Sildenafil is a well-known medication prescribed for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). Marketed under brand names like Viagra, Revatio, and Liqrev, this medicine belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors.
In this guide, we’ll cover its uses, mechanism of action, dosage forms, side effects, precautions, and FAQs.
What is Sildenafil Used For?
Sildenafil is commonly prescribed for several distinct medical uses. Below are the primary, evidence-based indications and a short note on off-label use:
1. Erectile Dysfunction (ED) — Primary use for Viagra:
Sildenafil helps men who have trouble getting or keeping an erection adequate for sexual activity. It does not increase sexual desire; sexual stimulation is still required for the drug to work. Typical dosing guidance for ED (timing and frequency) is described in product labelling and clinical guidance. FDA Access DataMayo Clinic
2. Pulmonary Arterial Hypertension (PAH) — Revatio / Liqrev formulations:
For PAH, sildenafil relaxes the pulmonary blood vessels, lowering pulmonary arterial pressure and improving exercise ability and symptoms. Revatio is an FDA-approved treatment for WHO Group I PAH in adults (and in some pediatric patients), and it’s usually given on a regular schedule (e.g., three times daily) rather than “as needed.” FDA Access Data+1
3. Other (off-label) uses:
Clinicians sometimes prescribe sildenafil for conditions not listed on the label when evidence or clinical judgment supports it — examples reported in the literature include certain pediatric pulmonary vascular disorders, altitude-related hypoxemia, or experimental/ compassionate uses. Off-label use should always be guided by a specialist and individualized risk–benefit assessment. NCBIPMC
How Does Sildenafil Work (Mechanism of Action)?
Sildenafil belongs to a group of medicines called phosphodiesterase type 5 (PDE5) inhibitors. Its main action is to block the PDE5 enzyme, which plays a role in regulating blood flow in certain parts of the body.
By inhibiting this enzyme, sildenafil allows blood vessels to relax and widen, improving circulation where it is needed most.
The way it works depends on the condition being treated:
1. For Erectile Dysfunction (ED)
- Enhances blood circulation to the penis: During sexual stimulation, sildenafil increases levels of cyclic guanosine monophosphate (cGMP), a chemical that relaxes smooth muscle and boosts blood flow.
- Relaxes smooth muscles and widens blood vessels: This relaxation makes it easier for the penile blood vessels to fill with blood.
- Helps achieve stronger and longer-lasting erections: The result is an erection firm enough for satisfactory sexual activity. Importantly, sildenafil only works when sexual stimulation is present—it does not automatically cause an erection.
2. For Pulmonary Arterial Hypertension (PAH)
- Relaxes the pulmonary blood vessels: In PAH, blood vessels in the lungs are narrowed and stiff. Sildenafil helps these vessels dilate.
- Lowers lung blood pressure: By reducing vascular resistance in the pulmonary arteries, the heart can pump blood more easily through the lungs.
- Reduces strain on the heart and improves exercise tolerance: Patients often notice better breathing, less fatigue, and improved capacity for daily activities or physical exertion.
How is Sildenafil Supplied (Dosage Forms & Brands)?
Brands and Names:
- Viagra (commonly for ED)
- Revatio (for PAH)
- Liqrev (oral suspension for PAH)
Available Dosage Forms and Strengths:
- Tablets: 25 mg, 50 mg, 100 mg (Viagra for ED)
- Tablets/Suspension: 20 mg (Revatio, Liqrev for PAH)
- Liquid Suspension: Measured with an oral syringe for accurate dosing.
How Should Sildenafil Be Taken?
For Erectile Dysfunction:
- Take 30 minutes to 4 hours before sexual activity (best around 1 hour before).
- Do not exceed 1 dose in 24 hours.
- Works best on an empty stomach (a high-fat meal may delay effect).
- For PAH (Revatio/Liqrev):
- Usually prescribed 3 times daily.
- Take at evenly spaced times, with or without food.
Always follow your doctor’s dosage instructions.
Possible Side Effects of Sildenafil
Common Side Effects
These are usually mild and may improve as your body adjusts to the medication:
- Headache – the most frequently reported side effect.
- Flushing (warmth, redness, or hot feeling in the face, neck, or chest).
- Indigestion or heartburn.
- Stuffy or runny nose.
- Dizziness or lightheadedness, especially when standing up quickly.
- Muscle aches or back pain.
- Vision changes, such as blurred vision, light sensitivity, or a temporary blue/green color tint.
Serious Side Effects (Seek Medical Help Immediately)
Although rare, some people may experience more serious reactions. Stop using sildenafil and get medical help if you notice:
- Sudden vision loss or severe changes in eyesight.
- Sudden hearing loss, sometimes with ringing in the ears or dizziness.
- Chest pain, irregular heartbeat, or fainting.
- Shortness of breath or difficulty breathing.
- A painful or prolonged erection lasting more than 4 hours (priapism), which can cause permanent damage if untreated.
- Severe allergic reactions, including swelling of the lips, tongue, throat, or face, rash, or difficulty swallowing/breathing.
Precautions & Warnings
Before using sildenafil, tell your doctor if you:
- Take nitrate medications (dangerous interaction causing severe low blood pressure).
- Use street drugs (“poppers”) containing nitrates.
- Have heart problems, recent surgery, or history of stroke.
- Have liver/kidney disease, blood cell disorders, or eye conditions.
- Are pregnant, breastfeeding, or taking medications that may interact.
Key Points to Remember
- Sildenafil treats symptoms, but does not cure ED or PAH.
- It does not increase sexual desire. Sexual stimulation is still required.
- Not a protection against HIV or STDs.
- Should be used strictly under medical supervision.
Conclusion
Frequently Asked Questions (FAQs) About Sildenafil
What is sildenafil used for?
How long does sildenafil take to work?
How long do the effects of sildenafil last?
Can I take sildenafil every day?
- For ED: Sildenafil is usually taken only when needed, not more than once in 24 hours.
- For PAH: Doctors may prescribe it 3 times daily as ongoing treatment. Always follow your healthcare provider’s advice.
Who should not take sildenafil?
Does sildenafil increase sexual desire?
What are the common side effects of sildenafil?
What are the serious side effects of sildenafil?
Can women take sildenafil?
What should I avoid while taking sildenafil?
Avoid:
- Nitrates or “poppers” (dangerous interaction).
- Excess alcohol (may worsen side effects).
- Grapefruit or grapefruit juice (can interfere with drug metabolism).
- High-fat meals right before taking it (can delay effectiveness).
