Tadalafil and Bosentan: Can They Be Taken Together?

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Key takeaways

• Bosentan reduces tadalafil blood levels by about 40%, so your specialist may increase the tadalafil dose.
• Both medicines lower blood pressure; careful monitoring and dose adjustment are essential.
• Never take tadalafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor.
• Regular blood tests and specialist follow-up are required when taking both medicines together.
• Seek urgent help for chest pain, severe dizziness, sudden vision or hearing loss, or erection lasting over four hours.

What is tadalafil and what is it used for?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK for two main conditions: erectile dysfunction and pulmonary arterial hypertension [4]. For ED, tadalafil is available as on-demand tablets (usually 10 mg or 20 mg taken at least 30 minutes before sexual activity, with effects lasting up to 36 hours) or as a daily low-dose tablet (2.5 mg or 5 mg) [4]. It works by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused.

Tadalafil is also prescribed at a higher dose (usually 40 mg daily) for pulmonary arterial hypertension, a serious condition where blood pressure in the arteries of the lungs is abnormally high [4]. In PAH, tadalafil helps relax and widen the pulmonary arteries, reducing the strain on the heart. Whether used for ED or PAH, tadalafil lowers blood pressure to some degree, which is an important consideration when it is combined with other medicines.

What is bosentan and why is it prescribed?

Bosentan is an endothelin receptor antagonist used to treat pulmonary arterial hypertension. Endothelin is a natural substance that narrows blood vessels; bosentan blocks its action, allowing the pulmonary arteries to relax and widen. This reduces blood pressure in the lungs and helps the heart pump more efficiently. Bosentan is typically started in hospital under specialist supervision and requires regular blood tests to monitor liver function, as it can affect the liver.

Because bosentan is a potent inducer of certain liver enzymes (specifically CYP3A4 and CYP2C9), it speeds up the breakdown of many other medicines in the body. This means that drugs processed by these enzymes—including tadalafil—may be cleared from the bloodstream more quickly, potentially reducing their effectiveness. Understanding this interaction is essential for anyone taking both medicines.

At a glance

How do tadalafil and bosentan interact with each other?

When tadalafil and bosentan are taken together, bosentan reduces the blood levels of tadalafil by increasing how quickly the body breaks it down [4]. In clinical studies, bosentan decreased tadalafil exposure by approximately 40%, meaning tadalafil may be less effective at its usual dose. At the same time, tadalafil can slightly increase bosentan levels, though this effect is generally considered less clinically significant.

Both medicines also lower blood pressure, so taking them together can add to this effect, potentially causing dizziness, light-headedness, or fainting, especially when standing up quickly. This does not mean the combination is forbidden—many patients with pulmonary arterial hypertension are successfully treated with both—but it does require specialist oversight, careful dose adjustment, and monitoring of blood pressure and symptoms.

What happens in your body when you take both medicines?

Bosentan activates enzymes in your liver that break down tadalafil more rapidly than usual. As a result, tadalafil does not stay in your system as long, and its peak effect may be reduced. Your prescriber may need to increase the dose of tadalafil to achieve the desired therapeutic effect, or they may time the doses carefully to minimise the interaction. Meanwhile, the combined blood-pressure-lowering effect means your body has to work harder to maintain stable blood pressure, particularly when you change position or exert yourself. Your specialist will monitor you for signs of low blood pressure and adjust treatment as needed.

What will your prescriber check before combining tadalafil and bosentan?

If you are being considered for both tadalafil and bosentan, your prescriber (usually a cardiologist or respiratory specialist) will review your full medical history, current medicines, blood pressure, heart function, and liver function [2][4]. They will check whether you have any conditions that make either medicine unsuitable, such as severe liver disease, recent heart attack or stroke, or very low blood pressure. Blood tests will be arranged to assess your liver enzymes before starting bosentan and at regular intervals during treatment.

Your prescriber will also ask about any other medicines you take, including over-the-counter products and herbal supplements, because many drugs interact with tadalafil or bosentan. They will ensure you are not taking nitrates, nicorandil, riociguat, or another PDE5 inhibitor, as these combinations are dangerous [3][4]. If you are on other blood-pressure medicines or drugs that affect liver enzymes, doses may need adjusting. The consultation will include advice on recognising warning signs such as dizziness, fainting, or worsening breathlessness, and when to seek urgent help.

Practical advice for taking tadalafil and bosentan together

If your specialist has prescribed both medicines, take them exactly as directed and do not adjust doses yourself. Because bosentan reduces tadalafil levels, your doctor may prescribe a higher dose of tadalafil than would normally be used, or they may recommend taking tadalafil at a different time of day to optimise its effect. Keep all follow-up appointments and blood tests, as regular monitoring is essential to ensure both medicines are working safely.

Stand up slowly from sitting or lying down to reduce the risk of dizziness or fainting. Avoid heavy alcohol, as it can worsen low blood pressure and erectile dysfunction. Do not take grapefruit juice with tadalafil, as it can unpredictably raise tadalafil levels. If you develop new symptoms—such as severe dizziness, chest pain, sudden vision or hearing loss, or an erection lasting more than four hours—seek medical help immediately. Never stop or change either medicine without consulting your specialist, as both are treating serious underlying conditions.

What if you are taking tadalafil for erectile dysfunction and start bosentan?

If you are already taking tadalafil for ED and your doctor prescribes bosentan for pulmonary arterial hypertension, inform both your GP and your specialist. The bosentan will reduce the effectiveness of your ED treatment, so your prescriber may need to increase the tadalafil dose or consider an alternative approach. Do not simply take more tadalafil on your own, as this can be unsafe. Your care team will coordinate your treatment to ensure both conditions are managed effectively and safely.

Warning signs and when to seek urgent help with tadalafil and bosentan

While many people tolerate the combination of tadalafil and bosentan well under specialist care, certain symptoms require immediate medical attention. Seek emergency help (call 999 or go to A&E) if you experience chest pain during sexual activity, sudden severe dizziness or fainting, sudden loss of vision or hearing, or an erection that lasts more than four hours (priapism). These are rare but serious side effects that need urgent treatment.

Contact your specialist or GP the same day if you develop new or worsening breathlessness, swelling of the ankles or legs, yellowing of the skin or eyes (jaundice), dark urine, or persistent nausea and vomiting, as these may indicate liver problems or worsening heart function. Regular monitoring and open communication with your healthcare team are key to using both medicines safely and effectively. Never hesitate to ask questions or report new symptoms—your prescriber is there to support you.

Can you take other erectile dysfunction medicines with bosentan?

All PDE5 inhibitors—sildenafil, vardenafil, and avanafil—are affected by bosentan in a similar way to tadalafil, as they are all broken down by the same liver enzymes [3][5][6]. If bosentan is part of your treatment, your prescriber will choose the most appropriate ED medicine and dose for your situation, taking the interaction into account. You must never take more than one PDE5 inhibitor at a time, and you must not take any PDE5 inhibitor with nitrates, nicorandil, riociguat, or poppers, as these combinations can cause a dangerous drop in blood pressure. Always declare all your medicines during any consultation for ED treatment.

When to get urgent help

• Chest pain during or after sexual activity
• Sudden severe dizziness, fainting, or collapse
• Sudden loss of vision or hearing
• Erection lasting more than four hours (priapism)
• Yellowing of skin or eyes, dark urine, or severe nausea (possible liver problem)

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

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