Tadalafil and Propylthiouracil: Can You Take Them Together?

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Tadalafil and Propylthiouracil: Understanding the Interaction

Published: 24 October 2026

Many men taking propylthiouracil for an overactive thyroid wonder whether tadalafil and propylthiouracil can be taken together safely. The good news is that no major direct interaction between these two medicines is commonly reported in clinical practice [2][4]. However, every medication you take—including thyroid treatments—must be declared during your consultation, so your prescriber can check your full medical history and ensure tadalafil is suitable for you.

What is tadalafil and how does it work?

Tadalafil is a prescription medicine used to treat erectile dysfunction (ED) in men [1][4]. 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. Tadalafil is the active ingredient in Cialis and is available in both branded and generic forms.

Tadalafil can be taken in two ways: on-demand (10 mg or 20 mg at least 30 minutes before sexual activity, with effects lasting up to 36 hours) or as a daily low dose (2.5 mg or 5 mg) [4]. Unlike some other ED treatments, tadalafil's long duration of action means you don't need to time it as precisely, offering more spontaneity. It only works when you are sexually stimulated—it will not cause an erection on its own.

Common side effects include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. These are usually mild and temporary. Tadalafil is not suitable for everyone, particularly men taking nitrates, nicorandil, riociguat, or those with certain heart conditions, so a full medical assessment is essential before starting treatment.

What is propylthiouracil and why is it prescribed?

Propylthiouracil (often abbreviated as PTU) is a prescription medicine used to treat hyperthyroidism—a condition where the thyroid gland produces too much thyroid hormone [12]. It works by reducing the amount of thyroid hormone your body makes, helping to control symptoms such as a rapid heartbeat, weight loss, tremor, sweating, and anxiety.

Propylthiouracil is particularly used in certain situations, such as during the first trimester of pregnancy, in patients who cannot tolerate carbimazole (another anti-thyroid drug), or in thyroid storm (a severe, life-threatening form of hyperthyroidism) [12]. It is usually taken two or three times a day, and regular blood tests are needed to monitor thyroid function and check for rare but serious side effects, including liver problems and low white blood cell counts.

Because hyperthyroidism itself can affect many body systems—including the heart and circulation—it is important that your thyroid condition is well controlled. Untreated or poorly managed hyperthyroidism can contribute to cardiovascular problems, which may in turn affect erectile function. Your GP or endocrinologist will monitor your thyroid levels closely while you are on propylthiouracil.

Do tadalafil and propylthiouracil interact with each other?

There is no well-documented direct pharmacological interaction between tadalafil and propylthiouracil [2][4]. These medicines work on completely different systems in the body: tadalafil acts on blood vessels in the penis to improve erectile function, while propylthiouracil reduces thyroid hormone production. They are not known to interfere with each other's effectiveness or to increase the risk of side effects when taken together.

However, this does not mean you can simply start tadalafil without medical oversight. Every medicine you take—including propylthiouracil and any other treatments for your thyroid or other conditions—must be declared when you request ED treatment. Your prescriber will review your full medication list, medical history, and current health status to ensure tadalafil is safe and appropriate for you [2].

It is also worth noting that thyroid disorders themselves can sometimes contribute to erectile dysfunction. Hyperthyroidism can cause anxiety, fatigue, and cardiovascular changes that may affect sexual function, while hypothyroidism (underactive thyroid) is also linked to ED. Ensuring your thyroid condition is well managed with propylthiouracil or other treatments may help improve your overall wellbeing and sexual health.

Why your prescriber needs to know about all your medicines

Even when two medicines do not interact directly, your prescriber needs a complete picture of your health. Propylthiouracil is used to treat a condition that affects your heart, metabolism, and circulation—all factors that are relevant when assessing whether tadalafil is safe for you [2]. Your prescriber will also check for any other medicines you take that could interact with tadalafil, such as nitrates, alpha-blockers, or drugs that affect how tadalafil is broken down in the body.

Never stop or change your propylthiouracil or any other prescribed medicine without speaking to your doctor. If you have concerns about how your medicines work together, raise them during your consultation or contact your GP or pharmacist for advice.

What does your prescriber check before approving tadalafil?

When you request tadalafil through an online consultation at Cured Pharmacy, a UK-registered prescriber will review your answers to ensure the treatment is safe and suitable for you [2]. You will be asked about all current medicines (including propylthiouracil), medical conditions (especially heart, liver, and kidney problems), blood pressure, and any history of stroke, heart attack, or eye disorders.

