Tadalafil and Relugolix: Can You Take Them Together?

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Key takeaways

• No major direct interaction between tadalafil and relugolix is commonly reported.
• Relugolix lowers testosterone, which may reduce tadalafil effectiveness.
• Your prescriber reviews your full medical history and other medicines before approving tadalafil.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers.
• Speak to your doctor if ED persists; other treatments and support are available.

What is Tadalafil and How Does It Work?

Tadalafil is a prescription medicine used to treat erectile dysfunction 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][4]. Tadalafil is the active ingredient in branded Cialis and is also available as a generic medicine at lower cost.

Tadalafil is available in two main dosing options. The on-demand dose (usually 10mg or 20mg) is taken at least 30 minutes before sexual activity, and its effect can last up to 36 hours, earning it the nickname 'the weekend pill'. The daily dose (2.5mg or 5mg) is taken once every day at the same time, allowing for more spontaneous sexual activity [4]. Both options require sexual stimulation to work; tadalafil does not cause an automatic erection.

Common side effects include headache, indigestion, back pain, muscle aches, flushing, and a stuffy or runny nose [4]. Most side effects are mild and temporary. Tadalafil is only available on prescription in the UK after a healthcare professional has checked it is safe and suitable for you.

What is Relugolix and Why is It Prescribed?

Relugolix is a prescription medicine used to treat advanced hormone-sensitive prostate cancer in adult men. It is a type of hormone therapy known as a GnRH (gonadotropin-releasing hormone) receptor antagonist. Relugolix works by blocking the production of testosterone, a male hormone that can fuel the growth of prostate cancer cells.

By lowering testosterone levels in the body, relugolix helps to slow or stop the growth of prostate cancer. It is taken as a daily tablet, usually starting with a higher loading dose on the first day, followed by a lower daily maintenance dose. Relugolix is marketed under the brand name Orgovyx in some countries and is typically prescribed by a specialist oncologist or urologist.

Because relugolix significantly reduces testosterone, it can cause side effects related to low hormone levels, including hot flushes, tiredness, reduced sex drive, and erectile dysfunction. Many men on relugolix or similar hormone therapies experience ED as a result of the treatment itself, which is why questions about using tadalafil alongside relugolix are common and important.

At a glance

Can You Take Tadalafil and Relugolix Together?

There is no known major direct drug interaction between tadalafil and relugolix. This means that tadalafil does not interfere with how relugolix works to lower testosterone and control prostate cancer, and relugolix does not significantly affect how tadalafil is processed in the body. However, this does not automatically mean the combination is suitable for everyone.

Your prescriber will assess your individual situation carefully. Relugolix lowers testosterone, which can itself cause or worsen erectile dysfunction, so tadalafil may be less effective in some men on hormone therapy [1][2]. Your doctor will also check your cardiovascular health, blood pressure, and any other medicines you take, because tadalafil can interact with other drugs (such as nitrates, alpha-blockers, or certain antifungals and antibiotics) and is not suitable for men with certain heart conditions [3][4].

If you are taking relugolix for prostate cancer and experiencing ED, it is important to discuss this openly with your oncologist, urologist, or GP. They can review whether tadalafil or another ED treatment is appropriate, taking into account your cancer treatment, overall health, and any other medications. Never start tadalafil without a prescription and medical review, even if you have taken it before.

Why Your Prescriber Needs to Know About Relugolix

Even though tadalafil and relugolix do not directly interact, your prescriber must know about all your current medicines, including cancer treatments. Relugolix affects your hormone levels and overall health, which can influence whether ED treatment is safe and likely to work. Your prescriber will also check for other medicines you might be taking alongside relugolix (such as blood pressure tablets or medications for other conditions) that could interact with tadalafil. Full disclosure ensures you receive the safest, most effective treatment plan tailored to your needs.

What Your Prescriber Checks Before Approving Tadalafil

Before prescribing tadalafil, your doctor or pharmacist will ask about your medical history, current health, and all medicines you are taking, including relugolix and any over-the-counter products or supplements. They will check whether you have any conditions that make tadalafil unsuitable, such as recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or a history of sudden vision loss (NAION) [3][4].

