Tadalafil and Quinine: Can They Be Taken Together?

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Key takeaways

• No major interaction between tadalafil and quinine is commonly reported in clinical practice.
• Your prescriber will review your heart health and all current medicines during your consultation.
• Never take tadalafil with nitrates, nicorandil, riociguat, or poppers—this can be dangerous.
• Declare all medicines, including over-the-counter products, to ensure tadalafil is safe for you.
• Seek urgent help for chest pain during sex, erection lasting over 4 hours, or sudden vision loss.

What is tadalafil and how does it work?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK to treat erectile dysfunction (ED). It works by relaxing the blood vessels in the penis, allowing increased blood flow when you are sexually aroused [4]. Unlike some other ED treatments, tadalafil can remain effective for up to 36 hours after taking a dose, which is why it's sometimes called the 'weekend pill'.

Tadalafil is available in two ways: on-demand tablets (10mg or 20mg taken at least 30 minutes before sexual activity) or daily low-dose tablets (2.5mg or 5mg taken once a day) [4]. Both require sexual stimulation to work—tadalafil does not cause an automatic erection. It's important to note that tadalafil can lower blood pressure slightly, which is relevant when considering interactions with other medicines.

Common brand names include Cialis (the original branded version) and various generic versions. All prescription ED medicines in the UK are only supplied after an online or face-to-face consultation reviewed by a UK-registered prescriber, who will check your medical history and current medicines.

What is quinine and why is it prescribed?

Quinine is a medicine most commonly prescribed in the UK for nocturnal leg cramps—painful muscle spasms that occur at night. It's typically given as quinine sulfate tablets, usually 200mg or 300mg taken at bedtime. Quinine works by reducing the excitability of the motor end-plate, which helps prevent the involuntary muscle contractions that cause cramps.

Historically, quinine was also used to treat malaria, though newer antimalarial medicines are now preferred for that purpose. In the UK, quinine for leg cramps is prescription-only and is usually considered only after other measures (such as stretching exercises and ensuring good hydration) have been tried.

Quinine can have side effects including nausea, headache, ringing in the ears (tinnitus), and visual disturbances. More seriously, it can affect heart rhythm in some people, particularly at higher doses or in those with existing heart conditions. Your prescriber will review your full medical history before prescribing quinine, and regular monitoring may be recommended if you take it long-term.

At a glance

Do tadalafil and quinine interact with each other?

No major interaction between tadalafil and quinine is commonly reported in standard drug interaction databases or clinical practice. This means that for most men, taking these two medicines together does not usually cause significant problems. However, both medicines can have effects on the cardiovascular system, so your prescriber will still want to review the combination carefully during your consultation.

Tadalafil can cause a small drop in blood pressure, and quinine has been associated with heart rhythm changes (QT prolongation) in some cases. While these effects are usually mild when each medicine is taken alone, your prescriber will consider your overall heart health, other medicines you take, and any existing conditions before confirming that the combination is suitable for you.

It's essential to declare all your current medicines—including over-the-counter products, herbal remedies, and supplements—during your ED consultation. The prescriber will check for any potential interactions and ensure that tadalafil is safe and appropriate for you. Never stop taking a medicine prescribed by your GP (such as quinine) without discussing it with them first.

What your prescriber will check

During your consultation for tadalafil, the prescriber will ask about your current medicines, including quinine. They will review your cardiovascular health, blood pressure, and any history of heart rhythm problems. If you have certain heart conditions or take medicines that significantly affect heart rhythm, additional caution may be needed. The prescriber may recommend starting on a lower dose of tadalafil or suggest monitoring for any unusual symptoms such as dizziness, palpitations, or chest discomfort.

Other medicines that interact with tadalafil

While tadalafil and quinine can usually be taken together, there are some medicines that must never be combined with tadalafil because they can cause a dangerous drop in blood pressure. These include nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, and amyl or alkyl nitrites (poppers). Do not take tadalafil with any of these medicines [4].

