Tadalafil and Melatonin: Can You Take Them Together?
Learn about safety, interactions, and what your UK prescriber checks before treatment.
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How it Works?
Tadalafil and Melatonin: Understanding the Interaction
Published: 23 October 2026
Many men wonder whether tadalafil and melatonin can be taken together, especially if they use melatonin for sleep and tadalafil for erectile dysfunction. The good news is that no major direct interaction between tadalafil and melatonin is commonly reported in clinical practice. However, both medicines can affect blood pressure and alertness in different ways, so it's important to understand how they work, what your prescriber will check, and the practical steps to use them safely.
At a glance
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 [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 tablets (2.5mg or 5mg taken once a day) [4].
Tadalafil does not cause an erection on its own—you need sexual stimulation for it to work [1]. It can help men achieve and maintain an erection suitable for sexual activity when ED is present. Common side effects include headache, indigestion, back pain, muscle aches, flushing, and nasal congestion [4]. Tadalafil is only available on prescription in the UK after a consultation with a healthcare professional, who will check your medical history and current medicines to ensure it is safe for you.
What is melatonin and why do people take it?
Melatonin is a hormone naturally produced by the pineal gland in the brain that helps regulate your sleep-wake cycle. Synthetic melatonin is available as a medicine or supplement to treat sleep problems, particularly difficulty falling asleep or staying asleep. In the UK, melatonin is a prescription-only medicine for adults aged 55 and over (brand name Circadin, 2mg prolonged-release tablets) and for children with certain sleep disorders. Lower-dose melatonin supplements (typically 1–3mg) are also sold as food supplements without prescription.
Melatonin works by mimicking the natural hormone, signalling to your body that it is time to sleep. It is usually taken 1–2 hours before bedtime. Common side effects can include drowsiness, headache, dizziness, and mild changes in blood pressure. Because melatonin can cause drowsiness and affect alertness, it is important to consider how it might interact with other medicines you take, including those for erectile dysfunction.
Do tadalafil and melatonin interact with each other?
There is no well-documented direct pharmacological interaction between tadalafil and melatonin. They work through different mechanisms in the body: tadalafil acts on blood vessels via the PDE5 enzyme, while melatonin acts on receptors in the brain that regulate sleep. No major interaction is commonly reported in clinical practice or listed in standard UK drug interaction resources [4].
However, both medicines can have effects that may overlap in certain ways. Tadalafil can cause a mild drop in blood pressure, particularly when you stand up, leading to dizziness or light-headedness [4]. Melatonin can also occasionally affect blood pressure and may cause drowsiness or dizziness. If you take both medicines, especially when starting or adjusting doses, be aware of these potential additive effects. It is always important to tell your prescriber about all medicines, supplements, and over-the-counter products you use, including melatonin, so they can assess your individual situation and advise you appropriately.
What the prescriber checks during your consultation
When you request tadalafil through an online consultation at Cured Pharmacy, a UK-registered prescriber will review your medical history, current medicines (including supplements like melatonin), and any health conditions. They will check for contraindications—medicines or conditions that make tadalafil unsafe, such as nitrates, nicorandil, riociguat, or recent heart problems [4]. They will also assess whether other medicines you take might interact with tadalafil or require a dose adjustment, such as alpha-blockers or potent CYP3A4 inhibitors [4]. If you are taking melatonin, mention it in your consultation so the prescriber can consider any relevant factors, such as drowsiness or blood pressure effects, and ensure the combination is appropriate for you.
What you need to know
- No major direct interaction is commonly reported between tadalafil and melatonin.
- Both medicines can cause dizziness; be cautious when standing, especially when starting treatment.
- Always tell your prescriber about all medicines and supplements, including melatonin.
- Never take tadalafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor.
- Seek urgent help for an erection lasting over 4 hours or sudden vision or hearing loss.
Medicines that should never be taken with tadalafil
While tadalafil and melatonin do not have a major interaction, there are some medicines and substances you must never take with tadalafil because the combination can cause a dangerous drop in blood pressure [4]. Do not take tadalafil if you are using nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate for angina), nicorandil (another angina medicine), riociguat (for pulmonary hypertension), or recreational drugs known as 'poppers' (amyl or alkyl nitrites) [4]. Do not take tadalafil together with another PDE5 inhibitor, such as sildenafil (Viagra), vardenafil (Levitra), or avanafil (Spedra) [4].
If you take alpha-blockers for an enlarged prostate or high blood pressure (such as doxazosin, tamsulosin, or alfuzosin), there is a risk of low blood pressure and dizziness when combined with tadalafil [4]. Your prescriber will check that you are stable on the alpha-blocker and may start you on a lower dose of tadalafil. Potent CYP3A4 inhibitors (including ritonavir, cobicistat, ketoconazole, itraconazole, and clarithromycin) can increase tadalafil levels in your blood, so dose adjustments or caution are needed [4]. Always declare every medicine and supplement you take during your consultation.
Other medicines and lifestyle factors to consider
Other blood-pressure-lowering medicines can add to the blood-pressure effects of tadalafil, potentially causing dizziness, but this is usually manageable and must be assessed by your prescriber [4]. CYP3A4 inducers, such as rifampicin, carbamazepine, phenytoin, and St John's wort, can reduce tadalafil levels and make it less effective [4]. Grapefruit juice can increase tadalafil levels and should be avoided or limited. Heavy alcohol can worsen erectile dysfunction and add to the blood-pressure-lowering effect of tadalafil, so it is best to drink in moderation [1]. If you are taking any medicine not listed here, do not assume the combination is safe—your prescriber and pharmacist will check every current medicine during your consultation.
