Tadalafil and Carbimazole: Can You Take Them Together?
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Tadalafil and Carbimazole: Understanding the Interaction
Published: 19 October 2026
Many men wonder whether tadalafil and carbimazole can be taken together safely. The good news is that no major interaction is commonly reported between tadalafil (a medicine for erectile dysfunction) and carbimazole (used to treat an overactive thyroid). However, your prescriber will still review your full medical history and current medicines during your consultation to ensure tadalafil is suitable for you, as thyroid disorders can sometimes affect cardiovascular health.
Always Declare All Your Medicines
During your online consultation, list every medicine you take, including carbimazole, over-the-counter products, and supplements. This ensures your prescriber can check for interactions and prescribe tadalafil safely.
What Is Tadalafil and How Does It Work?
Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men. It belongs to a group of medicines called PDE5 inhibitors, which work by relaxing blood vessels in the penis, allowing increased blood flow when you are sexually aroused [3][4]. Tadalafil is the generic name for Cialis and is available in two forms: on-demand tablets (10mg or 20mg taken at least 30 minutes before sex, with effects lasting up to 36 hours) and daily low-dose tablets (2.5mg or 5mg taken every day) [4].
Unlike some ED medicines, tadalafil has a longer duration of action, which is why it is sometimes called 'the weekend pill'. It does not cause an erection on its own—sexual stimulation is still needed for it to work [4]. Tadalafil is only available on prescription in the UK after a clinical assessment by a registered prescriber, who will check your medical history, current medicines, and cardiovascular health to ensure it is safe for you.
What Is Carbimazole and Why Is It Prescribed?
Carbimazole is a prescription medicine used to treat hyperthyroidism (an overactive thyroid gland). The thyroid produces hormones that regulate your metabolism, heart rate, and body temperature. When the thyroid is overactive, it produces too much thyroid hormone, leading to symptoms such as a rapid heartbeat, weight loss, sweating, anxiety, and tremors. Carbimazole works by reducing the amount of thyroid hormone your body produces, helping to bring hormone levels back to normal.
Treatment with carbimazole is usually started by a specialist or GP and requires regular blood tests to monitor thyroid function and adjust the dose. It can take several weeks for carbimazole to bring thyroid hormone levels under control. Some people take carbimazole for a few months to a couple of years, while others may need longer-term treatment depending on the underlying cause of their hyperthyroidism. It is important not to stop or change your carbimazole dose without medical advice, as this can cause your thyroid levels to become unbalanced again.
When to get urgent help
- Erection lasting more than 4 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 or dizziness – seek medical help
- Chest pain during or after sex – stop activity and seek urgent advice; do not take nitrates if you've used tadalafil in the last 48 hours
- Severe dizziness, fainting, or very fast/irregular heartbeat – contact your GP or call 111
Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.
Do Tadalafil and Carbimazole Interact With Each Other?
There is no commonly reported direct interaction between tadalafil and carbimazole. These two medicines work on different systems in the body: tadalafil affects blood flow to the penis, while carbimazole reduces thyroid hormone production. They are not known to interfere with each other's effectiveness or increase the risk of side effects when taken together.
However, it is important to understand that hyperthyroidism itself can affect your cardiovascular system. An overactive thyroid can cause a rapid or irregular heartbeat (atrial fibrillation), high blood pressure, and increased strain on the heart. Because tadalafil is a medicine that affects blood vessels and blood pressure, your prescriber will want to ensure your thyroid condition is well-controlled and that your heart is healthy enough for sexual activity before prescribing tadalafil [1][2]. This is why you must declare all your current medicines and medical conditions during your online consultation.
Why Your Prescriber Checks Your Thyroid Health
During your consultation, the prescriber will ask about your thyroid condition, how well it is controlled, and whether you have any heart-related symptoms such as palpitations or chest discomfort. If your hyperthyroidism is untreated or poorly controlled, it may not be safe to use tadalafil until your thyroid levels are stable. Your prescriber may also check whether you are taking any other medicines that could interact with tadalafil, such as nitrates, alpha-blockers, or medicines that affect how tadalafil is broken down in the body [3][4].
What Your Prescriber Will Check Before Prescribing Tadalafil
Before tadalafil can be prescribed, a UK-registered prescriber will review your full medical history and current medicines. They will ask about your cardiovascular health, including blood pressure, any history of heart attack, stroke, or angina, and whether you have any conditions that make sexual activity inadvisable [2]. If you have hyperthyroidism, the prescriber will want to know whether it is being treated, how well controlled it is, and whether you have experienced any heart-related complications.
