Tadalafil and Levothyroxine: Can You Take Them Together?
Learn about interactions, safety, and what your prescriber checks during your UK consultation.
Takes less than 2 minutes to complete 100% online
Tadalafil and Levothyroxine: Understanding the Interaction
Published: 22 October 2026
Many men taking levothyroxine for an underactive thyroid wonder whether tadalafil and levothyroxine can be taken together safely. The good news is that no major direct interaction between tadalafil (Cialis) and levothyroxine is commonly reported, and many men use both medicines without problems. However, your prescriber will still check your full medical history and current medicines during your consultation to ensure tadalafil is suitable for you.
At a glance
What is tadalafil and levothyroxine used for?
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 active ingredient in Cialis and is available in on-demand doses (10mg or 20mg, taken at least 30 minutes before sex, with effects lasting up to 36 hours) or as a daily low dose (2.5mg or 5mg) [4].
Levothyroxine is a thyroid hormone replacement used to treat hypothyroidism (an underactive thyroid gland). It replaces or provides more thyroid hormone, which is normally produced by the thyroid gland. Levothyroxine is usually taken once daily, typically in the morning on an empty stomach, and is a long-term treatment for most people [12]. Hypothyroidism itself can contribute to erectile dysfunction, so treating your thyroid condition properly may help improve ED symptoms over time [1].
Is there an interaction between tadalafil and levothyroxine?
No significant direct interaction between tadalafil and levothyroxine is commonly reported in the British National Formulary or major drug interaction databases [3][4][12]. This means that the two medicines do not usually affect how each other works in your body, and many men take both safely together. Levothyroxine does not interfere with the way tadalafil relaxes blood vessels, and tadalafil does not affect thyroid hormone levels or how levothyroxine is absorbed.
However, it is important to understand that untreated or poorly controlled hypothyroidism can itself contribute to erectile dysfunction [1]. If your thyroid levels are not well managed, you may find that ED treatments are less effective. Your prescriber will want to know about your thyroid condition and whether your levothyroxine dose is stable and your thyroid function is well controlled. This helps them assess whether tadalafil is likely to work well for you and whether any adjustments to your overall treatment plan might be helpful.
Why your prescriber still needs to know
Even though tadalafil and levothyroxine do not interact directly, your prescriber must review all your current medicines and health conditions during your consultation. This is because tadalafil can interact with other medicines you might be taking, and certain health conditions can make tadalafil unsuitable or require a dose adjustment [3][4]. For example, if you also take medicines for high blood pressure, heart conditions, or certain antibiotics or antifungals, these may interact with tadalafil. Always declare every medicine you take, including over-the-counter products and supplements, so your prescriber can check for any potential issues.
What does your prescriber check before prescribing tadalafil?
When you request tadalafil through an online consultation at Cured Pharmacy, a UK-registered prescriber will review your medical history and current medicines to ensure it is safe for you [2]. They will check for conditions that make tadalafil unsuitable, such as recent heart attack or stroke, unstable angina, severe heart failure, very low blood pressure, or previous sudden vision loss (NAION) [3][4]. They will also check whether you take any medicines that interact dangerously with tadalafil, such as nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or poppers (amyl or alkyl nitrites). If you take any of these, you must not take tadalafil, as the combination can cause a dangerous drop in blood pressure [3][4].
Your prescriber will also ask about medicines that can raise tadalafil levels in your blood, such as potent CYP3A4 inhibitors (for example, ritonavir, cobicistat, ketoconazole, itraconazole, or clarithromycin). If you take any of these, your tadalafil dose may need to be reduced [4]. Alpha-blockers (such as tamsulosin or doxazosin, used for prostate problems or high blood pressure) can add to the blood-pressure-lowering effect of tadalafil, so you should be stable on the alpha-blocker and start on the lowest tadalafil dose [3][4]. Your prescriber will also want to know about your thyroid condition and whether your levothyroxine dose is stable, as well-controlled thyroid function is important for overall health and may influence how well ED treatment works for you.
What you need to know
- No major interaction between tadalafil and levothyroxine is commonly reported; many men take both safely.
- Hypothyroidism can contribute to ED; treating it with levothyroxine may help improve erectile function.
