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Home/Drugs/Viagra

Viagra: Uses, dosage, side effects, warnings & patient reviews

Viagra

Viagra
Viagra 100 mg
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Viagra

Sildenafil citrate
Viagra is a prescription medication containing the active pharmaceutical ingredient sildenafil citrate. It is indicated for the treatment of erectile dysfunction (ED) in adult men.
  • ActiveIngredient: Sildenafil citrate
  • DosageForm: Film-coated tablets
  • Dosage: 25 mg, 50 mg, 100 mg.
  • Indications: Treatment of erectile dysfunction (ED).
  • Manufacturer: Pfizer Inc. (Brand); generic manufacturers include Teva Pharmaceuticals, Viatris (Mylan), Amneal Pharmaceuticals, and Aurobindo Pharma.
  • Storage: Store at room temperature 20°C–25°C (68°F–77°F); excursions permitted to 15°C–30°C (59°F–86°F).
  • Drug Status: Prescription Only
Description

What is Viagra (Sildenafil)?

Viagra is an oral tablet belonging to the class of medications known as phosphodiesterase type 5 (PDE5) inhibitors. Its active component, sildenafil citrate, was originally developed and continues to be used for pulmonary arterial hypertension under a different brand name.

For the management of erectile dysfunction (ED), Viagra works by inhibiting the PDE5 enzyme. This action enhances the natural erectile response to sexual stimulation by increasing blood flow to the corpus cavernosum of the penis.

Following the expiration of its patent, the active ingredient sildenafil became available in numerous generic formulations. These generic Viagra products, such as Cenforce, contain the same active ingredient in equivalent dosages and are subject to regulatory standards for bioequivalence.

General Instructions

How to Take Viagra

Administration of Viagra must follow the specific instructions provided by the prescribing healthcare professional. The following represents standard clinical guidance.

Dosage and Administration

The recommended starting dose for most patients is 50 mg, taken as needed, approximately one hour before sexual activity. Based on efficacy and tolerability, the dose may be increased to 100 mg or decreased to 25 mg. The maximum recommended dose is 100 mg, and dosing should not exceed once per 24-hour period.

Viagra can be taken with or without food. However, administration with a high-fat meal may delay the onset of action by reducing the rate of absorption.

Duration of Effect

The therapeutic window for Viagra is typically up to four hours following administration. It does not cause an automatic erection; sexual stimulation is required for the medication to be effective.

Side Effects

Side Effects of Viagra

Adverse reactions are categorized by frequency. For a clinical perspective on common side effects, see the overview of ED pill side effects.

Common and Serious Adverse Reactions for Viagra (Sildenafil)
FrequencyReported Side EffectsClinical Notes
Very Common (>1 in 10)Headache, flushing, dyspepsia.These effects are usually mild to moderate and transient.
Common (1 in 10 to 1 in 100)Nasal congestion, dizziness, visual disturbances (e.g., color tinge, blurred vision), back pain, myalgia, nausea.Visual disturbances are related to mild, transient inhibition of PDE6 in the retina.
Uncommon to Rare (Serious)
  • Priapism: Erection lasting >4 hours.
  • Sudden hearing loss or decrease.
  • Non-arteritic anterior ischemic optic neuropathy (NAION), presenting as sudden vision loss.
  • Serious cardiovascular events (e.g., myocardial infarction) in patients with pre-existing cardiac risk during sexual activity.
  • Severe hypersensitivity reactions.

Priapism, sudden vision loss, and sudden hearing loss are medical emergencies requiring immediate intervention. Discontinue Viagra and seek urgent medical care.

Uses

What is Viagra Used For?

FDA-Approved Indication

Viagra (sildenafil) is indicated for the treatment of erectile dysfunction (ED). It is prescribed for adult men who have been medically evaluated for this condition.

Mechanism in Erectile Dysfunction

During sexual stimulation, nitric oxide is released, leading to increased levels of cyclic guanosine monophosphate (cGMP) in the penile smooth muscle. cGMP causes relaxation and inflow of blood. Viagra inhibits the PDE5 enzyme, which degrades cGMP, thereby enhancing the natural erectile response. It is not an aphrodisiac and does not increase libido.

Comparison with Other Therapies

Treatment choice depends on individual patient factors, including desired duration of effect, frequency of intercourse, and co-morbidities. Cialis (tadalafil), another PDE5 inhibitor, has a longer half-life. For a clinical comparison, see the guide on Viagra vs. Cialis.

Interactions Alcohol:

Unsafe
Alcohol is a vasodilator and may potentiate the blood pressure-lowering effects of Viagra, increasing the risk of dizziness, headache, and tachycardia. Consumption may also impair the ability to achieve an erection. For detailed clinical advice, see the analysis on alcohol interaction with Viagra.