You will also be asked about all the medicines you are currently taking, including prescription medicines, over-the-counter products, and herbal supplements. This is because tadalafil must not be taken with certain medicines, including nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, or recreational drugs known as 'poppers' (amyl or alkyl nitrites), as the combination can cause a dangerous drop in blood pressure [3][4]. If you take alpha-blockers for prostate symptoms or high blood pressure, the prescriber will ensure you are stable on that medicine and may start you on a lower dose of tadalafil.
Medicines That Affect Tadalafil Levels
Some medicines can increase or decrease the levels of tadalafil in your blood. Potent CYP3A4 inhibitors, such as ritonavir, cobicistat, ketoconazole, itraconazole, and clarithromycin, can raise tadalafil levels, meaning a lower maximum dose may be needed [4]. Conversely, CYP3A4 inducers like rifampicin, carbamazepine, phenytoin, and St John's wort can reduce tadalafil levels and make it less effective. Your prescriber will check for these interactions and adjust your treatment plan accordingly.
At a glance
Practical Advice for Taking Tadalafil With Carbimazole
If your prescriber confirms that tadalafil is suitable for you, you can take it alongside carbimazole without concern about a direct interaction. Take each medicine exactly as prescribed: carbimazole is usually taken once or twice a day at the same time each day, while tadalafil on-demand tablets are taken at least 30 minutes before sexual activity (or daily tablets are taken at the same time every day) [4]. Do not take more than one dose of on-demand tadalafil in 24 hours.
Continue to attend your regular thyroid monitoring appointments and blood tests as advised by your GP or specialist. If your thyroid treatment changes or if you develop new symptoms such as chest pain, palpitations, dizziness, or shortness of breath, contact your GP promptly. Avoid drinking large amounts of alcohol when using tadalafil, as this can increase the risk of dizziness and low blood pressure, and may worsen erectile dysfunction [1]. Grapefruit juice can also raise tadalafil levels, so it is best to avoid it.
When to Seek Medical Help and Warning Signs
Most men tolerate tadalafil well, but you should be aware of warning signs that require urgent medical attention. If you experience an erection lasting more than four hours (priapism), seek emergency help immediately, as this can cause permanent damage if not treated promptly [3][4]. Sudden loss of vision in one or both eyes or sudden decrease or loss of hearing (sometimes with ringing in the ears or dizziness) are rare but serious side effects that require you to stop taking tadalafil and seek medical help straight away.
If you develop chest pain during or after sexual activity, stop and seek urgent medical advice. Do not take nitrates (such as GTN spray) to relieve chest pain if you have taken tadalafil within the last 48 hours, as this combination can cause a dangerous drop in blood pressure [3][4]. If you notice any new or worsening symptoms related to your thyroid condition, such as a very fast or irregular heartbeat, severe sweating, or unexplained weight loss, contact your GP or specialist for review. Always read the patient information leaflet that comes with your medicine and report any side effects to your prescriber or pharmacist.
Reporting Side Effects
If you experience side effects from tadalafil or carbimazole, you can report them via the Yellow Card Scheme at yellowcard.mhra.gov.uk or by searching for 'Yellow Card' in the Google Play or Apple App Store. Common side effects of tadalafil include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. These are usually mild and temporary. If side effects are troublesome or persistent, speak to your prescriber, who may adjust your dose or suggest an alternative ED treatment.
In summary
- No major interaction is commonly reported between tadalafil and carbimazole
- Your prescriber checks thyroid control and heart health before prescribing tadalafil
- Hyperthyroidism can affect cardiovascular health, so stable thyroid levels are important
- Never take tadalafil with nitrates, nicorandil, riociguat, or poppers
- Seek urgent help for erections lasting over 4 hours or sudden vision or hearing loss
Scientific References
- NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 19 October 2026]
- National Institute for Health and Care Excellence. (n.d.). Erectile dysfunction. Clinical Knowledge Summaries. https://cks.nice.org.uk/topics/erectile-dysfunction/ [accessed 19 October 2026]
- Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 19 October 2026]
- Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 19 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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Medically reviewed by
Tarun Kumar, Superintendent Pharmacist (GPhC 2233073)