Tadalafil: What it is, how it works, and what to expect

DoktorABC editorial team

Accurate, up-to-date health information written by our editorial team and reviewed by UK-registered prescribers.

What is tadalafil?

Tadalafil is a prescription medicine belonging to a class of drugs called PDE5 inhibitors. It was originally developed by Eli Lilly under the brand name Cialis and first approved in the UK in 2003. Generic tadalafil has been available in the UK since 2018, following patent expiry, and is now the more widely prescribed form.

Tadalafil is available in the UK under several names:

• Cialis: The original branded version, manufactured by Eli Lilly
• Generic tadalafil: Available from multiple MHRA-approved manufacturers at significantly lower cost, containing the same active ingredient at the same doses
• Adcirca: A higher-dose branded formulation used for pulmonary arterial hypertension, managed by specialists

How tadalafil works

Tadalafil works by inhibiting an enzyme called PDE5, which is found predominantly in the smooth muscle tissue of the penis. During sexual arousal, the body releases nitric oxide into the penile tissue. Nitric oxide triggers the production of a chemical called cyclic GMP (cGMP), which relaxes the smooth muscle in the walls of the blood vessels in the penis. This relaxation allows blood to flow in, producing an erection.

PDE5 is the enzyme responsible for breaking down cGMP, which limits and eventually ends the erection response. In men with ED, PDE5 activity can be excessive or the cGMP response insufficient, meaning the blood flow needed for an erection does not happen effectively or does not last.

Tadalafil blocks PDE5, allowing cGMP to accumulate and sustain the blood flow needed for an erection in response to sexual stimulation.

What is tadalafil used for?

Tadalafil is licensed in the UK for three distinct indications, which is more than any other PDE5 inhibitor currently available. While most men taking tadalafil are doing so for erectile dysfunction, it is worth understanding the full scope of its licensed uses, particularly for those managing more than one condition simultaneously. 

Erectile dysfunction

This is by far the most common use. Tadalafil is prescribed for men who are unable to achieve or maintain an erection sufficient for satisfactory sexual activity. It is available both as an on-demand dose (10 mg or 20 mg, taken before sexual activity) and as a daily low dose (2.5 mg or 5 mg), which maintains a consistent level of the drug in the body without the need to plan around taking a tablet.

Benign prostatic hyperplasia

Tadalafil 5 mg once daily is also licensed for the treatment of lower urinary tract symptoms associated with benign prostatic hyperplasia (BPH), an enlarged prostate. This makes it a practical option for men managing both ED and BPH simultaneously, as a single daily tablet addresses both conditions. The mechanism by which tadalafil helps urinary symptoms is discussed in more detail below.

Pulmonary arterial hypertension

At higher doses (typically 40 mg once daily), tadalafil is used under specialist supervision for pulmonary arterial hypertension (PAH), a serious condition involving high blood pressure in the arteries of the lungs. For this indication, it is typically prescribed under the brand name Adcirca rather than Cialis.

How long does tadalafil take to work?

For most men, tadalafil begins to work within 30 to 60 minutes of taking an on-demand dose. It is generally recommended to take it at least 30 minutes before sexual activity, though many men find allowing a full hour produces the most reliable onset.

Several factors influence how quickly tadalafil takes effect:

• Food: Unlike sildenafil, tadalafil is not meaningfully affected by food. It can be taken with or without a meal without significantly altering the onset or peak effect, which is one of its practical advantages over sildenafil.
• Alcohol: Heavy alcohol consumption can delay onset and worsen side effects. Modest consumption is generally tolerable for most men.
• Age: Older men clear tadalafil more slowly, which can mean a slightly delayed onset but also a more prolonged duration of action.
• Individual metabolism: Response time varies between men. Some notice an effect within 20 to 30 minutes; others may need closer to 90 minutes.

How long does tadalafil last?

This is the most clinically distinctive feature of tadalafil and the aspect that most frequently drives men to choose it over sildenafil.

Tadalafil has a half-life of approximately 17.5 hours, roughly four times longer than sildenafil's three to five hours. In practical terms, a single on-demand dose can support the ability to achieve an erection in response to arousal for up to 36 hours. This is why tadalafil is sometimes informally referred to as the "weekend pill."

The extended duration does not mean a continuous erection for 36 hours. It means that the physiological support for an erection in response to arousal remains present throughout that window.

Does tadalafil lower blood pressure?

Yes, modestly and transiently. Tadalafil's vasodilatory mechanism produces a mild reduction in blood pressure as a pharmacological effect. For most men this is well tolerated and does not cause noticeable symptoms.

