Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor widely prescribed in the UK for erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension. Understanding how tadalafil works helps patients use this medication safely and effectively. By inhibiting the PDE5 enzyme, tadalafil promotes smooth muscle relaxation and increases blood flow to targeted areas of the body. This mechanism enables men to achieve erections during sexual stimulation, relieves urinary symptoms from an enlarged prostate, and reduces pulmonary blood pressure. This article explains tadalafil's mechanism of action, onset times, factors affecting efficacy, and what to expect during treatment.

What Is Tadalafil and What Conditions Does It Treat?

Tadalafil is a prescription medication belonging to a class of drugs known as phosphodiesterase type 5 (PDE5) inhibitors. It works by relaxing smooth muscle tissue and increasing blood flow to specific areas of the body. The Medicines and Healthcare products Regulatory Agency (MHRA) has approved tadalafil for several clinical indications in the UK.

The primary licensed uses of tadalafil include:

• Erectile dysfunction (ED) – helping men achieve and maintain an erection sufficient for sexual activity

• Benign prostatic hyperplasia (BPH) – relieving urinary symptoms associated with an enlarged prostate gland

• Pulmonary arterial hypertension (PAH) – reducing elevated blood pressure in the arteries of the lungs (specialist-only prescribing)

Tadalafil is available under various brand names in the UK, with specific products for different indications:

• Cialis for ED and BPH

• Adcirca specifically for PAH

• Generic versions are also widely available

The medication comes in different strengths with specific licensed dosing contexts:

• ED (on-demand): typically 10 mg (adjustable to 5-20 mg) taken before sexual activity

• ED (daily): 2.5-5 mg once daily

• BPH: 5 mg once daily

• PAH: 40 mg once daily (as Adcirca, under specialist supervision)

Mechanism of action: Tadalafil inhibits the PDE5 enzyme, which normally breaks down cyclic guanosine monophosphate (cGMP). By blocking this enzyme, tadalafil allows cGMP levels to remain elevated, promoting smooth muscle relaxation and vasodilation. In erectile dysfunction, this enhances blood flow to the penile tissue during sexual stimulation. For BPH, it relaxes smooth muscle in the prostate and bladder, improving urinary symptoms without reducing prostate size. In PAH, it dilates pulmonary blood vessels, reducing the workload on the heart.

It is important to note that tadalafil requires a prescription in the UK and should only be taken under medical supervision following appropriate assessment by a healthcare professional. The different formulations are not interchangeable, particularly between ED/BPH treatment and PAH management.

How Long Does Tadalafil Take to Work?

The onset of action for tadalafil varies depending on the condition being treated and the dosing regimen prescribed. Understanding these timelines helps patients set realistic expectations and use the medication most effectively.

For erectile dysfunction (on-demand dosing):

When taken as needed before sexual activity, tadalafil typically begins to work within 30 to 60 minutes for most men. The medication reaches peak plasma concentrations approximately 2 hours after ingestion. Importantly, sexual stimulation is required for tadalafil to produce an erection – it does not cause automatic arousal or erections.

One distinctive feature of tadalafil compared to other PDE5 inhibitors is its prolonged duration of action, which can last up to 36 hours. This extended window allows for greater spontaneity in sexual activity without the need for precise timing.

For erectile dysfunction (daily dosing):

When prescribed as a daily low-dose regimen (2.5 mg or 5 mg), tadalafil builds up to steady levels in the bloodstream. Patients may notice optimal effects after 4 to 5 days of consistent daily use, as the medication reaches therapeutic concentrations.

For benign prostatic hyperplasia:

When treating BPH symptoms, improvements in urinary flow and symptom relief typically become noticeable within 1 to 2 weeks of starting daily tadalafil therapy, though maximum benefits may take up to 4 weeks.

For pulmonary arterial hypertension:

In PAH treatment, clinical improvements in exercise capacity and haemodynamic parameters generally develop over several weeks of regular daily dosing under specialist supervision.

Patients should follow their prescriber's specific instructions regarding timing and should not adjust doses without medical consultation.

Factors That Affect How Well Tadalafil Works

Several physiological, lifestyle, and medication-related factors can influence tadalafil's effectiveness. Understanding these variables helps optimise treatment outcomes and manage expectations appropriately.

Food and alcohol intake:

Unlike some other PDE5 inhibitors, tadalafil absorption is not significantly affected by food, meaning it can be taken with or without meals. However, consuming excessive alcohol may impair erectile function independently and can increase the risk of side effects such as dizziness, headache, and hypotension. The NHS advises limiting alcohol consumption when using tadalafil.

Grapefruit and grapefruit juice can increase tadalafil levels in the blood by inhibiting its metabolism, potentially increasing the risk of side effects. It's advisable to avoid grapefruit products while taking tadalafil.

