Sildenafil and Ustekinumab: Can They Be Taken Together?

Sildenafil and Ustekinumab: Understanding the Interaction

Published: 18 October 2026

If you're prescribed ustekinumab for psoriasis, Crohn's disease or ulcerative colitis and are considering sildenafil for erectile dysfunction, you may wonder whether sildenafil and ustekinumab can be taken together safely. The good news is that no major interaction between these two medicines is commonly reported in clinical practice. However, every person's medical history is unique, and your prescriber will review all your current medicines during a consultation to ensure sildenafil is suitable for you.

What Is Sildenafil and How Does It Work?

Sildenafil is a medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing the blood vessels in the penis, allowing more blood to flow in when you are sexually aroused [3]. Sildenafil is the active ingredient in Viagra and is available in generic forms at lower cost.

The medicine is typically taken about one hour before sexual activity, and its effects can last for around four to six hours. It's important to understand that sildenafil does not cause an erection on its own—sexual stimulation is still needed for it to work [1]. Common doses are 25mg, 50mg and 100mg, with 50mg being the usual starting dose for most men.

Sildenafil is a prescription-only medicine in the UK (except for the 50mg pharmacy version, Viagra Connect, which can be supplied by a pharmacist after a consultation). At Cured Pharmacy, all prescription ED treatments are supplied following an online consultation reviewed by a UK-registered prescriber to ensure they are safe and suitable for you.

What Is Ustekinumab and Why Is It Prescribed?

Ustekinumab is a biologic medicine used to treat certain inflammatory conditions, including moderate to severe plaque psoriasis, psoriatic arthritis, Crohn's disease and ulcerative colitis. It works by targeting specific proteins in the immune system (interleukin-12 and interleukin-23) that contribute to inflammation.

Ustekinumab is given by injection under the skin, usually every 8 or 12 weeks after initial loading doses, depending on the condition being treated. Because it affects the immune system, your doctor will monitor you for infections and other potential side effects. It is a long-term treatment that helps control symptoms and reduce flare-ups of inflammatory disease.

Many men with psoriasis or inflammatory bowel disease also experience erectile dysfunction, which can be related to the condition itself, the psychological impact of living with a chronic illness, or other health factors such as diabetes or cardiovascular disease [10]. Treating ED can be an important part of overall wellbeing and quality of life.

Can Inflammatory Conditions Affect Erectile Function?

Yes, chronic inflammatory conditions such as psoriasis and inflammatory bowel disease have been associated with a higher risk of erectile dysfunction. Inflammation in the body can affect blood vessel health, and the psychological burden of managing a long-term condition can also contribute to ED [10]. Addressing ED with appropriate treatment can improve confidence and quality of life.

Sildenafil and Ustekinumab: Is There an Interaction?

No major interaction between sildenafil and ustekinumab is commonly reported in clinical practice or the British National Formulary [3]. Ustekinumab is a biologic that targets immune pathways and does not significantly affect the liver enzymes (such as CYP3A4) that break down sildenafil. Similarly, sildenafil does not interfere with the way ustekinumab works in the immune system.

However, it is essential to declare all your current medicines—including ustekinumab and any other treatments for psoriasis, inflammatory bowel disease or other conditions—when you request sildenafil. Your prescriber will review your full medical history to check for any individual factors that might affect suitability, such as cardiovascular health, blood pressure or other medicines you are taking.

While the combination of sildenafil and ustekinumab is not known to cause problems, your prescriber may ask about your overall health, including any heart or blood vessel conditions, because ED can sometimes be an early sign of cardiovascular disease [1]. This holistic review ensures that sildenafil is safe and appropriate for you.

What Your Prescriber Checks Before Approving Sildenafil

When you request sildenafil through Cured Pharmacy, a UK-registered prescriber will review your online consultation to ensure the medicine is safe for you. They will check your current medicines, including ustekinumab, and look for any that could interact dangerously with sildenafil. Medicines you must never take with sildenafil include nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat and recreational drugs called 'poppers' [3]. Taking sildenafil with any of these can cause a dangerous drop in blood pressure.

