Tadalafil is a widely prescribed phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction and benign prostatic hyperplasia in the UK. Whilst the medication is generally well-tolerated, patients sometimes wonder whether tadalafil causes constipation or other digestive symptoms. Understanding the established side effect profile of tadalafil, alongside practical management strategies for any gastrointestinal discomfort, helps patients use this medication safely and effectively. This article examines the evidence linking tadalafil to constipation, reviews recognised side effects, and provides guidance on when to seek medical advice.

What Is Tadalafil and How Does It Work?

Tadalafil is a prescription medication primarily used to treat erectile dysfunction (ED) and the urinary symptoms of benign prostatic hyperplasia (BPH). It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors, which also includes sildenafil and vardenafil. In the UK, tadalafil is available under brand names such as Cialis, as well as generic formulations approved by the Medicines and Healthcare products Regulatory Agency (MHRA).

The mechanism of action centres on the relaxation of smooth muscle tissue. Tadalafil works by inhibiting the PDE5 enzyme, which normally breaks down cyclic guanosine monophosphate (cGMP). When PDE5 is blocked, cGMP levels increase, leading to smooth muscle relaxation and improved blood flow. In erectile dysfunction, this enhanced blood flow to the penile tissues facilitates an erection in response to sexual stimulation. For BPH, the same mechanism helps relax smooth muscle in the prostate and bladder, easing urinary symptoms such as difficulty starting urination or weak stream.

Tadalafil is notable for its long duration of action—up to 36 hours—which distinguishes it from shorter-acting PDE5 inhibitors. It is available in different doses: lower daily doses (2.5 mg or 5 mg) for continuous use, and higher on-demand doses (10 mg or 20 mg) taken before anticipated sexual activity. The medication is absorbed through the gastrointestinal tract, with food having minimal effect on its absorption.

Important safety considerations include:

• Contraindications: Tadalafil must not be used with nitrates or nicorandil (medications for angina) due to dangerous blood pressure drops, or with riociguat (used for pulmonary hypertension)

• Interactions: Avoid grapefruit juice as it may increase tadalafil levels; use with caution alongside alpha-blockers (may cause blood pressure drops); and be aware that certain medications (including ketoconazole, ritonavir, rifampicin, carbamazepine) can significantly affect tadalafil levels

While tadalafil is generally well-tolerated, understanding its pharmacology helps patients recognise why certain side effects occur and how the medication interacts with the body's systems, including the digestive tract.

Common Side Effects of Tadalafil

Like all medications, tadalafil can cause side effects, though not everyone experiences them. The most frequently reported adverse effects are related to its vasodilatory properties—the widening of blood vessels throughout the body. Common side effects according to the UK product information include:

• Headache – very common (may affect more than 1 in 10 people)

• Flushing – common (may affect up to 1 in 10 people)

• Indigestion or dyspepsia – common (may affect up to 1 in 10 people)

• Nasal congestion – common (may affect up to 1 in 10 people)

• Back pain and muscle aches – common (may affect up to 1 in 10 people), typically appearing 12–24 hours after dosing

• Dizziness – common (may affect up to 1 in 10 people)

Regarding constipation specifically, there is no official link established between tadalafil and constipation in clinical trials or product literature approved by the MHRA or European Medicines Agency (EMA). Constipation is not listed among the common, uncommon, or rare side effects in the Summary of Product Characteristics for tadalafil. However, some patients do report digestive changes, which may be coincidental or related to other factors such as dietary changes, reduced physical activity, or concurrent medications.

Digestive symptoms that are recognised in the product information include dyspepsia (indigestion), abdominal pain, gastro-oesophageal reflux, and nausea. These gastrointestinal effects may possibly be related to PDE5 inhibitors affecting smooth muscle in the digestive tract, though the exact mechanism is not fully established. These effects are generally mild and transient, resolving without intervention.

If you experience persistent digestive symptoms whilst taking tadalafil, it is important to consider other potential causes and discuss them with your GP or pharmacist, as they may be unrelated to the medication itself.