The clinical concern arises in two specific situations.

The first is the combination with nitrate medicines. Tadalafil is absolutely contraindicated alongside any form of nitrate, including glyceryl trinitrate (GTN) spray, isosorbide mononitrate, and isosorbide dinitrate. The combination of two vasodilatory mechanisms can cause a severe and potentially life-threatening drop in blood pressure.

The second is the combination with antihypertensive medicines or alpha-blockers, where an additive blood pressure-lowering effect can occur. This does not automatically preclude use but requires careful prescriber assessment before starting.

Key benefits of tadalafil compared to other ED medicines

Tadalafil shares the same basic mechanism as sildenafil and vardenafil, but differs in ways that matter practically for many men.

• Extended duration: The 36-hour window is the most significant distinguishing feature. It removes the need to plan precisely around taking a tablet, which many men describe as meaningfully improving their experience and reducing performance-related anxiety
• No food interaction: Tadalafil can be taken with or after a meal without affecting absorption, unlike sildenafil which is significantly delayed by high-fat food
• Daily dosing option: No other on-demand ED medicine has a licensed daily low-dose regimen. The 2.5 mg and 5 mg daily options allow continuous background effectiveness without any planning requirement
• Dual indication for BPH: For men managing both ED and urinary symptoms from an enlarged prostate, daily tadalafil addresses both with a single tablet
• Predictable side effect profile: Back pain and muscle aches are more commonly associated with tadalafil than sildenafil, while visual side effects are less common. For men who experience visual disturbances with sildenafil, tadalafil may be better tolerated

Who can and cannot take tadalafil

A medical assessment is required before starting tadalafil. The following is an overview of the key contraindications and cautions.

Tadalafil must not be taken by men who:

• Are taking nitrate medicines in any form
• Are taking riociguat (used for pulmonary hypertension)
• Have been advised that sexual activity is inadvisable due to cardiovascular risk
• Have had a stroke or heart attack within the last three to six months
• Have severe liver impairment
• Have hypotension (resting blood pressure below 90/50 mmHg)
• Have known hereditary degenerative retinal disorders such as retinitis pigmentosa
• Have previously experienced vision loss in one eye due to non-arteritic anterior ischaemic optic neuropathy (NAION)

Tadalafil should be used with caution and only after careful prescriber assessment in men with significant cardiovascular disease, those taking antihypertensive medicines or alpha-blockers, and those with moderate kidney or liver impairment.

Tadalafil for benign prostatic hyperplasia

For men with lower urinary tract symptoms caused by an enlarged prostate, daily tadalafil 5 mg has a licensed indication alongside its use for ED.

BPH causes urinary symptoms including difficulty starting urination, a weak or interrupted flow, frequent urination, and a feeling of incomplete bladder emptying. These symptoms occur because an enlarged prostate constricts the urethra and affects bladder muscle function.

Tadalafil helps by relaxing smooth muscle in the prostate and bladder neck through the same PDE5 inhibition mechanism that supports erectile function. This relaxation reduces the resistance to urine flow and improves bladder emptying, leading to meaningful improvements in urinary symptom scores in clinical trials.

How to get tadalafil in the UK

Tadalafil is a prescription-only medicine in the UK. There are two main routes to access.

Via your GP: 

Your GP can prescribe generic tadalafil on the NHS where it meets prescribing criteria for ED or BPH. NHS prescriptions are subject to the standard prescription charge in England and are free for eligible patients in Scotland, Wales, and Northern Ireland.

Via a regulated online clinic: 

Private online clinics connect you with UK-registered prescribers who can assess your suitability and issue a private prescription for tadalafil at any licensed dose. DoktorABC connects UK patients with licensed prescribers and GPhC-registered pharmacies for private ED treatment, with a full medical assessment completed online.

Final thoughts

Tadalafil is a well-established, extensively studied medicine with a distinctive clinical profile that suits many men with erectile dysfunction. Its extended duration, flexibility of dosing, and practical advantages around food and timing make it a meaningful alternative to shorter-acting PDE5 inhibitors for those who value spontaneity and convenience.

As with any prescription medicine, the starting point is a proper medical assessment. A UK-registered prescriber can review your health history, discuss the most appropriate dose and regimen, and ensure tadalafil is safe for your individual circumstances.

FAQ

The DoktorABC medical advisory board

Dr. Roland Ruiken

Medical advisor, Norway

Dr. Viktor Simunovic

Medical advisor, Croatia

To the medical advisory board