Sildenafil is a prescription medicine used mainly to treat erectile dysfunction (ED) in men, and also pulmonary arterial hypertension (PAH). It belongs to a group of drugs called phosphodiesterase type-5 (PDE5) inhibitors, and it is the active ingredient in Viagra. For ED, it works by increasing blood flow to the penis during sexual stimulation, helping a man get and keep an erection. It is taken as needed about an hour before sex, no more than once a day, and only under medical guidance.
Because sildenafil sits at the heart of ED treatment, understanding what it is and how it is used makes everything else easier to follow. It is a well-established medicine with a clear mechanism and clear limits — not an aphrodisiac, and not a one-size-fits-all answer.
What sildenafil treats
Sildenafil is used primarily for male sexual function problems — impotence, or ED. Under the brand name Revatio it is also used for pulmonary hypertension, a condition of high blood pressure in the vessels that supply the lungs. So the same molecule treats two very different conditions, which is why dosing and branding differ depending on the use.
| Aspect | Detail |
|---|---|
| Drug class | PDE5 inhibitor |
| Main uses | Erectile dysfunction; pulmonary hypertension (Revatio) |
| Forms | Oral tablet; liquid suspension |
| ED timing | About 1 hour before sex; effects last 2-6 hours |
| Limit | No more than once daily; prescription only |
How it works
For ED, sildenafil increases blood flow to the penis during sexual stimulation, which can produce an erection; it also helps maintain the erection after ejaculation and shortens the refractory time before a second erection. For pulmonary hypertension, the exact mechanism is less clear, but it is thought to relax the blood vessels in the lungs, improving flow and reducing pressure. In both cases the theme is the same: sildenafil relaxes blood vessels so blood moves more freely.
Forms and how it is taken
Sildenafil is available as an oral tablet — the most common form — and as a liquid suspension for people who have trouble swallowing pills. For ED it is taken as needed, most effectively about one hour before sexual activity, with effects lasting roughly two to six hours; it should not be taken more than once a day. For pulmonary hypertension it is taken on a schedule set by the doctor. Crucially, sildenafil needs sexual stimulation to work for ED — it does not create an erection on its own.
Side effects
Common side effects include headache, flushing and an upset stomach. More serious but rarer effects include sudden vision loss, hearing loss and an erection lasting longer than four hours (priapism), which needs immediate medical attention. Most men tolerate sildenafil well, but knowing these signals helps you act promptly if something goes wrong.
Interactions and precautions
Sildenafil can interact with other medicines, including nitrates, alpha-blockers and some HIV/AIDS drugs. The interaction with nitrates is the most dangerous, as it can cause a severe drop in blood pressure. Before starting, discuss your medical conditions and current medicines with your doctor so they can confirm sildenafil is safe and appropriate for you.
What sildenafil does not do
It helps to be clear about the limits, because misunderstandings here cause both disappointment and risk. Sildenafil is not an aphrodisiac: it does not create sexual desire or arousal, and it will do nothing if the interest is not already there. It does not "cure" erectile dysfunction either — it treats the symptom on demand rather than reversing the underlying cause, which might be vascular, hormonal or psychological. And it offers no protection whatsoever against sexually transmitted infections, so condoms and safe-sex practices are still essential. Finally, it is not a recreational performance booster for men without ED; taking it without need exposes you to side effects and interactions for no real benefit. Seen correctly, sildenafil is a targeted tool for a specific physical problem, most effective when the cause of the ED is also understood and addressed.
Generic vs brand
Sildenafil is available by prescription only in the US. The key difference between brand-name Viagra and generic sildenafil is price: the generic is the same active ingredient at a lower cost. In short, sildenafil is an effective treatment for ED and pulmonary hypertension that works by improving blood flow — always to be used after a conversation with a healthcare provider.
To see how it acts on the body, read does Viagra dilate or constrict blood vessels. For what it feels like, see what it feels like to take Viagra. And for using it well, read best practices for safe and effective use.
Frequently asked questions
- What is sildenafil used for?
- Mainly erectile dysfunction, and also pulmonary arterial hypertension under the brand Revatio.
- How is sildenafil taken for ED?
- As needed, about an hour before sex, no more than once a day, and only with sexual stimulation to work.
- Is sildenafil the same as Viagra?
- Essentially yes. Sildenafil is the active ingredient in Viagra; the generic is the same medicine at a lower price.
- Does it protect against STIs?
- No. Sildenafil treats erections only; safe-sex practices and condoms are still needed.
For the full picture of causes and treatments, return to the erectile dysfunction and male sexual health hub.