- Always declare all medicines during your consultation so your prescriber can check for other interactions.
- Never take tadalafil with nitrates, nicorandil, riociguat, or poppers due to dangerous blood pressure drops.
- Well-controlled thyroid levels are important for overall health and may help ED treatment work better.
Practical advice for taking tadalafil and levothyroxine together
If your prescriber approves tadalafil for you, you can take it alongside your levothyroxine without any special timing or precautions related to the interaction between the two medicines. However, it is good practice to take levothyroxine as directed—usually once daily in the morning, at least 30 minutes before breakfast, and at least 4 hours apart from other medicines that can interfere with its absorption (such as calcium, iron, or antacids) [12]. Tadalafil can be taken with or without food, though a very heavy or high-fat meal may delay how quickly it works [4].
For on-demand tadalafil (10mg or 20mg), take it at least 30 minutes before you plan to have sex; the effect can last up to 36 hours, so you do not need to time it precisely [4]. For daily tadalafil (2.5mg or 5mg), take it at the same time each day, and you will be ready for sexual activity at any time [4]. Remember that all PDE5 inhibitors, including tadalafil, require sexual stimulation to work—they do not cause an automatic erection [3][4]. Avoid heavy alcohol, as it can worsen ED and add to the blood-pressure-lowering effect of tadalafil. Do not take tadalafil with grapefruit juice, as this can raise tadalafil levels in your blood [4].
Monitoring your thyroid and ED treatment
Keep taking your levothyroxine exactly as prescribed and attend regular blood tests to monitor your thyroid function, as advised by your GP. Well-controlled thyroid levels are important for your overall health and may help improve erectile function over time [1]. If you notice that tadalafil is not working as well as expected, or if you experience new symptoms such as fatigue, weight changes, or mood changes, speak to your GP, as your levothyroxine dose may need adjusting. Do not stop or change the dose of any prescribed medicine without advice from your doctor or pharmacist.
Can levothyroxine and thyroid problems affect erectile dysfunction?
Yes, hypothyroidism (an underactive thyroid) is a recognised cause of erectile dysfunction [1]. Thyroid hormones play a role in regulating metabolism, energy levels, and blood flow, and low thyroid hormone levels can reduce libido (sex drive) and make it harder to get or keep an erection. Other symptoms of hypothyroidism include tiredness, weight gain, feeling cold, and low mood, all of which can also affect sexual function [12].
Treating hypothyroidism with levothyroxine can improve these symptoms, including erectile function, once your thyroid hormone levels are stable [1]. However, it may take several weeks or months for levothyroxine to bring your thyroid levels back to normal, and some men may still experience ED even after their thyroid is well controlled. In these cases, a PDE5 inhibitor such as tadalafil can help by directly improving blood flow to the penis [3][4]. If you have been diagnosed with hypothyroidism and are experiencing ED, it is important to have your thyroid function checked regularly and to discuss ED treatment options with your GP or through an online consultation with a UK prescriber.
When to get urgent help
- Erection lasting more than 4 hours (priapism) – go to A&E immediately
- Sudden loss of vision or hearing – seek urgent medical help
- Chest pain during sex after taking tadalafil – call 999; do not take nitrates (GTN spray)
- Severe dizziness, fainting, or very low blood pressure – seek same-day medical advice
- New symptoms suggesting thyroid problems (severe fatigue, rapid weight change, chest pain) – contact your GP urgently
Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.
When to seek medical advice about tadalafil and levothyroxine
If you experience any side effects from tadalafil, such as headache, indigestion, back pain, muscle aches, flushing, or nasal congestion, these are usually mild and temporary [3][4]. However, you should seek urgent medical help if you have an erection lasting more than 4 hours (priapism), sudden loss of vision or hearing, or chest pain during sex [3][4]. If chest pain occurs during sex, do not take nitrate medicines (such as GTN spray) to relieve it if you have taken tadalafil in the last 48 hours, as this combination is dangerous. Call 999 or go to A&E immediately and tell the healthcare team that you have taken tadalafil [3][4].