Interactions Other Medications:

Consult your doctor
Concomitant use is contraindicated with any form of organic nitrate or nitric oxide donor due to the risk of severe hypotension. Concurrent use with alpha-blockers requires caution and appropriate dosing separation due to additive blood pressure effects. Comprehensive guidance is available in the safety guide to ED pill interactions.

Special Groups Pregnancy:

Unsafe
Viagra is not indicated for use by women. It is contraindicated during pregnancy.

Special Groups Breastfeeding:

Unsafe
Viagra is not indicated for use by women and should not be used while breastfeeding.

Special Groups Elderly:

Use with caution
No dose adjustment is solely based on age. However, elderly patients may have increased sensitivity to sildenafil, a higher incidence of cardiovascular conditions, and potential for altered clearance. A lower starting dose (25 mg) may be considered.

Special Groups Children:

Unsafe
Viagra is not indicated for use in pediatric populations for the treatment of ED.

Effects on Activities Driving:

Use with caution
Patients should be aware of possible dizziness, syncope, or visual disturbances and should assess their individual response before driving or operating machinery.

Effects on Activities Operating Machinery:

Use with caution
The same precautions as for driving apply. Impairment from vasodilatory symptoms can pose a risk when operating machinery.
Concerns

Important Safety Concerns

Cardiovascular Risk Assessment

Sexual activity carries a potential cardiac risk. Physicians should consider the cardiovascular status of patients prior to initiating any treatment for ED. Viagra has systemic vasodilatory properties and causes a mild, transient decrease in blood pressure. It is contraindicated in men for whom sexual activity is inadvisable due to significant underlying cardiovascular pathology.

Ocular and Otic Adverse Events

Rare cases of NAION, a cause of permanent vision loss, have been reported post-marketing in temporal association with PDE5 inhibitor use. Patients with a history of NAION have an increased risk. Sudden decrease or loss of hearing has also been reported, which may be accompanied by tinnitus and dizziness.

Priapism and Prolonged Erection

Erections lasting longer than 4 hours require immediate medical attention to avoid long-term sequelae such as penile tissue damage and permanent erectile dysfunction. Patients with conditions predisposing to priapism (e.g., sickle cell anemia, multiple myeloma, leukemia) should use Viagra with caution.

Non-Arteritic Anterior Ischemic Optic Neuropathy (NAION)

Physicians should advise patients to stop use of all PDE5 inhibitors and seek immediate medical attention in the event of sudden vision loss in one or both eyes.

Warnings

Critical Warnings and Contraindications

Contraindication with Nitrates

Viagra is strictly contraindicated in patients using any form of organic nitrate or nitric oxide donor, either regularly or intermittently. This includes nitroglycerin, isosorbide mononitrate/dinitrate, and recreational amyl nitrite (“poppers”). Concomitant use can result in a profound and life-threatening drop in blood pressure.

Cardiovascular Status

Due to the mild hypotensive effects of Viagra and the cardiac workload associated with sexual activity, it is not recommended for men with:

  • Unstable angina or angina during sexual intercourse.
  • Heart failure (NYHA Class II or greater).
  • Recent myocardial infarction or stroke.
  • Uncontrolled arrhythmias, hypotension (<90/50 mm Hg), or uncontrolled hypertension.

Use Without Erectile Dysfunction

Viagra is a prescription medication for a diagnosed medical condition. Its use by individuals without erectile dysfunction, particularly for recreational purposes, is not medically indicated and carries risks including dependence, adverse effects from unregulated sources, and psychological effects. See the warning against recreational use of Viagra.

Concomitant Use with Alpha-Blockers

Both alpha-blockers and Viagra lower blood pressure. To minimize the risk of symptomatic hypotension, Viagra should be initiated at the lowest dose (25 mg) only after the patient is hemodynamically stable on their alpha-blocker therapy.

Effects on the Eye

Patients should be informed about the potential for mild, transient visual disturbances (changes in color perception, blurred vision). Those with inherited retinal disorders such as retinitis pigmentosa should use Viagra with caution due to a theoretical risk.

Dosage

Viagra Dosage Information

Dosage must be individualized under medical supervision based on efficacy and tolerability.

Viagra (Sildenafil) Dosage Guidelines for Erectile Dysfunction
Dosage StrengthIndication and UseAdministration Notes
Viagra 25 mgRecommended starting dose for patients with hepatic impairment, severe renal impairment (CrCl <30 mL/min), the elderly, and those taking potent CYP3A4 inhibitors (e.g., ketoconazole, ritonavir).Assess tolerability before considering a dose increase.
Viagra 50 mgThe standard recommended starting dose for most patients.Take approximately 1 hour before sexual activity, but may be taken 30 minutes to 4 hours prior.
Viagra 100 mgMaximum recommended dose. Used if the 50 mg dose is well-tolerated but insufficiently effective.Do not exceed once daily. Not recommended as a starting dose.

