Sildenafil: what it is, how it works, and what to consider before use
Disclaimer: This article is for educational purposes only and does not replace consultation with a qualified healthcare professional. Sildenafil is a prescription medication in many countries. Do not start, stop, or change the dose without medical advice.
Key terms (glossary)
- Sildenafil
- An active pharmaceutical ingredient used primarily to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).
- Erectile dysfunction (ED)
- The persistent inability to achieve or maintain an erection sufficient for satisfactory sexual activity.
- PDE5 inhibitor
- A class of drugs (including sildenafil) that block the enzyme phosphodiesterase type 5 to enhance blood flow.
- cGMP (cyclic guanosine monophosphate)
- A signaling molecule that relaxes smooth muscle and increases blood flow in the penis.
- Nitric oxide (NO)
- A natural chemical released during sexual stimulation that triggers cGMP production.
- Vasodilation
- Widening of blood vessels, leading to increased blood flow.
- Onset of action
- The time it takes for sildenafil to start working (usually 30–60 minutes).
- Duration of action
- The period during which the drug remains effective (about 4 hours for ED).
- Nitrates
- Medications used for chest pain (e.g., nitroglycerin) that can dangerously interact with sildenafil.
- Hypotension
- Low blood pressure, a potential side effect or interaction risk.
- Priapism
- A prolonged and painful erection lasting more than 4 hours; a medical emergency.
- Pulmonary arterial hypertension (PAH)
- A condition involving high blood pressure in the arteries of the lungs; treated with lower-dose sildenafil.
- Contraindications
- Conditions or factors that make the use of a drug unsafe.
- Generic medication
- A drug with the same active ingredient as a brand-name product but typically at lower cost.
Clear explanation
1. Why sildenafil is prescribed (causes and indications)
Sildenafil is most commonly prescribed for erectile dysfunction, which may result from vascular disease, diabetes, hormonal imbalance, neurological disorders, psychological factors, or medication side effects. Because erection depends on adequate blood flow, conditions affecting blood vessels are a frequent cause.
In lower doses and under specific protocols, sildenafil is also used to treat pulmonary arterial hypertension, where it helps relax blood vessels in the lungs and improve exercise capacity.
2. How sildenafil works (mechanism of action)
Sildenafil belongs to the class of PDE5 inhibitors. During sexual stimulation, nitric oxide (NO) is released in penile tissue. This stimulates production of cGMP, which relaxes smooth muscle and allows increased blood flow.
The enzyme PDE5 normally breaks down cGMP. By blocking PDE5, sildenafil increases and prolongs cGMP activity, enhancing natural erectile response. Importantly, sexual stimulation is still required—the drug does not cause automatic erection.
3. Manifestations and expected effects
When taken for ED, sildenafil may:
- Improve ability to achieve an erection
- Improve ability to maintain erection
- Increase confidence related to sexual performance
Common side effects can include headache, facial flushing, nasal congestion, indigestion, and temporary visual changes (such as blue-tinged vision). Most are mild and dose-dependent.
4. Diagnosis before starting treatment
Before prescribing sildenafil, a healthcare professional may:
- Review cardiovascular history
- Assess current medications (especially nitrates or alpha-blockers)
- Evaluate risk factors such as diabetes or hypertension
- Consider psychological contributors
In some cases, additional testing (e.g., blood glucose, testosterone levels, lipid profile) may be recommended.
5. Treatment approaches and dosing principles
For erectile dysfunction, sildenafil is typically taken 30–60 minutes before sexual activity. It should not usually be taken more than once per day. The starting dose often depends on age, liver or kidney function, and concurrent medications.
For broader context about men’s health and medication safety, see our overview in Men’s Health Basics and guidance on Safe Use of Prescription Drugs. International readers may consult localized guidance in our European Health Resources section.
Reader checklist
What you can do
- Consult a healthcare professional before first use
- Inform your doctor about all medications and supplements
- Take sildenafil exactly as prescribed
- Allow sufficient time (30–60 minutes) before sexual activity
- Adopt heart-healthy habits (exercise, balanced diet, smoking cessation)
What to avoid
- Do not combine with nitrates (nitroglycerin, isosorbide)
- Avoid excessive alcohol intake before use
- Do not exceed recommended dose
- Do not use recreational “street” versions of sildenafil
- Avoid combining with other PDE5 inhibitors unless instructed
When to see a doctor urgently (red flags)
- Chest pain during or after sexual activity
- Erection lasting more than 4 hours (possible priapism)
- Sudden loss of vision or hearing
- Severe dizziness or fainting
- Allergic reactions (swelling, difficulty breathing)
Key terms explained simply
| Term | In simple words | Why it matters |
|---|---|---|
| PDE5 inhibitor | A drug that helps blood vessels relax | Explains how sildenafil improves erections |
| cGMP | A molecule that increases blood flow | Central to the erection process |
| Nitrates | Heart medications for chest pain | Dangerous interaction with sildenafil |
| Priapism | A prolonged painful erection | Requires emergency care |
| Hypotension | Low blood pressure | Can occur with drug interactions |
Specialist comment (generalized)
Sildenafil is generally effective and well studied for erectile dysfunction, but its safety depends heavily on proper patient selection. Cardiovascular risk assessment and medication review are essential before prescribing. Patients should be clearly informed about potential interactions and warning signs that require urgent care.
Sources
- U.S. Food and Drug Administration (FDA). Viagra (sildenafil) prescribing information.
- European Medicines Agency (EMA). Sildenafil-containing medicinal products: EPAR summaries.
- American Urological Association (AUA). Guideline on the Management of Erectile Dysfunction.
- Mayo Clinic. Sildenafil (oral route) – drug information and precautions.
If specific dosage numbers or country-specific regulatory details are required, consult the official prescribing information for your region, as recommendations may vary.