Your prescriber will also review any other medicines that could interact with tadalafil. For example, tadalafil must never be taken with 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 take alpha-blockers for an enlarged prostate or high blood pressure, your prescriber will ensure you are stable on that medicine and may start you on a lower dose of tadalafil.

Certain medicines that affect liver enzymes (such as ritonavir, ketoconazole, itraconazole, or clarithromycin) can raise tadalafil levels in the body, requiring dose adjustments [4]. Your prescriber will also consider whether sexual activity is safe for you, especially if you have heart disease. At Cured Pharmacy, every prescription request is reviewed by a UK-registered prescriber to ensure tadalafil is safe and appropriate for you.

Practical Advice for Using Tadalafil with Relugolix

If your prescriber approves tadalafil while you are taking relugolix, follow the dosing instructions carefully. On-demand tadalafil (10mg or 20mg) should be taken at least 30 minutes before sexual activity, and you should not take more than one dose in 24 hours [4]. Daily tadalafil (2.5mg or 5mg) is taken once a day at the same time, regardless of when you plan to have sex. Remember that tadalafil requires sexual stimulation to work; it does not cause an erection on its own.

Be aware that relugolix lowers testosterone, which can reduce sex drive and make it harder to achieve or maintain an erection, even with tadalafil. Some men find that ED treatments are less effective during hormone therapy for prostate cancer [2]. Speak to your doctor if tadalafil does not help; they may adjust the dose, suggest a different ED medicine, or refer you to a specialist for other treatment options such as vacuum devices, injections, or psychological support.

Avoid drinking large amounts of alcohol, as it can worsen ED and increase the risk of side effects such as dizziness or low blood pressure when taking tadalafil [3][4]. Grapefruit juice can raise tadalafil levels in the blood, so it is best to avoid it. If you experience side effects such as severe headache, chest pain during sex, or an erection lasting more than four hours, seek medical help immediately. Always tell any doctor, dentist, or pharmacist that you are taking both relugolix and tadalafil.

Managing Expectations During Hormone Therapy

It is important to have realistic expectations when using tadalafil during hormone therapy for prostate cancer. Because relugolix suppresses testosterone, your sex drive and erectile function may be significantly affected, and ED medication may not work as well as it would in men with normal testosterone levels [1][2]. Open communication with your partner and healthcare team is key. Some men benefit from combining medical treatment with counselling or psychosexual therapy. Your wellbeing and quality of life matter, so do not hesitate to ask for support.

Other ED Treatments and Alternatives

If tadalafil is not suitable or effective for you while taking relugolix, other options may be available. Alternative PDE5 inhibitors include sildenafil (generic Viagra), vardenafil (generic Levitra), and avanafil (Spedra) [3][5][6]. Each works in a similar way but has different onset times and durations of action. Your prescriber can help you choose the best option based on your lifestyle and medical history.

For men who do not respond to tablets, other treatments include vacuum erection devices, which use suction to draw blood into the penis, or prescription medicines such as alprostadil, which can be applied as a cream (Vitaros) or given as an injection (Caverject) directly into the penis [7]. These options may be more effective in men with very low testosterone, though they require training and careful use.

Psychological factors such as anxiety, depression, or relationship stress can also contribute to ED, especially during cancer treatment. Counselling, cognitive behavioural therapy (CBT), or psychosexual therapy can be helpful, either alone or alongside medical treatment [2]. Your GP or specialist can refer you to appropriate services. At Cured Pharmacy, our online consultation allows you to discuss your needs confidentially with a UK prescriber, who can recommend the most suitable treatment or refer you for further support if needed.

When to See Your GP or Specialist

If you are experiencing new or worsening erectile dysfunction while taking relugolix, speak to your GP, oncologist, or urologist. ED can sometimes be an early sign of other health problems, such as heart disease or diabetes, so it is important to have it checked, even if you think it is caused by your cancer treatment [1][2]. Your doctor can also review whether any other medicines you are taking might be contributing to the problem and discuss the full range of treatment options available to you.

When to get urgent help

• Erection lasting more than 4 hours (priapism) – call 999 or go to A&E immediately
• Sudden loss of vision or hearing – seek urgent medical attention
• Chest pain during or after sex – stop activity and call 999
• Severe dizziness, fainting, or very low blood pressure – seek same-day medical help

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