ED medications: Viagra vs Cialis vs Levitra

How PDE5 inhibitors work

During sexual arousal, nerves release nitric oxide in the penis, raising levels of a messenger called cGMP that relaxes smooth muscle and increases blood flow, producing an erection. An enzyme called phosphodiesterase type 5 (PDE5) breaks cGMP back down. PDE5 inhibitors — sildenafil, tadalafil and vardenafil — block that enzyme, so cGMP lasts longer and erections become easier to achieve and maintain. Crucially, they enhance the natural response to stimulation rather than creating an erection on their own — sexual arousal is still required.

Side-by-side comparison

The three medications share the same mechanism but differ in onset, duration and how food affects them. The "best" choice depends on your health, the other medicines you take, and your lifestyle — a decision best made with your physician.

Values are general approximations from prescribing information and clinical literature; individual response varies.

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What the research shows

Across hundreds of randomized controlled trials and decades of real-world use, PDE5 inhibitors are consistently effective for ED of many causes — improving the ability to achieve and maintain erections compared with placebo in the majority of men. Comparative studies generally find the three drugs broadly similar in overall effectiveness, with differences driven mostly by timing, duration and individual tolerability rather than raw efficacy. Explore each medication's dedicated page for the details.

Brand vs generic: are the cheaper versions safe?

Each of these medications is now available as an FDA-approved generic — the same active ingredient at a much lower price. Genuine generics are held to the same standards as the brand; the real danger is counterfeit product sold without a prescription. These guides explain how safe generics are, whether you should buy them, and how to verify quality.

Safety basics everyone should know

• Never combine with nitrates. Taking a PDE5 inhibitor with nitrate heart medications (or recreational "poppers") can cause a dangerous drop in blood pressure.
• Tell your doctor about all medications, especially alpha-blockers and certain other blood-pressure drugs.
• Heart health matters. Sexual activity is exertion; men with significant heart disease should be evaluated first.
• Seek urgent care for an erection lasting more than 4 hours (priapism) or sudden vision or hearing changes.
• Buy only from licensed pharmacies with a valid prescription. Counterfeit ED pills sold online are common and can be dangerous.