Your prescriber will also ask about alpha-blockers (such as tamsulosin or doxazosin), which are used for prostate problems or high blood pressure. If you take an alpha-blocker, you can usually still use sildenafil, but you should be stable on the alpha-blocker first and start on the lowest dose of sildenafil to reduce the risk of dizziness or fainting [3].

Other important checks include your cardiovascular health (recent heart attack, stroke, unstable angina or severe heart failure), blood pressure, and any history of sudden vision or hearing loss. If you have any of these conditions, sildenafil may not be suitable, or you may need closer monitoring [1][3]. The prescriber will also review any other blood-pressure medicines you take, as these can add to the blood-pressure-lowering effect of sildenafil.

Medicines That Raise Sildenafil Levels

Some medicines slow down the breakdown of sildenafil in the body, which can increase its levels and 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, itraconazole and clarithromycin [3]. If you take any of these, your prescriber may recommend a lower starting dose of sildenafil or suggest an alternative ED treatment. Always declare every medicine you are taking, including over-the-counter and herbal products.

Practical Advice for Taking Sildenafil and Ustekinumab Together

If your prescriber approves sildenafil, you can take it as directed while continuing your ustekinumab treatment. Take sildenafil about one hour before you plan to have sex, on an empty stomach or after a light meal, as a heavy or high-fat meal can delay its effect [3]. You should not take sildenafil more than once in 24 hours.

Common side effects of sildenafil include headache, flushing, indigestion and nasal congestion. These are usually mild and short-lived [3]. If you experience dizziness or light-headedness, sit or lie down until it passes, and avoid driving or operating machinery. Drinking large amounts of alcohol can make ED worse and increase the risk of side effects such as dizziness, so it's best to limit alcohol when using sildenafil [1].

Continue taking ustekinumab exactly as your specialist has prescribed. Do not stop or change the dose of any medicine without speaking to your doctor or pharmacist. If you develop any new symptoms or side effects, or if sildenafil does not work as expected, contact your prescriber or GP for advice. Remember, sildenafil treats the symptom of ED but does not address the underlying cause, so it's important to see your GP if you have new or worsening erectile dysfunction, as it can be an early sign of heart disease or diabetes [1][2].

When to Seek Urgent Help and Warning Signs with Sildenafil

Most men tolerate sildenafil well, but you should be aware of warning signs that need urgent medical attention. If you have an erection that lasts longer than four hours (priapism), go to A&E immediately, as this can cause permanent damage to the penis [3]. Priapism is rare but requires emergency treatment.

Seek urgent help if you experience sudden loss of vision in one or both eyes, as this could be a sign of a serious condition called non-arteritic anterior ischaemic optic neuropathy (NAION) [3]. Similarly, sudden hearing loss or ringing in the ears requires immediate medical assessment. If you develop chest pain during or after sex, do not take more sildenafil—call 999 or go to A&E, especially if the pain spreads to your arms, neck or jaw, as this could indicate a heart problem [1].

If you experience severe dizziness, fainting or an allergic reaction (such as swelling of the face, lips or throat, or difficulty breathing), seek emergency help straight away. These reactions are uncommon but require immediate treatment. Always keep your prescriber and GP informed of any new symptoms or concerns, and never take sildenafil if you have been told to avoid sexual activity due to heart problems.

Can I Take Sildenafil with Other ED Medicines?

No, you should never take sildenafil at the same time as another PDE5 inhibitor such as tadalafil (Cialis), vardenafil (Levitra) or avanafil (Spedra) [3]. Taking two PDE5 inhibitors together can cause a dangerous drop in blood pressure and increase the risk of serious side effects. If one ED medicine is not working well for you, speak to your prescriber about trying a different one or adjusting the dose, but do not combine them.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 18 October 2026]
2. National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 18 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 18 October 2026]
4. Feldman, H. A., Goldstein, I., Hatzichristou, D. G., Krane, R. J., & McKinlay, J. B. (1994). Impotence and its medical and psychosocial correlates: Results of the Massachusetts Male Aging Study. Journal of Urology, 151(1), 54–61. https://pubmed.ncbi.nlm.nih.gov/8254833/ [accessed 18 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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