How Does Tadalafil Work to Treat ED?

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How Does Tadalafil Work to Treat Erectile Dysfunction?

Published: 7 November 2026

How does tadalafil work? Tadalafil works by blocking an enzyme called phosphodiesterase type 5 (PDE5), which allows blood vessels in the penis to relax and widen during sexual stimulation, making it easier to achieve and maintain an erection. Unlike some other erectile dysfunction treatments, tadalafil has a particularly long duration of action—up to 36 hours—which is why it's often called the 'weekend pill'. Understanding how tadalafil works can help you decide whether it's the right treatment option for you.

The Science Behind How Tadalafil Works

To understand how tadalafil works, it helps to know what happens during a normal erection. When you're sexually aroused, nerve signals trigger the release of a chemical called nitric oxide in the penis. This nitric oxide activates an enzyme that produces cyclic guanosine monophosphate (cGMP), a molecule that relaxes the smooth muscle in the blood vessels of the penis, allowing them to widen and fill with blood [1].

After ejaculation or when arousal fades, another enzyme called phosphodiesterase type 5 (PDE5) breaks down cGMP, causing the blood vessels to narrow again and the erection to subside. In men with erectile dysfunction, this process doesn't work efficiently—often because there isn't enough cGMP to maintain an erection [2].

Tadalafil belongs to a class of medicines called PDE5 inhibitors. By blocking the PDE5 enzyme, tadalafil prevents the breakdown of cGMP, allowing it to accumulate and keep blood vessels relaxed for longer. This makes it easier to get and keep an erection when you're sexually stimulated [4]. It's important to note that tadalafil doesn't cause an erection on its own—you still need sexual stimulation for it to work.

How Long Does Tadalafil Take to Work and How Long Does It Last?

One of the key features that sets tadalafil apart from other erectile dysfunction medicines is its long duration of action. When taken on-demand, tadalafil typically starts to work within 30 minutes to an hour, though it can take up to 2 hours for some men. The effects can last for up to 36 hours, which means you don't need to time sex as precisely as you would with shorter-acting treatments like sildenafil [4].

This extended window is why tadalafil is sometimes referred to as the 'weekend pill'—a single dose taken on Friday evening could potentially be effective through Sunday. However, this doesn't mean you'll have an erection for 36 hours; it simply means the medicine remains in your system and can help you achieve an erection during that time when you're sexually aroused.

Tadalafil is also available as a daily low-dose option (2.5mg or 5mg), which you take every day at the same time regardless of when you plan to have sex. This approach maintains a steady level of the medicine in your body, allowing for more spontaneity [4]. The daily option may be suitable if you have sex more than twice a week or prefer not to plan ahead.

On-Demand vs Daily Tadalafil: Which Works Better?

Both approaches work through the same mechanism, but they suit different lifestyles. On-demand tadalafil (10mg or 20mg) is taken at least 30 minutes before sexual activity and is ideal if you have sex less frequently or prefer to take medicine only when needed. Daily tadalafil (2.5mg or 5mg) is taken every day and may be better if you want the flexibility to be intimate without planning ahead [4].

Neither approach is inherently 'better'—it depends on your personal circumstances, how often you have sex, and your preferences. Your prescriber will discuss which option is most suitable for you during your consultation. Some men find the daily dose reduces performance anxiety because they don't need to think about timing.

How Does Tadalafil Work Compared to Sildenafil (Viagra)?

Both tadalafil and sildenafil are PDE5 inhibitors, so they work through the same basic mechanism: blocking the PDE5 enzyme to increase cGMP levels and improve blood flow to the penis during sexual stimulation. The main differences lie in how quickly they work and how long they last [3][4].

Sildenafil (the active ingredient in Viagra) typically starts working within 30 to 60 minutes and lasts for about 4 to 6 hours. This makes it a good choice if you want a shorter window of effectiveness or prefer to take medicine closer to the time you plan to have sex. Tadalafil, on the other hand, can last up to 36 hours, offering a much longer window of opportunity [4].

Some men find sildenafil works faster for them, while others prefer the extended duration of tadalafil. There's no single 'best' option—it's about finding what fits your lifestyle and body. Food can affect sildenafil more than tadalafil; a heavy, high-fat meal may delay sildenafil's onset, whereas tadalafil can be taken with or without food with minimal impact [3][4]. Both medicines require sexual stimulation to work and should not be taken more than once in 24 hours.

Does Tadalafil Work for Everyone with Erectile Dysfunction?

Tadalafil is effective for many men with erectile dysfunction, but it doesn't work for everyone. Clinical trials have shown that PDE5 inhibitors like tadalafil can help a significant proportion of men achieve erections firm enough for sex, but individual results vary depending on the underlying cause of ED and other health factors [4].

Tadalafil tends to work best when erectile dysfunction is caused by physical factors such as reduced blood flow, which is common in men with diabetes, high blood pressure, or heart disease. It may be less effective if ED is primarily due to psychological factors like anxiety or depression, though it can still help in some cases. Combining tadalafil with counselling or therapy may improve outcomes when psychological factors are involved [2].

