Short answer: Sildenafil is a PDE5 inhibitor that dilates blood vessels and temporarily improves blood flow, which can support an erection during sexual arousal. Common side effects include headache, flushing, and a stuffy nose. The medication requires a prescription.
This page covers the mechanism of action and side effects of sildenafil, the active ingredient behind well-known erectile dysfunction drugs. If you are looking for information about prescription requirements, purchasing, and alternatives, please read our page about sildenafil and prescription requirements. Here, we focus on the mechanism and what you can expect.
What is sildenafil?
Sildenafil belongs to the PDE5 inhibitors, a group of substances that act on blood vessels. It is a medication prescribed for erectile problems. The substance is found in Viagra and generic variants.
How does sildenafil work?
During sexual arousal, the body produces nitric oxide, which triggers a chain of reactions that relax the blood vessels in the genital area and increase blood flow. An enzyme called PDE5 normally breaks down this process. Sildenafil inhibits this enzyme, allowing the increased blood flow to be maintained longer.
Important: sildenafil only works during sexual arousal. Without arousal, nothing happens. The medication does not create desire and does not work on its own; it supports a natural process.
Common side effects
Like any medication, sildenafil can cause side effects. Most are mild and temporary. Commonly reported side effects include:
- Headache
- Flushing (a warm, red feeling in the face)
- A stuffy or runny nose
- Mild digestive disturbances or stomach discomfort
- Dizziness or visual effects, such as a blue tint
These symptoms usually resolve on their own. If you experience discomfort or have concerns, discuss them with your doctor or pharmacist.
Rare, serious side effects
Rarely, more serious effects occur that require immediate attention. Examples include a prolonged, painful erection, sudden hearing or vision loss, or heart problems. These are uncommon, but if such symptoms appear, seek medical help immediately. Because of these risks and interactions with heart medications, sildenafil is prescription-only.
When to see a doctor?
Sildenafil should be used under medical supervision. If you use it and experience bothersome or unusual symptoms, contact your doctor or pharmacist. For serious symptoms such as a persistent erection or sudden hearing or vision loss, seek immediate medical assistance.
Frequently asked questions
How exactly does sildenafil work?
Sildenafil inhibits the enzyme PDE5, which helps maintain increased blood flow during sexual arousal longer. It only works with arousal and does not itself create desire.
What are the most common side effects of sildenafil?
Headache, flushing, a stuffy nose, mild stomach discomfort, and sometimes dizziness or visual effects. Usually mild and temporary.
Are there dangerous side effects?
Rare but possible: a prolonged painful erection, sudden hearing or vision loss, or heart problems. Immediate medical help is needed if these occur.
Sources: Pharmacotherapeutic Compass, Medicines Information Bank (CBG-MEB), package leaflet. This information does not replace medical advice. Always consult your doctor or pharmacist if you have complaints, are using medication, or have doubts.