Underlying health conditions:

The effectiveness of tadalafil can be influenced by:

• Cardiovascular disease – conditions affecting blood flow may reduce response

• Diabetes mellitus – can cause vascular and nerve damage affecting erectile function

• Hormonal imbalances – particularly low testosterone levels

• Neurological disorders – such as multiple sclerosis or spinal cord injury

• Psychological factors – anxiety, depression, or relationship issues may limit effectiveness

• Renal or hepatic impairment – may increase tadalafil exposure and require dose adjustment

Medication interactions:

Certain medications can affect how tadalafil works or increase the risk of adverse effects:

• Nitrates (e.g., glyceryl trinitrate) – absolute contraindication due to severe hypotension risk

• Recreational nitrates ('poppers' like amyl nitrite) – dangerous combination that can cause severe hypotension

• Guanylate cyclase stimulators (e.g., riociguat) – absolute contraindication due to additive hypotensive effects

• Alpha-blockers – may cause additive blood pressure lowering; combination not recommended for BPH treatment; for ED, ensure stable on alpha-blocker and start at lowest tadalafil dose

• Other antihypertensives – potential for enhanced hypotensive effects

• CYP3A4 inhibitors (e.g., ketoconazole, ritonavir) – increase tadalafil levels; daily dosing may be unsuitable and on-demand dosing frequency may need restriction

• CYP3A4 inducers (e.g., rifampicin) – may reduce tadalafil effectiveness

Dosage and adherence:

Using the appropriate dose for your specific condition is crucial. Some men may require dose adjustment after initial trials. For daily dosing regimens, consistent adherence is essential for maintaining therapeutic drug levels.

Severity of erectile dysfunction:

Men with severe ED, particularly when caused by significant vascular disease or nerve damage, may experience reduced response rates compared to those with mild to moderate ED.

Smoking and lifestyle factors:

Cigarette smoking damages blood vessels and is associated with reduced tadalafil efficacy. Regular physical activity, maintaining a healthy weight, and managing stress can all improve treatment outcomes.

Patients experiencing suboptimal results should discuss these factors with their GP or specialist rather than increasing doses independently.

What to Expect When Taking Tadalafil

Understanding what to expect when starting tadalafil helps patients use the medication safely and recognise when medical advice is needed.

Common side effects:

Most men tolerate tadalafil well, but some may experience mild to moderate adverse effects, including:

• Headache – the most frequently reported side effect

• Indigestion or dyspepsia – stomach discomfort or acid reflux

• Back pain and muscle aches – typically occurring 12 to 24 hours after dosing and resolving within 48 hours

• Facial flushing – warmth or redness in the face and neck

• Nasal congestion – stuffy or runny nose

• Dizziness – particularly when standing up quickly

These effects are generally mild and transient, often diminishing with continued use. Taking the medication with adequate hydration may help reduce some symptoms.

Patients can report suspected side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Serious adverse effects requiring immediate medical attention:

Whilst rare, certain side effects warrant urgent medical assessment:

• Priapism – a painful erection lasting more than 4 hours is a medical emergency requiring immediate treatment (call 999 or go to A&E) to prevent permanent damage

• Sudden vision loss – may indicate non-arteritic anterior ischaemic optic neuropathy (NAION)

• Sudden hearing loss or tinnitus – requires prompt evaluation

• Chest pain during sexual activity – stop activity and seek immediate medical help (call 999 or go to A&E); do not take nitrates and inform healthcare staff you have taken tadalafil

• Severe allergic reactions – rash, swelling, difficulty breathing

Practical guidance for patients:

When starting tadalafil for erectile dysfunction, NICE guidance suggests:

• Allow adequate time for the medication to work (at least 30–60 minutes before sexual activity for on-demand dosing)

• Try the medication on around 8 separate occasions before concluding it is ineffective, as response may improve with repeated use

• Ensure adequate sexual stimulation, as tadalafil facilitates but does not initiate erections

• Store tablets at room temperature away from moisture

When to contact your GP:

Patients should seek medical review if:

• The medication is ineffective after several attempts at the prescribed dose

• Side effects are troublesome or persistent

• New symptoms develop

• There are concerns about interactions with other medications

• Erectile dysfunction worsens or changes in character

Safety considerations:

Tadalafil should not be used by individuals taking nitrates for angina, recreational nitrates ('poppers'), or guanylate cyclase stimulators (e.g., riociguat). It is also contraindicated in those with severe cardiovascular disease where sexual activity is inadvisable. Men with anatomical penile abnormalities, bleeding disorders, or active peptic ulcers should discuss these conditions with their prescriber.

Regular follow-up with healthcare providers ensures ongoing safety and allows for treatment optimisation. Patients should be open about their response to treatment and any concerns, as alternative therapies or dose adjustments may be appropriate. The goal is to find an effective, well-tolerated regimen that improves quality of life whilst maintaining safety.

Frequently Asked Questions