Does tadalafil cause diarrhoea? Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK for erectile dysfunction and benign prostatic hyperplasia. Whilst generally well tolerated, diarrhoea is classified as an uncommon adverse effect, occurring in fewer than 1 in 100 patients according to the Summary of Product Characteristics. Understanding the frequency, potential mechanisms, and management of gastrointestinal side effects helps patients and clinicians make informed decisions about treatment. This article examines the evidence surrounding tadalafil and diarrhoea, when to seek medical advice, and practical strategies for managing digestive symptoms whilst continuing therapy.

Does Tadalafil Cause Diarrhoea?

Tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor licensed in the UK for the treatment of erectile dysfunction and benign prostatic hyperplasia. Diarrhoea is classified as an uncommon adverse effect of tadalafil in the Summary of Product Characteristics (SmPC), occurring in fewer than 1 in 100 patients.

The mechanism by which tadalafil might theoretically contribute to gastrointestinal disturbances is not fully established. PDE5 inhibitors work primarily by enhancing blood flow through vasodilation, predominantly affecting vascular smooth muscle. PDE5 enzymes are also present in other tissues, including the gastrointestinal tract, which might potentially affect gut function, though this remains speculative.

In clinical practice, when patients report diarrhoea whilst taking tadalafil, it is important to consider alternative explanations. Gastrointestinal symptoms may arise from concurrent medications, dietary factors, infections, or underlying conditions such as irritable bowel syndrome. The temporal relationship between starting tadalafil and the onset of symptoms can help determine whether the medication is implicated.

Patients should be reassured that whilst diarrhoea can occur with tadalafil, it is generally self-limiting. Maintaining adequate hydration is important, as dehydration could potentially increase the risk of hypotension in patients taking PDE5 inhibitors. Persistent or severe gastrointestinal symptoms warrant further clinical assessment to exclude other causes.

If you experience side effects from any medication, you can report them through the MHRA Yellow Card Scheme, which helps monitor medicine safety.

How Common Is Diarrhoea with Tadalafil?

According to data from clinical trials and post-marketing surveillance, diarrhoea is classified as an uncommon adverse effect of tadalafil, occurring in fewer than 1 in 100 patients. The most frequently reported side effects of tadalafil include:

• Headache (affecting up to 1 in 10 patients)

• Dyspepsia or indigestion (up to 1 in 10 patients)

• Back pain and myalgia (up to 1 in 10 patients)

• Flushing (up to 1 in 10 patients)

• Nasal congestion (up to 1 in 10 patients)

Gastrointestinal side effects as a category are more commonly represented by dyspepsia rather than diarrhoea. The European Medicines Agency (EMA) and MHRA documentation list gastrointestinal disturbances among possible side effects, with varying frequencies.

The incidence of diarrhoea may vary depending on the dose of tadalafil prescribed. For benign prostatic hyperplasia, the licensed dose is 5 mg once daily, while for erectile dysfunction, doses range from 2.5-5 mg once daily (for regular use) to 10-20 mg (for on-demand use). However, robust comparative data specifically examining diarrhoea rates across different dosing regimens remain limited.

It is worth noting that individual susceptibility to medication side effects varies considerably. Factors such as age, concurrent medications, and underlying gastrointestinal conditions may influence whether a particular patient experiences diarrhoea. Healthcare professionals should consider these variables when counselling patients about potential adverse effects and should not dismiss patient-reported symptoms, even if they are statistically uncommon.

When to Seek Medical Advice About Diarrhoea

Whilst mild, transient diarrhoea may not require immediate medical intervention, certain features warrant prompt clinical assessment. Patients taking tadalafil should contact their GP or NHS 111 if they experience:

• Persistent diarrhoea lasting more than 7 days in adults

• Blood in the stool or black, tarry stools

• Signs of dehydration, including reduced urine output, dizziness, dry mouth, or excessive thirst

• Severe abdominal pain or cramping

• High fever accompanying diarrhoea

• Unintentional weight loss

These features may indicate conditions unrelated to tadalafil that require investigation. NICE guidance (NG12) recommends specific referral thresholds for persistent bowel symptoms, including for those aged 40+ with unexplained weight loss and abdominal pain, those 60+ with changes in bowel habit, or those 50+ with rectal bleeding.

Patients should inform their healthcare provider if diarrhoea develops after starting tadalafil, especially if it significantly impacts quality of life. A medication review may be appropriate to determine whether tadalafil is the likely cause or whether other factors could be responsible.

It's important to note that tadalafil has significant interactions with certain medications. It is contraindicated with nitrates, nicorandil and riociguat due to the risk of severe hypotension. Caution is needed when taking tadalafil with alpha-blockers, certain antifungals, and some HIV medications that affect CYP3A4 metabolism. Alcohol consumption should be limited as it may increase the risk of dizziness and hypotension.

Community pharmacists can provide initial advice about managing mild diarrhoea and whether it might be medication-related.

Managing Digestive Side Effects While Taking Tadalafil

For patients experiencing mild diarrhoea whilst taking tadalafil, several practical strategies may help manage symptoms whilst continuing treatment:

Dietary modifications can play a significant role in managing gastrointestinal symptoms. The NHS recommends:

• Eating small, light meals and avoiding fatty, spicy, or heavily processed foods

• Limiting caffeine intake, as this can stimulate bowel activity

• Avoiding alcohol, which can worsen diarrhoea and may increase the risk of hypotension when combined with tadalafil

• Focusing on foods containing soluble fibre such as bananas, rice, toast, and oats, which may help firm stools

Hydration is essential when experiencing diarrhoea. Patients should drink plenty of clear fluids, including water and oral rehydration solutions if symptoms are moderate. Dehydration can compound the discomfort associated with diarrhoea and may affect overall wellbeing.

Timing of medication may influence tolerability. While there is no strong evidence that taking tadalafil with food reduces gastrointestinal side effects, some patients report better tolerance with light meals. Food does not significantly affect tadalafil's absorption or efficacy.

Probiotics are sometimes suggested for managing medication-related digestive disturbances, though evidence specifically for tadalafil-associated diarrhoea is limited.

If conservative measures fail to resolve symptoms, healthcare professionals may consider dose adjustment or switching to an alternative PDE5 inhibitor such as sildenafil or vardenafil, which have slightly different pharmacological profiles. In cases of mild diarrhoea, over-the-counter loperamide may occasionally be appropriate for short-term use, though this should not be used if there is blood in the stool or high fever, and pharmacist or GP advice should be sought first.

Patients should maintain open communication with their healthcare provider about any side effects experienced. A collaborative approach ensures that treatment remains effective whilst minimising adverse effects.

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