Viagra contains one active ingredient: sildenafil citrate. Each tablet also includes nine inactive ingredients that hold the pill together, help it dissolve, and give it its distinctive blue color. The tablets come in three strengths (25 mg, 50 mg, and 100 mg), all shaped as the recognizable blue, film-coated, rounded diamond.
The Active Ingredient: Sildenafil Citrate
Sildenafil citrate is the compound that actually treats erectile dysfunction. It was approved by the FDA in March 1998 as the first oral treatment for ED, and it works by blocking a specific enzyme in blood vessel walls called PDE5.
Here’s the short version of how it works: when you’re sexually aroused, your body releases nitric oxide in the tissue of the penis. That nitric oxide triggers production of a chemical messenger called cGMP, which relaxes smooth muscle in blood vessel walls and allows blood flow to increase. Normally, PDE5 breaks down cGMP fairly quickly. Sildenafil blocks PDE5 from doing its job, so cGMP accumulates and the blood vessels stay relaxed longer, producing a stronger and more sustained erection.
One important detail: sildenafil only works when sexual arousal is already happening. Without that initial release of nitric oxide, there’s no cGMP for the drug to protect. It amplifies a natural process rather than creating one from scratch.
Inactive Ingredients in the Tablet
Beyond sildenafil citrate, each Viagra tablet contains:
- Microcrystalline cellulose and anhydrous dibasic calcium phosphate: bulk fillers that give the tablet its size and shape
- Croscarmellose sodium: helps the tablet break apart and dissolve in your stomach
- Magnesium stearate: a lubricant that prevents the powder from sticking to manufacturing equipment
- Hypromellose, titanium dioxide, and triacetin: form the smooth film coating on the outside of the tablet
- FD&C Blue #2 aluminum lake: the dye responsible for Viagra’s signature blue color
- Lactose: a sugar used as a filler and binder
The presence of lactose is worth noting if you have a severe lactose intolerance or allergy. The amount in a single tablet is small, but it’s there. None of the inactive ingredients contain gluten.
How It Behaves in Your Body
Viagra is typically taken about one hour before sexual activity. Effects can begin within 30 minutes and last up to four hours, though the strongest response tends to occur around the two-hour mark. After that, the effect gradually diminishes.
Food can affect how quickly the drug kicks in. A high-fat meal slows absorption, which may delay the onset. Taking it on an empty or light stomach generally produces faster results.
Why Nitrates Are Dangerous With Viagra
Sildenafil amplifies the same signaling pathway that nitroglycerin and other nitrate medications use to lower blood pressure. Nitrates flood the body with nitric oxide, which ramps up cGMP production. If sildenafil is simultaneously preventing cGMP from being broken down, the combined effect can cause a severe, potentially life-threatening drop in blood pressure. This is why sildenafil is never taken alongside nitrate medications in any form, whether they’re prescribed for chest pain, taken as a daily heart medication, or used recreationally (like amyl nitrite poppers).
Generic Sildenafil vs. Brand-Name Viagra
Generic versions of Viagra contain the same active ingredient, sildenafil citrate, at the same strength. The FDA requires generics to be chemically identical in terms of the active compound, dosage, safety, and effectiveness. The tablets may look different in shape, color, or size because generic manufacturers use their own inactive ingredient formulations. If you have sensitivities to specific dyes or fillers, check the inactive ingredient list on your particular generic, since it won’t necessarily match the brand-name version.
The three available strengths (25 mg, 50 mg, and 100 mg) are the same across brand and generic. Most people start at 50 mg, with adjustments made based on how well it works and whether side effects occur.