Sildenafil Oral Tablets — Formulation, Dosing, and Practical Guidance

Tablet Information

How Viagra Pills Work — Forms, Strengths, and Practical Use

A Viagra pill is a film-coated oral tablet containing sildenafil citrate as its active ingredient, along with a number of inactive excipients — microcrystalline cellulose, calcium hydrogen phosphate, croscarmellose sodium, magnesium stearate, and the characteristic blue film coating. The tablet is designed for oral administration and is absorbed through the gastrointestinal tract, reaching the bloodstream within 30 to 60 minutes under typical conditions. It is taken on demand, meaning only before anticipated sexual activity rather than daily.

Three Strengths and When Each Is Used

Prescribers choose among three tablet strengths depending on the patient's age, health profile, current medications, and reported response to prior treatment:

  • 25 mg — prescribed for men who are older (generally over 65), have mild organ impairment, or take drugs that slow the liver's metabolism of sildenafil. Starting low minimizes side effects while the patient's response is assessed.
  • 50 mg — the standard starting dose for healthy adult men without significant comorbidities. It is the most commonly prescribed strength at initiation. Approximately 74% of men achieve satisfactory erections at this dose in controlled clinical trials.
  • 100 mg — the maximum approved single dose, used when 50 mg does not produce a sufficient response. Survey data from large registration trials show an improvement rate of approximately 82% at 100 mg. The trade-off is a meaningfully higher rate of side effects, particularly headache and flushing.

Dose adjustments should always be discussed with a prescribing physician. Taking two 50 mg tablets to approximate a 100 mg dose without medical guidance is neither safe nor advisable.

Brand-Name Tablets vs. Generic Sildenafil

The original Pfizer Viagra tablet — diamond-shaped and film-coated blue — is the branded product that most people recognize. Generic sildenafil tablets, which entered the US market after Pfizer's patent expired in December 2017, contain the same active molecule at the same dose. The FDA requires any generic to demonstrate bioequivalence with the brand-name reference before approval, meaning the peak plasma levels and absorption profiles must fall within an 80–125% range of the original (and in practice, most generics fall within 5% of equivalence).

The differences between brand and generic are limited to inactive ingredients — fillers, binders, and coatings — which vary between manufacturers. In a very small number of patients, a sensitivity to a specific excipient in one formulation may produce a different experience than another. This is uncommon. From a pharmacological standpoint, the two are clinically interchangeable for the treatment of erectile dysfunction.

How and When to Take the Tablet

Sildenafil should be swallowed whole with a full glass of water, approximately 30 to 60 minutes before sexual activity. Two practical points significantly affect how well it works in real-world use:

  • Food: a high-fat meal — a large dinner, for example, with red meat or fried food — can delay the time to peak absorption by up to one hour and reduce peak plasma levels by as much as 29%. Men who find the medication "doesn't work after dinner" are often experiencing this pharmacokinetic interaction rather than a resistance to the drug.
  • Alcohol: moderate consumption is generally tolerated, but heavy alcohol use can reduce erectile ability independently of the medication by suppressing the central nervous system, and it amplifies the blood-pressure-lowering effect of sildenafil, raising the risk of dizziness or fainting.

How Long Does One Tablet Last?

Sildenafil's half-life is approximately 3 to 5 hours. Most men find the therapeutic window falls within a 4 to 6 hour period after taking the tablet. The effect does not last all day; once the drug clears the system, the usual state of erectile function returns. Generally, one tablet per day is the maximum recommended frequency.

What to Know Before You Take It

Side Effects After Taking a Tablet

Most side effects from a sildenafil tablet appear within an hour of ingestion and resolve within four to six hours. The most commonly reported include:

  • Headache — reported by 15–16% of users taking 100 mg; caused by vasodilation in cerebral blood vessels. Over-the-counter pain relief (acetaminophen or ibuprofen) is generally effective.
  • Flushing — a feeling of warmth and redness in the face, neck, or chest; also vasodilation-related.
  • Nasal congestion — the nasal mucosa contains PDE5, so the drug's effect is not entirely tissue-specific.
  • Visual changes — a temporary blue or greenish tint to vision, light sensitivity, or blurred vision in a small percentage of users. This results from mild inhibition of PDE6 in the retina and is reversible as the drug clears.
  • Indigestion — reduced by taking the tablet with a small amount of food.

Serious adverse events are rare but include priapism (erection lasting over four hours — a medical emergency), sudden hearing loss, and sudden vision loss. Any of these require immediate medical attention.

Counterfeit Tablets: A Real Risk

Because the 100 mg strength is widely sought, it is also the most frequently counterfeited formulation in the global pharmaceutical supply chain. Laboratory analyses of counterfeit pills seized by regulators have found that they may contain no active ingredient at all, grossly incorrect doses of sildenafil, undeclared substances such as methamphetamine, or industrial compounds unsuitable for human consumption. The external appearance of a counterfeit tablet can be nearly indistinguishable from an authentic product.

This underscores the importance of obtaining sildenafil only from a licensed pharmacy operating under US regulatory oversight, where the drug originates from an FDA-approved manufacturing facility. Price alone is not a reliable indicator of authenticity — counterfeit pills sold at deeply discounted prices online are a well-documented problem.

Talking to a Pharmacist

When dispensing sildenafil for the first time, a pharmacist can provide practical guidance on timing, what to expect, and how specific medications you already take may interact with it. Disclosing your full medication list — including herbal supplements and over-the-counter drugs — is important because several commonly used medications affect sildenafil blood levels. CYP3A4 inhibitors (including certain antifungals, some antibiotics, and HIV protease inhibitors) can raise sildenafil levels significantly and may necessitate a dose reduction.

About This Page

This article is intended for informational purposes and does not constitute medical advice or a treatment recommendation. Clinical data and dosing details are drawn from FDA prescribing information for sildenafil citrate and peer-reviewed pharmacology sources. Reviewed by a medical writing team, April 2026.