Managing Digestive Symptoms While Taking Tadalafil

If you experience digestive discomfort, including constipation, whilst taking tadalafil, several practical strategies may help manage these symptoms effectively.

Dietary and lifestyle modifications form the foundation of managing digestive health:

• Increase fibre intake – Aim for around 30 grams daily through fruits, vegetables, whole grains, and legumes to promote regular bowel movements

• Maintain adequate hydration – Drink 6–8 glasses of water daily, as dehydration can contribute to constipation

• Regular physical activity – Even moderate exercise such as walking for 30 minutes daily can stimulate intestinal function

• Establish routine – Try to use the toilet at the same time each day, particularly after meals when the gastrocolic reflex is strongest

• Avoid trigger foods – Limit processed foods, excessive dairy, and foods known to cause personal digestive upset

Timing and administration considerations may also help. Taking tadalafil with or without food is generally acceptable, but if you experience indigestion, taking it with a light meal may help. Avoid lying down immediately after taking the medication, as this can exacerbate acid reflux symptoms.

For indigestion specifically, over-the-counter antacids may provide relief. While antacids may slightly affect tadalafil absorption, this effect is usually not clinically significant. Always check with your pharmacist about potential interactions before taking any new medicines, including over-the-counter products.

If constipation persists, short-term use of over-the-counter laxatives may be appropriate. Macrogol (polyethylene glycol) is often recommended as a first-line treatment, or you might consider bulk-forming laxatives (such as ispaghula husk) or osmotic laxatives (such as lactulose). However, these should not be used for more than a week without medical advice.

It is important to review all medications with your healthcare provider, as constipation may result from other drugs you are taking rather than tadalafil itself. Common culprits include opioid painkillers, certain antidepressants, antihistamines, and iron supplements.

When to Seek Medical Advice About Tadalafil Side Effects

While most side effects of tadalafil are mild and self-limiting, certain symptoms require prompt medical attention. Understanding when to contact your GP or seek emergency care is essential for patient safety.

Seek immediate medical attention (call 999 or go to A&E) if you experience:

• Chest pain or pressure – particularly if it occurs during or after sexual activity, as this may indicate cardiovascular problems. Importantly, do not take nitrates (such as GTN spray or tablets) for chest pain within at least 48 hours of taking tadalafil, and inform emergency services that you have recently taken tadalafil

• Sudden vision loss or changes – including blurred vision or loss of vision in one or both eyes, which may signal non-arteritic anterior ischaemic optic neuropathy (NAION)

• Sudden hearing loss or ringing in the ears – a rare but serious adverse effect

• Priapism – a painful erection lasting more than 4 hours, which requires emergency treatment to prevent permanent damage

• Severe allergic reaction – symptoms include difficulty breathing, swelling of the face, lips, tongue or throat, or severe skin rash

Contact your GP or pharmacist if:

• Digestive symptoms including constipation persist for more than 1 week despite lifestyle modifications

• You experience severe or persistent abdominal pain, especially if accompanied by vomiting

• You notice rectal bleeding, black stools, unintentional weight loss, or a new persistent change in bowel habit

• Side effects are significantly affecting your quality of life or ability to continue treatment

• You develop new symptoms after starting tadalafil that concern you

• You are taking other medications and are unsure about potential interactions

According to NICE Clinical Knowledge Summaries for erectile dysfunction, patients should have cardiovascular risk assessed before starting PDE5 inhibitors. If you have underlying heart conditions, diabetes, or other chronic illnesses, regular monitoring is important.

Your healthcare provider may adjust your tadalafil dose, suggest an alternative PDE5 inhibitor, or investigate other causes for your symptoms. Never stop taking prescribed medication without consulting your doctor first. The Yellow Card Scheme (yellowcard.mhra.gov.uk), operated by the MHRA, allows patients and healthcare professionals to report suspected side effects, contributing to ongoing medication safety monitoring in the UK.

Frequently Asked Questions