Certain health conditions and medicines can affect how well tadalafil works or whether it's safe to use. For example, men taking nitrates for angina, nicorandil, or riociguat must never take tadalafil, as the combination can cause a dangerous drop in blood pressure. Men on alpha-blockers for prostate problems or high blood pressure need careful dose adjustment [4]. Your prescriber will review your full medical history and current medicines during your consultation to ensure tadalafil is safe and appropriate for you.

What If Tadalafil Doesn't Work for You?

If tadalafil doesn't work on the first attempt, don't give up. It can take several tries—sometimes up to eight attempts—for your body to respond optimally. Make sure you're taking it correctly: at least 30 minutes before sex, with sexual stimulation, and not more than once a day. Avoiding heavy alcohol and managing stress can also improve effectiveness [2].

If tadalafil still doesn't work after several attempts, speak to your prescriber. They may adjust your dose, suggest trying a different PDE5 inhibitor such as sildenafil or vardenafil, or explore other treatment options like alprostadil cream or injections, vacuum devices, or referral to a specialist. It's also important to see your GP if you haven't already, as erectile dysfunction can be an early warning sign of conditions like diabetes or heart disease [1][2].

How Does Tadalafil Work with Other Medicines and Health Conditions?

Tadalafil can interact with several other medicines, so it's essential to tell your prescriber about everything you're taking, including over-the-counter medicines, supplements, and recreational drugs. The most serious interaction is with nitrates (such as GTN spray, isosorbide mononitrate, or isosorbide dinitrate), nicorandil, riociguat, and amyl or alkyl nitrites (poppers). Taking tadalafil with any of these can cause a severe and potentially life-threatening drop in blood pressure [4].

Alpha-blockers, used for prostate enlargement or high blood pressure (such as tamsulosin, doxazosin, or alfuzosin), can also lower blood pressure when combined with tadalafil. If you take an alpha-blocker, you should be stable on it before starting tadalafil, and your prescriber will usually recommend starting with the lowest dose of tadalafil to minimise the risk of dizziness or fainting [4].

Medicines that affect liver enzymes can alter tadalafil levels in your blood. Potent CYP3A4 inhibitors—such as ritonavir, cobicistat (found in some HIV medicines), ketoconazole, itraconazole, and clarithromycin—can increase tadalafil levels, requiring dose adjustments. Conversely, CYP3A4 inducers like rifampicin, carbamazepine, phenytoin, and St John's wort can reduce tadalafil's effectiveness [4]. Grapefruit juice can also raise tadalafil levels and should be avoided. Your prescriber will check all your current medicines during your consultation to ensure tadalafil is safe for you.

How to Use Tadalafil Safely and Get the Best Results

To get the most from tadalafil, take it as directed by your prescriber. For on-demand use, take one tablet (usually 10mg or 20mg) at least 30 minutes before you plan to have sex. You can take it with or without food. Do not take more than one dose in 24 hours, even if the first dose didn't work as well as you hoped [4].

For daily tadalafil, take one low-dose tablet (2.5mg or 5mg) at the same time every day, whether or not you plan to have sex. This maintains a steady level of the medicine in your system. Remember that tadalafil only works when you're sexually aroused—it won't cause an automatic erection [4].

Avoid drinking excessive alcohol when using tadalafil, as alcohol can make it harder to get an erection and increase the risk of side effects like dizziness and headaches. A healthy lifestyle—maintaining a healthy weight, exercising regularly, not smoking, and managing stress—can improve how well tadalafil works and your overall sexual health [1][2]. If you experience side effects such as headache, indigestion, back pain, or muscle aches, these are usually mild and temporary. However, if you develop chest pain during sex, an erection lasting more than 4 hours, or sudden loss of vision or hearing, seek urgent medical help immediately.

When Should You See a Doctor About Erectile Dysfunction?

If you're experiencing erectile dysfunction for the first time or if it's getting worse, it's important to see your GP. ED can be an early warning sign of underlying health conditions such as diabetes, high blood pressure, high cholesterol, or heart disease [1][2]. Identifying and treating these conditions can improve both your general health and your erectile function.

Your GP can also check whether any medicines you're taking might be contributing to ED and explore whether psychological factors such as stress, anxiety, or depression are playing a role. Even if you're using an online service like Cured Pharmacy for treatment, seeing your GP for an initial assessment is a sensible step. All prescription treatments from Cured Pharmacy are provided after an online consultation reviewed by a UK-registered prescriber, ensuring the medicine is safe and suitable for you.

Scientific References

1. NHS. (n.d.). Erectile dysfunction (impotence). NHS website. https://www.nhs.uk/conditions/erection-problems-erectile-dysfunction/ [accessed 7 November 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 7 November 2026]
3. Joint Formulary Committee. (n.d.). Sildenafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/sildenafil/ [accessed 7 November 2026]
4. Joint Formulary Committee. (n.d.). Tadalafil. British National Formulary. NICE. https://bnf.nice.org.uk/drugs/tadalafil/ [accessed 7 November 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.