Important Administration Notes

  • Maximum Frequency: One dose per 24-hour period.
  • Food Interaction: A high-fat meal delays the rate of absorption (Tmax) and reduces peak concentration (Cmax) by approximately 30%.
  • Sexual Stimulation: Required for efficacy.
Interactions

Drug Interactions with Viagra

Sildenafil is primarily metabolized by the hepatic cytochrome P450 enzyme CYP3A4. Concomitant use with inducers or inhibitors of this pathway can alter plasma concentrations.

Significant Drug Interactions with Viagra (Sildenafil)
Interacting Substance ClassExamplesEffect and Management
Nitrates (Contraindicated)Nitroglycerin, isosorbide mononitrate, amyl nitrite.Absolute contraindication. Risk of severe, potentially fatal hypotension.
Potent CYP3A4 InhibitorsKetoconazole, itraconazole, ritonavir, clarithromycin.Increase sildenafil plasma levels. Maximum Viagra dose should be limited to 25 mg in a 48-hour period.
Alpha-Adrenergic Blocking AgentsTamsulosin, doxazosin, terazosin.Additive blood pressure-lowering effects. Initiate Viagra at 25 mg only when hemodynamic stability on alpha-blocker is achieved.
Other AntihypertensivesACE inhibitors, beta-blockers, calcium channel blockers, diuretics.Potential additive hypotensive effect. Monitor blood pressure.
Guanylate Cyclase (GC) StimulatorsRiociguat.Contraindicated. Concomitant use may cause symptomatic hypotension.

FAQs

Ineffectiveness can be due to incorrect dosing, high-fat food consumption, lack of adequate sexual stimulation, or psychological factors. Do not increase the dose independently. Consult your healthcare provider. They may adjust the dose, provide administration guidance, or discuss alternative treatments. For a comprehensive overview of next steps, see the guide on managing lack of efficacy.
Following patent expiration, other manufacturers can produce bioequivalent versions without the initial research, development, and marketing costs associated with the brand-name drug. These generic medicines must demonstrate the same active ingredient, strength, dosage form, and pharmacokinetic profile as the reference product.
Yes. In addition to standard film-coated tablets, other formulations exist, such as Viagra Soft (chewable) and Viagra Professional, which are marketed as having different absorption characteristics.
Sildenafil is not approved for treating sexual dysfunction in women. The medication often referred to as "female Viagra" is flibanserin (Addyi), which has a different mechanism and indication. Information is available on treatments for female sexual dysfunction.
Viagra is a prescription medication. It should only be obtained through a licensed pharmacy with a valid prescription from a healthcare provider who has conducted an appropriate medical evaluation. Purchasing from unverified online sources poses significant risks, including counterfeit products with incorrect ingredients or dosages.
Other Details

Additional Information

Pharmacology Overview

Sildenafil is a selective inhibitor of phosphodiesterase type 5 (PDE5). By inhibiting PDE5 in the corpus cavernosum, it increases intracellular levels of cGMP, enhancing smooth muscle relaxation and blood inflow in response to sexual stimulation.

Pharmacokinetics

Sildenafil is rapidly absorbed after oral administration, with a median time to maximum plasma concentration (Tmax) of 60 minutes when taken in a fasted state. The terminal half-life is approximately 3-5 hours. It is metabolized predominantly by CYP3A4 and excreted mainly in the feces.

References

References and Medical Sources

  1. U.S. Food and Drug Administration (FDA). VIAGRA® (sildenafil citrate) Prescribing Information. [Revised 2014]. https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/20895s039s042lbl.pdf
  2. European Medicines Agency (EMA). Viagra: EPAR – Product Information. [Updated 2023]. https://www.ema.europa.eu/en/documents/product-information/viagra-epar-product-information_en.pdf
  3. American Urological Association (AUA). Management of Erectile Dysfunction (2018). https://www.auanet.org/guidelines/guidelines/erectile-dysfunction-(ed)-guideline
  4. DailyMed. Sildenafil Citrate – Drug Label. U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b48630b1-5208-4d00-b56f-21701f223758
Disclaimer

Disclaimer: The information on this site is provided for informational purposes only and is not medical advice. It does not replace professional medical consultation, diagnosis, or treatment. Do not self-medicate based on the information presented on this site. Always consult with a doctor or other qualified healthcare professional before making any decisions about your health.

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