take tadalafil. Your prescriber will also check whether you are on alpha-blockers (such as tamsulosin or doxazosin) for prostate symptoms, as these can add to the blood-pressure-lowering effect of tadalafil; if so, you will usually start on the lowest dose [4].

If you are taking medicines that strongly inhibit the enzyme CYP3A4—such as ritonavir, cobicistat, ketoconazole, itraconazole, or clarithromycin—your prescriber may need to adjust your tadalafil dose or choose a different ED treatment [4]. Leflunomide is not a strong CYP3A4 inhibitor, so this particular concern does not apply. Your prescriber will also consider your overall fitness for sexual activity, as sex is a form of physical exertion that may not be safe if you have severe heart problems or very low blood pressure [2].

What you need to know

• No major interaction between tadalafil and leflunomide is commonly reported in UK clinical practice.
• Your prescriber reviews all your medicines, including leflunomide, during your consultation to ensure tadalafil is safe.
• Continue your leflunomide as prescribed and take tadalafil as directed by your prescriber.
• Seek urgent help if you have chest pain during sex, an erection over four hours, or sudden vision or hearing loss.
• New erectile dysfunction should be checked by your GP to rule out heart disease or diabetes.

Practical advice for taking tadalafil and leflunomide together

If your prescriber approves tadalafil, continue taking your leflunomide exactly as prescribed by your rheumatologist or GP. Do not stop or change the dose of leflunomide without medical advice, as this could cause your arthritis to flare. Take tadalafil as directed: on-demand tablets (10 mg or 20 mg) should be taken at least 30 minutes before sexual activity, while daily tablets (2.5 mg or 5 mg) are taken once a day at the same time [4]. Tadalafil requires sexual stimulation to work—it will not cause an erection on its own.

Avoid drinking large amounts of alcohol when using tadalafil, as heavy drinking can worsen erectile dysfunction and increase the risk of dizziness or low blood pressure [3][4]. Grapefruit juice can raise tadalafil levels in your 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 [4]. 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.

Keep all your routine appointments for blood tests and check-ups related to leflunomide. Your rheumatology team will continue to monitor your liver function and blood counts, and it is important to tell them you are also taking tadalafil so they have a complete picture of your medicines. If you notice any new symptoms or have concerns, speak to your GP, pharmacist, or the Cured Pharmacy clinical team—never simply stop a prescribed medicine without advice.

When to speak to your doctor

If erectile dysfunction is a new problem for you, see your GP before requesting treatment online. ED can be an early warning sign of cardiovascular disease or diabetes, and your doctor may want to check your blood pressure, cholesterol, and blood sugar levels [1][2]. If tadalafil does not work for you, or if your ED worsens, arrange a follow-up appointment. Your GP or a specialist can explore other treatment options, including different PDE5 inhibitors, vacuum devices, or referral to a sexual health or urology clinic.

Other medicines and conditions to consider with tadalafil

While tadalafil and leflunomide do not interact significantly, other medicines you take may affect tadalafil's safety or effectiveness. Alpha-blockers (such as tamsulosin, doxazosin, or alfuzosin) are commonly prescribed for prostate symptoms and can add to tadalafil's blood-pressure-lowering effect, causing dizziness or fainting [4]. If you take an alpha-blocker, your prescriber will usually start you on the lowest dose of tadalafil and ensure you are stable on the alpha-blocker first.

Medicines that strongly inhibit the liver enzyme CYP3A4—including HIV protease inhibitors (ritonavir, cobicistat), antifungals (ketoconazole, itraconazole), and some antibiotics (clarithromycin)—can raise tadalafil levels, increasing the risk of side effects [4]. Your prescriber may reduce your tadalafil dose or recommend a different ED treatment if you are on one of these medicines. Conversely, enzyme inducers such as rifampicin, carbamazepine, phenytoin, or St John's wort can make tadalafil less effective by speeding up its breakdown [4].

Tadalafil is not suitable if you have been advised to avoid sexual activity due to severe heart problems, such as unstable angina, recent heart attack or stroke, or severe heart failure [2][4]. It is also contraindicated if you have very low blood pressure, a history of non-arteritic anterior ischaemic optic neuropathy (NAION, a rare cause of sudden vision loss), or certain inherited retinal disorders [4]. Your prescriber will assess all these factors during your consultation to ensure tadalafil is safe for you.

When to get urgent help

• Erection lasting more than four hours (priapism) – go to A&E immediately
• Sudden loss of vision in one or both eyes – stop tadalafil and seek urgent medical help
• Sudden decrease or loss of hearing, sometimes with ringing in the ears or dizziness – seek urgent advice
• Chest pain during or after sex – call 999 and do not take more tadalafil
• Severe dizziness, fainting, or very low blood pressure – seek same-day medical attention

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

How to access tadalafil safely through Cured Pharmacy

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering convenient access to erectile dysfunction treatments, including tadalafil, after a clinical consultation reviewed by a UK-registered prescriber. To request tadalafil, complete a short online health questionnaire that asks about your medical history, current medicines (including leflunomide), and any conditions that might affect your suitability for treatment. A prescriber will review your answers carefully and, if appropriate, approve your prescription.

Once approved, your medicine is dispensed by our pharmacy team and delivered discreetly to your home. We offer a range of tadalafil options, including generic tadalafil from £7.95 (or £6.36 for first orders with code Ednew), branded Cialis from £12.00 (£9.60 with code Ednew), and Teva tadalafil 20 mg from £9.99 (£7.99 with code Ednew). All our medicines are sourced from licensed UK wholesalers and meet MHRA quality standards. If you have questions about your treatment or need advice, our pharmacist-led team is here to help.

Remember, tadalafil is a prescription-only medicine, and online consultations are not a substitute for seeing your GP, especially if ED is a new symptom. If you have not already done so, arrange a check-up with your doctor to rule out underlying health conditions such as diabetes or heart disease [1][2]. Treating ED is important, but so is understanding and managing its causes.

Why choose Cured Pharmacy for your ED treatment?

Cured Pharmacy combines clinical expertise with convenience. Every prescription is reviewed by a UK-registered prescriber, ensuring your safety and peace of mind. Our service is discreet, affordable, and designed to fit around your life. Whether you are taking leflunomide, managing other long-term conditions, or simply looking for a straightforward way to access ED treatment, we are here to support you with professional, non-judgemental care.