Practical advice for taking tadalafil and melatonin safely
If your prescriber confirms that tadalafil is suitable for you and you also take melatonin, here are some practical tips. Take each medicine as directed: melatonin is usually taken 1–2 hours before bedtime, while on-demand tadalafil is taken at least 30 minutes before sexual activity (or daily tadalafil is taken once a day at the same time) [4]. Because melatonin can cause drowsiness, avoid driving or operating machinery if you feel sleepy. If you experience dizziness or light-headedness, particularly when standing up, sit or lie down until it passes—this can happen with either medicine.
Monitor how you feel when you first start taking both medicines together. If you notice unusual dizziness, fainting, or any other concerning symptoms, contact your GP or pharmacist for advice. Do not stop or change a prescribed medicine without consulting a healthcare professional. If you buy melatonin as a supplement, remember that supplements are not regulated in the same way as medicines, so quality and dose can vary. Always tell your prescriber about any supplements you take, including melatonin, during your consultation for tadalafil.
When to get urgent help
- Erection lasting more than 4 hours (priapism)—go to A&E immediately
- Sudden loss of vision or hearing—stop tadalafil and seek urgent medical advice
- Chest pain during or after sex—call 999; do not use nitrate medicines if you have taken tadalafil
- Severe dizziness, fainting, or feeling very unwell—seek same-day medical advice
- Allergic reaction (rash, swelling, difficulty breathing)—call 999
Call 999 or go to A&E in an emergency, or contact NHS 111 for urgent advice.
When to seek urgent help and next steps
Most men tolerate tadalafil well, but you should seek urgent medical help in certain situations. If you have an erection lasting more than 4 hours (priapism), go to A&E immediately, as this can cause permanent damage [4]. If you experience sudden loss of vision or hearing, stop taking tadalafil and seek urgent medical advice [4]. If you develop chest pain during or after sex, do not use nitrate medicines (such as GTN spray) to treat it if you have taken tadalafil—call 999 and tell the paramedics you have taken tadalafil [4]. If you feel very dizzy, faint, or unwell after taking tadalafil and melatonin together, seek same-day medical advice.
If you have new or worsening erectile dysfunction, see your GP for a full assessment, as ED can be an early sign of underlying health conditions such as heart disease or diabetes [1]. At Cured Pharmacy, our online consultation is reviewed by a UK-registered prescriber who will check your suitability for tadalafil and answer any questions about interactions, including with melatonin. Prescription treatments are only supplied after clinical assessment, ensuring your safety and the appropriateness of the medicine for you.
How Cured Pharmacy can help
Cured Pharmacy is a GPhC-registered online pharmacy (GPhC 9012511) offering discreet, convenient access to erectile dysfunction treatments. After completing a short online consultation, a UK-registered prescriber will review your answers, check for interactions (including with melatonin and other medicines), and issue a prescription if tadalafil is suitable for you. Your medicine is then dispensed by our pharmacy team and delivered discreetly to your door. We offer a range of ED treatments, including generic and branded options, with clear pricing and no hidden fees. If you have questions about tadalafil and melatonin or any other interaction, our pharmacist-led team is here to help.
Always declare melatonin in your consultation
Even though no major interaction is reported, your prescriber needs to know about all medicines and supplements you take—including melatonin—to assess your individual safety and advise you properly.
Scientific References
- NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 23 October 2026]
- Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 23 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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Can I take tadalafil and melatonin on the same day?
Yes, there is no major direct interaction between tadalafil and melatonin, so they can generally be taken on the same day. Always mention melatonin in your consultation so your prescriber can assess your individual situation.
Will melatonin make tadalafil less effective?
No, melatonin does not reduce the effectiveness of tadalafil. They work through different mechanisms and do not interfere with each other's action.
Can taking tadalafil and melatonin together cause low blood pressure?
Both medicines can occasionally affect blood pressure, so there is a theoretical risk of additive effects such as dizziness. This is usually mild and manageable, but mention both medicines in your consultation so your prescriber can advise you.
Do I need to tell my prescriber I take melatonin?
Yes, always tell your prescriber about all medicines, supplements, and over-the-counter products you take, including melatonin. This helps them assess your suitability for tadalafil and check for any interactions.
Can I take tadalafil if I use over-the-counter melatonin supplements?
Yes, over-the-counter melatonin supplements do not prevent you from taking tadalafil. Declare the supplement in your consultation so your prescriber can consider it in their assessment.
What should I do if I feel dizzy after taking tadalafil and melatonin?
Sit or lie down until the dizziness passes. If it is severe, persistent, or you feel faint, contact your GP or pharmacist for advice the same day.
Are there any medicines I must never take with tadalafil?
Yes, do not take tadalafil with nitrates, nicorandil, riociguat, poppers, or another PDE5 inhibitor, as the combination can cause a dangerous drop in blood pressure. Always declare all your medicines during your consultation.
How do I get tadalafil from Cured Pharmacy?
Complete a short online consultation, which will be reviewed by a UK-registered prescriber. If tadalafil is suitable for you, a prescription will be issued, and your medicine will be dispensed and delivered discreetly to your door.
Medically reviewed by
Tarun Kumar, Superintendent Pharmacist (GPhC 2233073)