Alpha-blockers (such as doxazosin, tamsulosin, or alfuzosin) are used for prostate problems or high blood pressure and can also lower blood pressure. If you take an alpha-blocker, you should be stable on it before starting tadalafil, and your prescriber will usually recommend the lowest dose of tadalafil to start [4]. Potent CYP3A4 inhibitors (such as ritonavir, cobicistat, ketoconazole, itraconazole, or clarithromycin) can raise tadalafil levels in your blood, so your prescriber may reduce the maximum dose of tadalafil [4].

Other blood-pressure medicines can add to the blood-pressure-lowering effect of tadalafil, potentially causing dizziness. This is usually manageable, but it must be declared during your consultation. Grapefruit juice can also raise tadalafil levels, so it's best to avoid it. Heavy alcohol can worsen erectile dysfunction and add to the risk of low blood pressure.

Practical advice for taking tadalafil and quinine together

If your prescriber confirms that tadalafil is suitable for you and you are already taking quinine, there are some practical steps to help you use both medicines safely. Take each medicine exactly as prescribed—quinine is usually taken once daily at bedtime for leg cramps, while tadalafil can be taken on-demand (at least 30 minutes before sexual activity) or as a daily low dose.

Be aware of how you feel when you first start tadalafil, especially if you are taking other medicines that can affect blood pressure or heart rhythm. Common side effects of tadalafil include headache, indigestion, back pain, and flushing, which are usually mild [4]. If you experience dizziness, palpitations, or feel faint, sit or lie down and contact your GP or pharmacist for advice.

Keep a list of all your medicines (including doses and how often you take them) and share it with every healthcare professional you see. If you develop new symptoms or are prescribed a new medicine by your GP or a specialist, let them know you are taking tadalafil. Do not buy ED medicines from unregulated websites, as they may be counterfeit or unsafe.

When to seek medical advice

Seek urgent medical help (call 999 or go to A&E) if you experience chest pain during or after sex, an erection lasting more than four hours (priapism), or sudden loss of vision or hearing. Contact your GP or pharmacist promptly if you notice unusual dizziness, fainting, palpitations, or any other concerning symptoms after starting tadalafil. If you are unsure whether a symptom is related to your medicines, it is always better to ask.

Getting tadalafil safely from Cured Pharmacy

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering a range of ED treatments after a clinical consultation reviewed by a UK-registered prescriber. All prescription medicines, including tadalafil, require an online assessment where you will be asked about your medical history, current medicines (including quinine), and any other relevant health information [1][2].

We offer both generic and branded tadalafil options. Generic tadalafil is available from £7.95 (or £6.36 for your first order with code Ednew), while branded Cialis is available from £12.00 (or £9.60 with code Ednew). Tadalafil 20mg (Teva) is priced at £9.99 (or £7.99 with code Ednew), and Avarante (tadalafil) 10mg is £11.49 (or £9.19 with code Ednew). All products are dispensed by our UK pharmacists and delivered discreetly to your door.

If you are new to ED treatment or have not seen your GP recently, we encourage you to book a face-to-face appointment. Erectile dysfunction can be an early warning sign of heart disease or diabetes, so it's important to have a full health check [1]. Our prescribers will review your consultation carefully and may recommend that you see your GP for further tests before starting treatment.

Other ED treatment options

If tadalafil is not suitable for you, other PDE5 inhibitors are available, including sildenafil (generic Viagra, from £0.45 or £0.36 with code Ednew), vardenafil (generic Levitra, £16.95 or £13.56 with code Ednew), and avanafil (Spedra, £20.95 or £16.76 with code Ednew) [3][5][6]. Each has a slightly different onset and duration of action, and your prescriber can help you choose the most suitable option based on your lifestyle and preferences.

When to get urgent help

• Chest pain during or after sexual activity—call 999 immediately
• Erection lasting more than 4 hours (priapism)—go to A&E
• Sudden loss of vision or hearing—seek urgent medical attention
• Severe dizziness, fainting, or palpitations—contact your GP or call 111
• Allergic reaction (swelling of face, lips, tongue, or difficulty breathing)—call 999

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

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