Does sildenafil cause constipation? This is a question some patients ask when experiencing digestive changes whilst taking this medication. Sildenafil, widely known as Viagra, is a phosphodiesterase type 5 (PDE5) inhibitor prescribed for erectile dysfunction and pulmonary arterial hypertension. Constipation is not listed among the recognised common side effects in UK prescribing information from the MHRA or manufacturer's guidance. This article examines the evidence, explores why digestive symptoms may occur, and provides practical advice on managing bowel health whilst taking sildenafil.

Does Sildenafil Cause Constipation?

Sildenafil, commonly known by the brand name Viagra, is a phosphodiesterase type 5 (PDE5) inhibitor primarily prescribed for erectile dysfunction and, in different dosing regimens, for pulmonary arterial hypertension. Constipation is not listed among the common or well-documented side effects of sildenafil in official prescribing information from the MHRA or in the manufacturer's Summary of Product Characteristics (SmPC).

There is no established direct pharmacological mechanism by which sildenafil would cause constipation. The drug works by inhibiting PDE5 enzymes, which leads to increased cyclic guanosine monophosphate (cGMP) levels in smooth muscle tissue, primarily affecting vascular smooth muscle in the corpus cavernosum and pulmonary vasculature. This mechanism does not directly target gastrointestinal motility or function.

While constipation is not typically reported, other gastrointestinal effects such as dyspepsia (indigestion) and nausea are recognised common side effects of sildenafil. Individual responses to medications can vary considerably. Some patients may experience changes in bowel habits for reasons that are multifactorial, including dietary changes, hydration status, anxiety related to sexual performance, or coincidental factors unrelated to the medication itself.

If you are experiencing constipation whilst taking sildenafil, it is advisable to consider other potential contributing factors, such as other medications (calcium-channel blockers, opioids, iron supplements, antimuscarinic drugs) or underlying conditions. Discuss your symptoms with your GP or prescribing clinician, who can help determine whether the symptom is related to sildenafil or another cause, and provide appropriate guidance on management.

Common Side Effects of Sildenafil

Sildenafil is generally well tolerated, but like all medications, it can cause side effects in some individuals. The most frequently reported adverse effects are related to its vasodilatory properties—the widening of blood vessels that occurs as part of its therapeutic mechanism.

Common side effects include:

• Headaches – very common (affecting more than 1 in 10 people)

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

• Dyspepsia (indigestion) – common

• Nasal congestion – common

• Nausea – common

• Visual disturbances – including altered colour perception (particularly a blue tinge), increased light sensitivity, or blurred vision

• Dizziness – which may relate to blood pressure changes

These effects typically occur within a few hours of taking the medication and resolve as the drug is metabolised and eliminated from the body. Sildenafil has a half-life of approximately 3–5 hours, meaning most side effects are transient.

Less common but more serious adverse effects can include sudden vision loss, sudden hearing loss, priapism (a prolonged and painful erection lasting more than four hours), and cardiovascular events in susceptible individuals.

Important safety information:

• Sildenafil must not be used with nitrate medications (including GTN spray/tablets, isosorbide mononitrate/dinitrate, and nicorandil) or recreational 'poppers' (amyl nitrite) as this can cause a dangerous drop in blood pressure

• It must not be used with riociguat (used for pulmonary hypertension)

• Caution is needed when taking sildenafil with alpha-blocker medications due to potential hypotension

• Certain medications (including some antibiotics, antifungals, and HIV medications) can increase sildenafil levels in the blood through CYP3A4 enzyme inhibition

Gastrointestinal symptoms beyond dyspepsia and nausea—such as constipation—are not prominently featured in the adverse effect profile, although diarrhoea is reported as an uncommon side effect (affecting up to 1 in 100 people).

Why Digestive Symptoms May Occur with Sildenafil

Although constipation is not a recognised common side effect of sildenafil, there are several plausible explanations for why some individuals might experience digestive symptoms whilst taking this medication.

Indirect pharmacological effects: Sildenafil's vasodilatory action primarily targets vascular smooth muscle, but PDE5 enzymes are present in various tissues throughout the body. While there is limited evidence linking sildenafil directly to constipation, individual variations in enzyme distribution or sensitivity could theoretically contribute to subtle effects on gastrointestinal function in some people.

Lifestyle and behavioural factors: Patients taking sildenafil may inadvertently alter their dietary habits, fluid intake, or meal timing around sexual activity. Dehydration, reduced fibre intake, or changes in eating patterns can all contribute to constipation. Additionally, anxiety or stress related to sexual performance—factors that may have prompted sildenafil use in the first place—can affect digestive function through the gut-brain axis.