If you notice symptoms that might suggest your thyroid is not well controlled—such as increasing tiredness, weight changes, feeling unusually cold or hot, or mood changes—speak to your GP, as your levothyroxine dose may need adjusting [12]. If you start any new medicine, including over-the-counter or herbal products, check with your pharmacist or GP whether it is safe to take with tadalafil and levothyroxine. Never stop taking levothyroxine or tadalafil without advice from a healthcare professional.
How Cured Pharmacy can help
Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering a discreet, convenient service for erectile dysfunction treatment. After you complete an online consultation, a UK-registered prescriber will review your answers, including your current medicines such as levothyroxine, and approve tadalafil if it is safe and suitable for you. Your medicine is then dispensed by our pharmacy team and delivered discreetly to your door. If you have any questions about taking tadalafil with levothyroxine or any other medicine, our pharmacists are here to help—just contact us through the website.
Keep your thyroid well controlled
Taking levothyroxine as prescribed and attending regular thyroid blood tests helps keep your hormone levels stable, which may improve erectile function and overall health. Always tell your prescriber about your thyroid condition when requesting tadalafil.
Scientific References
- NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 22 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 22 October 2026]
- Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 22 October 2026]
- Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 22 October 2026]
- Electronic Medicines Compendium. (n.d.). Summaries of Product Characteristics and Patient Information Leaflets. https://www.medicines.org.uk/emc/ [accessed 22 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.
ED Treatments We Offer
Pricing Disclaimer: Prices on some pages may not be up to date — the live pricing table below and pricing shown during consultation are official current prices and take precedence over any other figures on the site.
Not sure which one? Start a free consultation →
Your Questions Answered
Can I take tadalafil if I take levothyroxine?
Yes, no major interaction between tadalafil and levothyroxine is commonly reported, and many men take both safely. Always declare all your medicines during your consultation so your prescriber can check for any other interactions.
Will levothyroxine affect how well tadalafil works?
Levothyroxine itself does not reduce the effectiveness of tadalafil. However, if your thyroid levels are not well controlled, this can contribute to ED, so keeping your thyroid function stable may help improve results.
Do I need to take tadalafil and levothyroxine at different times?
No special timing is needed between tadalafil and levothyroxine. Take levothyroxine as directed (usually in the morning on an empty stomach) and tadalafil as prescribed for ED.
Can hypothyroidism cause erectile dysfunction?
Yes, an underactive thyroid (hypothyroidism) is a recognised cause of erectile dysfunction. Treating it with levothyroxine can help improve ED symptoms once thyroid levels are stable.
What should I tell my prescriber about my thyroid condition?
Tell your prescriber that you take levothyroxine, what dose you take, and whether your thyroid function is well controlled. This helps them assess whether tadalafil is suitable and likely to work well for you.
Are there any medicines I must not take with tadalafil?
Yes. Never take tadalafil with nitrates (GTN spray, isosorbide mononitrate or dinitrate), nicorandil, riociguat, or poppers, as this can cause a dangerous drop in blood pressure. Declare all your medicines during your consultation.
Can I drink alcohol while taking tadalafil and levothyroxine?
Small amounts of alcohol are usually fine, but heavy drinking can worsen ED and add to the blood-pressure-lowering effect of tadalafil. Alcohol does not interact with levothyroxine.
What should I do if tadalafil does not work for me?
Speak to your prescriber. They may adjust your dose, check whether your thyroid is well controlled, or suggest trying a different ED medicine. Do not take more than the prescribed dose.
Trusted by thousands
Real people, real results
“Fabulous service and quick delivery”
“Felt the effects of these after about 5 days. Erections are better and can get aroused and ready easier”
“Excellent value and brilliant customer service”
“I received excellent service and everything went well. The order arrived quickly and in perfect condition. It's working very well! Thank you to the whole team for the great work!”
“Delivery was good, the product lived up to expectations.”
How Our Online Service Works
Choose your treatment
Select from our recommended UK-licensed medications.
Answer quick questions
Select safe UK treatments. Quick answers.
Get it delivered fast
We will deliver direct to you as quickly as tomorrow.
Get Discreet ED Treatment Online
- Reviewed by UK-based prescribers
- Takes under 3 minutes
- Discreet Packaging
Medically reviewed by
Tarun Kumar, Superintendent Pharmacist (GPhC 2233073)