Viagra is a prescription medication used to treat erectile dysfunction (ED). It contains the active ingredient sildenafil citrate, which works by increasing blood flow to the penis to help achieve and maintain an erection. Originally developed by Pfizer as a treatment for chest pain and high blood pressure, sildenafil’s effect on erections was discovered as an unexpected side effect during clinical trials. The FDA approved it for ED in 1998, and it quickly became one of the most recognized medications in the world.
What the Pill Looks Like
Viagra tablets are blue, film-coated, and shaped like a rounded diamond. They come in three strengths: 25 mg, 50 mg, and 100 mg. Each tablet is stamped with “PFIZER” on one side and a code on the other that matches the strength: “VGR25,” “VGR50,” or “VGR100.” These markings help distinguish authentic tablets from counterfeits, which are common with this particular drug.
How Viagra Works in the Body
When you’re sexually aroused, your body releases a chemical messenger called cGMP that relaxes the smooth muscle in blood vessel walls, allowing blood to flow into the penis. Normally, an enzyme called PDE5 breaks down cGMP fairly quickly. Sildenafil blocks that enzyme, so cGMP stays active longer and blood vessels stay relaxed and open. The result is stronger, more sustained blood flow.
This is why Viagra doesn’t cause an automatic erection on its own. Sexual stimulation is still needed to trigger the initial release of cGMP. The pill simply keeps that natural process going longer and more effectively than it would otherwise.
How and When to Take It
The standard starting dose for most adults is 50 mg, taken about one hour before sexual activity. It can be taken anywhere from 30 minutes to 4 hours beforehand, giving a reasonable window of flexibility. For adults 65 and older, the recommended starting dose is lower, at 25 mg. The medication should not be taken more than once per day.
A heavy or high-fat meal can slow down absorption, so taking it on a relatively empty stomach tends to produce faster results. The effects typically last four to six hours, though the drug stays in your system longer than that at lower concentrations. Sildenafil also comes in an oral film form at the same dosages for people who prefer not to swallow a tablet.
Common Side Effects
Most side effects are mild and related to the same blood-vessel-relaxing action that makes the drug work. In clinical trials involving over 700 patients, the most frequently reported effects were:
- Headache: 16% of users, compared to 4% on placebo
- Flushing: 10%, versus 1% on placebo
- Indigestion: 7%, versus 2% on placebo
- Nasal congestion: 4%
- Abnormal vision: 3%, typically a mild blue-green color tinge or increased light sensitivity. This was temporary, and only one patient in the trials stopped taking the drug because of it.
- Dizziness: 2%
These effects generally fade as the drug leaves your system. Headache and flushing are the most common by a wide margin, and both stem from blood vessels dilating in areas beyond the penis.
Who Should Not Take Viagra
The most critical safety concern is combining sildenafil with nitrate medications, which are commonly prescribed for chest pain (such as nitroglycerin). Both drugs lower blood pressure through similar pathways, and taking them together can cause a dangerous, potentially life-threatening drop in blood pressure. This also applies to recreational drugs known as “poppers” (amyl nitrate or amyl nitrite), which work the same way.
Sildenafil is also contraindicated for anyone taking a type of medication called a guanylate cyclase stimulator, used for pulmonary hypertension. And anyone who has had an allergic reaction to sildenafil in any form should avoid it entirely.
Generic Sildenafil
Generic versions of Viagra are now widely available and contain the same active ingredient, sildenafil citrate. They are considered therapeutically equivalent to the brand-name version, meaning they work the same way at the same doses. The main practical difference is price: generics are significantly cheaper. The pills may look different in shape or color since generic manufacturers use their own designs, but the medication inside is identical.
Beyond Erectile Dysfunction
Sildenafil is also prescribed under the brand name Revatio for pulmonary arterial hypertension, a condition where blood pressure in the arteries of the lungs becomes dangerously high. The same mechanism that relaxes blood vessels in the penis works on blood vessels in the lungs, reducing the strain on the heart. Revatio uses lower doses than those prescribed for ED, and the two brand names are not interchangeable without medical guidance.