The prescriber will specifically check for contraindications—medicines or conditions that mean tadalafil must not be used. These include nitrates (such as GTN spray or isosorbide mononitrate), nicorandil, riociguat, and recreational drugs known as 'poppers' (amyl or alkyl nitrites) [3][4]. Taking tadalafil with any of these can cause a dangerous drop in blood pressure. You must also not take tadalafil alongside another PDE5 inhibitor (such as sildenafil or vardenafil).

If you take medicines that lower blood pressure (including some used for an enlarged prostate, such as alpha-blockers), or drugs that affect how tadalafil is processed in the liver (such as certain antibiotics, antifungals, or HIV medicines), your prescriber may adjust the dose or recommend an alternative [4]. This careful review is why it is essential to list every medicine, supplement, and over-the-counter product you use, no matter how minor it seems.

Declaring your thyroid condition and treatment

Your thyroid condition and propylthiouracil treatment should be declared in your consultation. While propylthiouracil itself does not stop you from using tadalafil, your prescriber needs to know that you have hyperthyroidism, as this can affect your heart and circulation [2]. If your thyroid is not well controlled, or if you have developed heart rhythm problems or other complications, your prescriber may want you to discuss ED treatment with your GP first.

Being open and thorough in your consultation helps ensure you receive safe, effective treatment tailored to your individual circumstances.

Practical advice for taking tadalafil and propylthiouracil together

If your prescriber approves tadalafil, you can take it alongside propylthiouracil as directed. Take each medicine exactly as prescribed: propylthiouracil is usually taken two or three times daily with or without food, while tadalafil on-demand is taken at least 30 minutes before sexual activity (or daily tadalafil is taken once a day at the same time) [4][12]. There is no need to separate the doses or avoid taking them on the same day.

Keep all your regular appointments and blood tests for your thyroid condition. Good control of hyperthyroidism is important for your overall health and may also help improve erectile function if thyroid-related symptoms have been contributing to ED. If you notice any new symptoms—such as dizziness, chest pain, sudden vision or hearing loss, or an erection lasting more than four hours—seek medical help immediately.

Avoid drinking large amounts of alcohol when using tadalafil, as alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of the medicine, increasing the risk of dizziness or fainting [4]. Grapefruit juice can raise tadalafil levels in the blood, so it is best avoided. If you are prescribed a new medicine by your GP or specialist, always mention that you are taking tadalafil, and check with your pharmacist if you are unsure about any over-the-counter products.

When to seek further advice about tadalafil and propylthiouracil

If you experience side effects from either medicine, or if your erectile dysfunction does not improve with tadalafil, speak to your prescriber or GP. Common side effects of tadalafil (headache, indigestion, back pain, flushing) are usually mild, but if they are troublesome or persistent, a dose adjustment or alternative treatment may help [4]. Propylthiouracil can occasionally cause serious side effects, including liver problems and low white blood cell counts, so report any unexplained fever, sore throat, mouth ulcers, bruising, or yellowing of the skin to your doctor immediately [12].

Erectile dysfunction can be an early warning sign of underlying health problems, such as heart disease or diabetes [1][2]. If you have not already done so, see your GP for a full assessment, especially if ED is a new problem or if you have other symptoms such as chest pain, shortness of breath, or fatigue. Your GP can investigate potential causes, optimise management of your thyroid condition and any other health issues, and refer you to a specialist if needed.

Remember, you should never stop taking propylthiouracil or any other prescribed medicine without medical advice, even if you are concerned about interactions or side effects. Your pharmacist and prescriber are here to help you manage your medicines safely and answer any questions you may have about taking tadalafil and propylthiouracil together.

Getting ED treatment through Cured Pharmacy

Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering discreet, convenient access to ED treatments after a clinical consultation reviewed by a UK prescriber. You will complete a short online questionnaire about your health and current medicines, including propylthiouracil. If tadalafil is suitable, your prescription will be dispensed and delivered discreetly to your door.

We stock a range of ED treatments, including generic and branded tadalafil, sildenafil, vardenafil, and avanafil, so your prescriber can recommend the option that best fits your needs and lifestyle. All treatments require a prescription and are only supplied after a thorough clinical review to ensure your safety.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 24 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 24 October 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 24 October 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 24 October 2026]
5. Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 24 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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