What Is Viagra? Uses, Dosage, and What You Need to Know in 2026

Viagra is one of the most recognized medications on the planet. Since its FDA approval in 1998, it has helped millions of men manage erectile dysfunction. But many patients — and even some who've been taking it for years — have questions about what it actually does, how to take it correctly, and what options are available. Here's everything you need to know, updated for 2026.

What Is Viagra?

Viagra is the brand name for sildenafil citrate, a medication in the class called phosphodiesterase type 5 (PDE5) inhibitors. It was originally developed by Pfizer (now Viatris) and received FDA approval for erectile dysfunction on March 27, 1998 — making it the first oral therapy approved for ED in the United States.

Generic sildenafil — which contains the identical active ingredient — became available in the US after Pfizer's patent expired. It now represents the vast majority of sildenafil prescriptions filled. The same active ingredient (sildenafil) is also marketed under the brand name Revatio for the treatment of pulmonary arterial hypertension (PAH).

What Does Viagra Treat?

Viagra (sildenafil) has two FDA-approved indications:

• Erectile dysfunction (ED): Approved as Viagra. Used as needed in men who have difficulty achieving or maintaining an erection. ED affects more than 30 million American men and has many potential causes including diabetes, cardiovascular disease, hormonal imbalances, psychological factors, and medication side effects.
• Pulmonary arterial hypertension (PAH): Approved as Revatio. Used to improve exercise tolerance in adults and children over 1 year with PAH — a serious condition involving high blood pressure in the blood vessels leading to the lungs.

An important clarification: Viagra treats ED but does not cure it. It doesn't increase sexual desire, and it won't cause an erection without sexual stimulation. It simply makes it easier to achieve and maintain an erection when you're sexually aroused.

Viagra Dosage: How Much Should You Take?

Viagra is available in three tablet strengths for erectile dysfunction:

• 25 mg: Starting dose for older patients (65+), those with liver or kidney impairment, or patients on certain medications that increase sildenafil levels
• 50 mg: Standard recommended starting dose for most patients
• 100 mg: Maximum dose; used when 50 mg provides insufficient response

How to Take Viagra Correctly

For best results, follow these guidelines:

• Take approximately 1 hour before sexual activity; effective anywhere from 30 minutes to 4 hours before
• Do not take more than once per 24-hour period
• Can be taken with or without food; however, a high-fat meal can slow absorption and delay onset
• Sexual stimulation is still required — Viagra does not cause erections without arousal
• Avoid grapefruit juice, which may increase sildenafil blood levels
• Limit alcohol, which can worsen dizziness and low blood pressure

Who Should NOT Take Viagra?

Viagra is contraindicated in patients who:

• Take nitrate medications in any form (nitroglycerin, isosorbide, "poppers") — potentially fatal blood pressure drop
• Take GC stimulators such as riociguat (Adempas)
• Have a known allergy to sildenafil or any component of the tablet
• Have pulmonary veno-occlusive disease

How Effective Is Viagra?

Clinical trials have demonstrated that Viagra significantly improves erectile function in men with ED. In studies, most men achieved an erection within an hour of taking the pill. However, response rates vary depending on the underlying cause of ED — men with psychogenic ED tend to respond better than those with vascular or neurogenic causes.

For men who don't respond to the initial dose, increasing to 100 mg (if tolerated) or switching to a different PDE5 inhibitor (such as tadalafil) may improve results.

For a deeper explanation of how sildenafil works in the body, see: How Does Viagra Work? Mechanism of Action Explained.