Concurrent medications: Many patients taking sildenafil are older adults who may be on multiple medications for conditions such as hypertension, diabetes, or cardiovascular disease. Certain medications commonly used in these populations are well-known causes of constipation, including:

• Calcium-channel blockers

• Opioid analgesics

• Iron supplements

• Antimuscarinic drugs

• Tricyclic antidepressants

• Some antihypertensives

The temporal association with starting sildenafil may be coincidental rather than causal.

Underlying health conditions: Conditions such as diabetes, which is prevalent among men with erectile dysfunction, can cause autonomic neuropathy affecting gastrointestinal motility. Hypothyroidism, Parkinson's disease, and age-related changes in bowel function are also common and may coincide with the period when sildenafil is prescribed.

If digestive symptoms develop or worsen after starting sildenafil, a thorough review of all potential contributing factors is warranted before attributing the symptom solely to the medication.

When to Seek Medical Advice About Side Effects

Whilst most side effects of sildenafil are mild and self-limiting, certain symptoms warrant 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:

• Priapism – an erection lasting longer than four hours, which requires urgent treatment to prevent permanent damage

• Sudden vision loss in one or both eyes, which may indicate non-arteritic anterior ischaemic optic neuropathy (NAION)

• Sudden hearing loss or decrease in hearing, sometimes accompanied by tinnitus or dizziness

• Chest pain or discomfort during or after sexual activity – IMPORTANT: if chest pain occurs after taking sildenafil, do NOT take nitrate medications (such as GTN spray/tablets) as this combination can cause a dangerous drop in blood pressure

• Severe allergic reactions including difficulty breathing, swelling of the face, lips, tongue, or throat, or severe skin reactions

Contact your GP or prescribing clinician within a few days if:

• Side effects such as headaches, flushing, or indigestion are persistent, severe, or significantly affecting your quality of life

• You develop new or worsening digestive symptoms, including persistent constipation, that concern you

• You experience dizziness or light-headedness that interferes with daily activities

• Visual disturbances persist beyond the expected duration of drug action

• You have questions about interactions with other medications or supplements

For non-emergency concerns outside of GP hours, NHS 111 can provide advice on whether and how urgently you need medical help.

Regarding constipation specifically, if this symptom is severe, persistent beyond a week, accompanied by abdominal pain, rectal bleeding, unexplained weight loss, or represents a significant change from your normal bowel pattern, medical evaluation is appropriate. Your clinician can assess whether the symptom is medication-related or requires investigation for other causes.

You can report suspected side effects to the MHRA through the Yellow Card scheme (yellowcard.mhra.gov.uk), which helps monitor medication safety.

Managing Digestive Health While Taking Sildenafil

If you experience constipation or other digestive symptoms whilst taking sildenafil, several practical strategies can help maintain bowel health without necessarily discontinuing the medication.

Dietary modifications:

• Increase dietary fibre intake gradually to 25–30 grams daily through wholegrain cereals, fruits, vegetables, pulses, and legumes

• Ensure adequate fluid intake—aim for 6–8 glasses (approximately 1.5–2 litres) of water daily, unless you have heart failure or kidney disease (in which case, seek advice from your healthcare professional before increasing fluids)

• Consider natural laxative foods such as prunes, figs, or kiwi fruit

• Limit foods that may worsen constipation, including processed foods, excessive dairy, and refined carbohydrates

Lifestyle measures:

• Engage in regular physical activity, which stimulates intestinal motility—aim for at least 150 minutes of moderate-intensity exercise weekly as per NHS recommendations

• Establish a regular bowel routine, allowing adequate time and privacy

• Respond promptly to the urge to defecate rather than delaying

• Review your medication list with your GP to identify any other potential contributors to constipation

When lifestyle measures are insufficient:

If constipation persists despite dietary and lifestyle modifications for more than a week, speak with your GP about appropriate laxative options. According to NICE guidance and the BNF, treatment options include:

• Osmotic laxatives (such as macrogol) – often considered first-line for persistent constipation

• Bulk-forming laxatives (such as ispaghula husk) – suitable if dietary fibre is low and fluid intake is adequate

• Stimulant laxatives (such as senna or bisacodyl) – may be used for short-term relief but are not recommended for prolonged use without medical supervision

Medication review:

Your clinician may consider whether sildenafil is the optimal treatment for your condition or whether alternative PDE5 inhibitors (such as tadalafil or vardenafil) might be better tolerated. However, given that constipation is not a recognised class effect of PDE5 inhibitors, switching medications may not resolve the symptom if other factors are responsible.

Maintaining open communication with your healthcare team ensures that both your primary condition and any side effects are managed effectively, optimising your overall treatment outcome and quality of life.

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