Sildenafil — evidence‑based review (for educational purposes only, not medical advice)

Sildenafil is a prescription medicine best known under the brand name Viagra. It is mainly used for erectile dysfunction (ED) and for a type of high blood pressure affecting the lungs (pulmonary arterial hypertension, PAH). This review summarizes what high‑quality evidence shows, where uncertainty remains, and what practical steps to consider if you are discussing sildenafil with a healthcare professional.

Quick summary

• What it does: Improves blood flow by enhancing nitric oxide signaling.
• Main uses: Erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).
• Effectiveness: Strong evidence for ED; moderate to strong evidence for PAH symptom improvement.
• Onset: For ED, usually works within 30–60 minutes (sexual stimulation is still required).
• Key safety issue: Must not be combined with nitrates due to risk of severe low blood pressure.

What is known

1. Mechanism of action (how it works)

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor. In simple terms, it helps maintain levels of a molecule (cGMP) that relaxes smooth muscle in blood vessel walls. This relaxation increases blood flow. In the penis, this supports erection when a person is sexually stimulated. In the lungs, it relaxes pulmonary blood vessels, lowering pressure.

2. Erectile dysfunction (ED)

Evidence strength: high. Multiple randomized controlled trials and long‑term follow‑up studies show sildenafil significantly improves erectile function compared with placebo. Benefits are seen across many causes of ED, including diabetes, post‑prostate surgery, and psychological factors.

Clinical guidelines from organizations such as the American Urological Association (AUA) and European Association of Urology (EAU) recommend PDE5 inhibitors (including sildenafil) as first‑line therapy for ED in most men, unless contraindicated.

Response rates in trials commonly range from about 60–80%, depending on the population studied. Effectiveness may be lower in severe nerve damage (for example, after radical prostatectomy).

3. Pulmonary arterial hypertension (PAH)

Evidence strength: moderate to high. Sildenafil improves exercise capacity (for example, 6‑minute walk distance), functional class, and some hemodynamic measures in PAH. It is included in major cardiology and pulmonary hypertension guidelines as one of several approved treatment options.

It does not cure PAH but can improve symptoms and slow clinical worsening in certain patients.

4. Safety profile

Common side effects include:

• Headache
• Facial flushing
• Indigestion
• Nasal congestion
• Visual changes (blue‑tinged vision, light sensitivity)

Serious but rare risks include:

• Severe low blood pressure (especially with nitrates)
• Priapism (painful erection lasting more than 4 hours)
• Sudden hearing loss (very rare)
• Non‑arteritic anterior ischemic optic neuropathy (very rare)

The most critical interaction is with nitrates (for example, nitroglycerin) or certain nitric oxide donors. The combination can cause a dangerous drop in blood pressure.

5. Typical dosing (official sources)

For erectile dysfunction, typical dosing information can be found in official prescribing information such as the U.S. FDA label:
FDA Viagra (sildenafil) prescribing information.

For pulmonary arterial hypertension, see the FDA label for Revatio (sildenafil for PAH):
FDA Revatio prescribing information.

This article does not provide personal dosing advice. Dosing depends on medical history, other medications, age, and liver or kidney function.

What is unclear / where evidence is limited

1. Long‑term outcomes beyond symptom relief

For ED, sildenafil improves erections, but it does not directly treat underlying cardiovascular disease. Whether long‑term use changes cardiovascular outcomes remains unclear.

2. Use in women

Evidence for sildenafil in female sexual arousal disorder is mixed and generally insufficient for routine use. It is not widely recommended in guidelines for this purpose.

3. Recreational use

There is limited high‑quality evidence on long‑term safety in healthy individuals using sildenafil recreationally. Psychological dependence (believing one “needs” it) is a reported concern but not well studied.

4. Off‑label uses

Sildenafil has been studied for conditions like Raynaud’s phenomenon and high‑altitude pulmonary edema. Some evidence supports benefit, but data are less robust than for ED and PAH.

Overview of approaches

For erectile dysfunction

• PDE5 inhibitors (sildenafil, tadalafil, vardenafil, avanafil)
• Lifestyle changes (weight loss, exercise, smoking cessation)
• Psychological therapy when stress or anxiety is a factor
• Vacuum erection devices
• Penile injections or implants (in selected cases)

Sildenafil is often considered a first‑line option because of strong evidence and ease of use.

For pulmonary arterial hypertension

• PDE5 inhibitors (including sildenafil)
• Endothelin receptor antagonists
• Prostacyclin analogues
• Soluble guanylate cyclase stimulators

PAH treatment is typically managed by specialists, and therapy may involve combination regimens.

General cardiovascular health

Since ED can be an early marker of cardiovascular disease, clinicians often assess blood pressure, cholesterol, blood sugar, and lifestyle factors. Addressing these may improve both heart health and erectile function.

Evidence summary table

Statement	Confidence level	Why
Sildenafil improves erectile function in most men with ED.	High	Supported by multiple randomized trials and international guidelines.
Sildenafil improves exercise capacity in PAH.	High	Backed by clinical trials and guideline recommendations.
Sildenafil reduces long‑term cardiovascular mortality in ED.	Low	No definitive long‑term mortality trials.
Recreational use is risk‑free in healthy individuals.	Low	Limited long‑term safety data outside medical indications.
Combining sildenafil with nitrates is dangerous.	High	Clear pharmacologic interaction and documented severe hypotension risk.

Practical recommendations

General safety measures

• Never combine sildenafil with nitrates unless explicitly cleared by a doctor.
• Inform your clinician about all medications and supplements.
• Seek urgent care for chest pain after taking sildenafil.
• Seek emergency care for an erection lasting more than 4 hours.

When to see a doctor

• ED that is new, worsening, or associated with chest pain or shortness of breath.
• Symptoms of PAH such as unexplained breathlessness or fatigue.
• Side effects like severe vision or hearing changes.

How to prepare for a consultation

• List current medications (especially heart drugs).
• Note medical conditions (heart disease, diabetes, high blood pressure).
• Describe how often symptoms occur and what makes them better or worse.

For broader health context, you may also be interested in our articles on cardiovascular risk factors explained, understanding blood pressure numbers, and lifestyle strategies for better vascular health. If you are comparing medical information quality online, see our guide to how to evaluate health claims.

Sources

• U.S. Food and Drug Administration (FDA). Viagra (sildenafil) Prescribing Information.
• U.S. Food and Drug Administration (FDA). Revatio (sildenafil) Prescribing Information.
• American Urological Association (AUA). Erectile Dysfunction Guideline.
• European Association of Urology (EAU). Guidelines on Sexual and Reproductive Health.
• European Society of Cardiology (ESC) / European Respiratory Society (ERS). Guidelines for Pulmonary Hypertension.
• National Health Service (NHS). Sildenafil overview.

This article is for educational purposes only and does not replace professional medical advice. Always consult a qualified healthcare provider regarding diagnosis or treatment decisions.