Active ingredient: Sildenafil citrate

Primary use: management of erectile dysfunction (ED); also used in certain cases for pulmonary arterial hypertension under different dosing and brand names.

Available strengths commonly marketed: 100 mg and 50 mg tablets (some patients may be prescribed 25 mg based on tolerance and clinical need).

At a glance

  • Condition relevance: Erectile dysfunction; occasionally discussed in sport settings for altitude tolerance, though it is not a typical performance enhancer.
  • Onset and duration: Often begins working in about 30 minutes (some report benefit as early as 15–20 minutes); effects may last 4–6 hours.
  • Sexual stimulation is required: Sildenafil facilitates the physiological response but does not cause an erection without arousal.
  • Formulation note: "Viagra Professional" is a marketing term used by some sellers for sildenafil tablets; the FDA recognizes sildenafil citrate as the active drug, including brand Viagra and generics.

For details on how the medicine works, jump to How it works. If you want to understand the US legal requirements, see Legal status in the USA.

How it works

Sildenafil citrate inhibits phosphodiesterase type 5 (PDE5) in the corpus cavernosum. During sexual stimulation, nitric oxide (NO) triggers cyclic guanosine monophosphate (cGMP) production, causing relaxation of smooth muscle and increased penile blood flow. By slowing cGMP breakdown, sildenafil enhances this natural process, supporting erectile function in response to arousal.

In pulmonary arterial hypertension (a separate indication typically branded as Revatio), sildenafil reduces pulmonary vascular resistance through similar NO-cGMP mechanisms, but dosing and medical supervision differ from ED use.

How to use and dosing

General adult dosing for ED:

  • Start: 50 mg taken about 30 minutes before anticipated sexual activity (some providers start at 25 mg in older adults or in those with hepatic/renal impairment).
  • Adjust: 25 mg to 100 mg based on effectiveness and tolerability.
  • Frequency: Do not use more than once daily.
  • Food effects: A high-fat, heavy meal may delay onset. Consider taking on an empty stomach if you need a faster effect.
  • Grapefruit warning: Avoid grapefruit and grapefruit juice because they can raise sildenafil levels and side effects.

If you are taking alpha-blockers for prostate or blood pressure issues, your clinician may recommend a lower starting dose and careful timing due to blood pressure effects. For patients with pulmonary arterial hypertension, dosing is not interchangeable with ED dosing; follow your specialist's instructions.

More on risks and who should not take sildenafil is listed under Contraindications and Precautions.

Precautions

  • Cardiovascular assessment: If you have heart disease, recent stroke or heart attack, uncontrolled hypertension, or chest pain, seek medical evaluation before using ED medication.
  • Elderly sensitivity: Older adults may be more sensitive to blood pressure changes and adverse effects.
  • Vision or hearing changes: Stop the drug and seek urgent care if you experience sudden vision loss, a blue-tinted vision disturbance that is severe/persistent, or sudden hearing loss with or without tinnitus.
  • Priapism risk: Painful or prolonged erection over 4 hours is a medical emergency.
  • Alcohol: Moderate or avoid; alcohol can worsen dizziness and decrease erectile performance.
  • Allergies: Tell your clinician about any allergy to sildenafil or excipients.

Contraindications

  • Concurrent nitrate therapy (any form, such as nitroglycerin, isosorbide dinitrate/mononitrate) because of dangerous hypotension risk.
  • Use with soluble guanylate cyclase stimulators (for example riociguat).
  • Use with other PDE5 inhibitors or combining multiple ED medicines on the same day.
  • Known hypersensitivity to sildenafil or tablet components.
  • Not intended for women or for children for ED indications.

If any of the above apply to you, do not take sildenafil. Discuss safer alternatives listed under Alternatives and similar medicines.

Possible side effects

Many people experience mild or no adverse effects. Common and generally short-lived reactions may include:

  • Headache, facial flushing, nasal congestion
  • Indigestion or stomach upset
  • Dizziness or lightheadedness
  • Back or muscle aches (less common than with tadalafil)
  • Mild visual effects such as blue hue or increased light sensitivity
  • Diarrhea or nausea

Seek urgent medical care if you develop: chest pain, fainting, an erection lasting more than 4 hours, sudden vision or hearing loss, severe allergic reaction (rash, swelling of face/tongue/throat, severe dizziness, trouble breathing).

Drug and food interactions

  • Absolute avoidance: Nitrates and recreational "poppers" (amyl or butyl nitrite).
  • Soluble guanylate cyclase stimulators: riociguat and similar agents.
  • Alpha-blockers: may cause symptomatic hypotension; spacing and dose adjustments are needed.
  • Strong CYP3A4 inhibitors: ketoconazole, itraconazole, ritonavir, cobicistat, clarithromycin, grapefruit products; these can increase sildenafil levels.
  • Antihypertensives and alcohol: can enhance blood pressure lowering effects.
  • Other ED medications: do not combine sildenafil with tadalafil, vardenafil, or avanafil on the same day.

When in doubt, ask a pharmacist or clinician to review your full medication and supplement list.

Missed dose

Sildenafil for ED is taken only as needed. There is no routine schedule. Do not take extra tablets to compensate for a missed opportunity.

Overdose

Call emergency services immediately if you suspect an overdose. Symptoms may include severe dizziness or fainting, chest pain, rapid or irregular heartbeat, or persistent painful erection.

Storage

  • Temperature: store at 68–77 F (20–25 C).
  • Keep dry: protect from moisture and light.
  • Secure location: keep away from children and pets; do not store in bathrooms.

Alternatives and similar medicines

Several therapies are used for ED. Selection depends on onset preference, duration, side effect profile, medical history, and cost. Discuss with a clinician to choose the best option.

  • Tadalafil (brand Cialis; generic tadalafil) - Longer duration up to 36 hours; can be taken as needed (10 or 20 mg) or daily (2.5 or 5 mg).
  • Avanafil (brand Stendra) - Faster onset for some users (about 15 minutes); shorter duration than tadalafil.
  • Vardenafil (brand Levitra; orally disintegrating Staxyn) - Similar onset to sildenafil; ODT form is an option.
  • Sildenafil (brand Viagra; generic sildenafil) - Same active ingredient; multiple strengths. "Viagra Professional" in online markets typically refers to sildenafil with rapid-onset marketing claims, but the active substance is sildenafil citrate.
  • Non-oral options: Alprostadil injections (Caverject/Edex) or intraurethral suppository (Muse); vacuum erection devices; penile constriction rings; surgical implants for refractory cases.

For help comparing costs among these options, see Typical prices in USD.

Typical prices in USD (rough, subject to change)

Prices vary widely by pharmacy, insurance, dose, and coupon use. The estimates below reflect out-of-pocket retail or common coupon pricing in the USA:

  • Generic sildenafil 25/50/100 mg: about $0.50 to $4.00 per tablet; multi-tablet fills are usually cheaper per pill.
  • Brand Viagra 25/50/100 mg: about $60 to $80 per tablet.
  • Generic tadalafil 5/10/20 mg: roughly $0.20 to $3.00 per tablet; daily 5 mg can cost $6 to $60 per month depending on pharmacy and coupons.
  • Vardenafil generic 10/20 mg: typically $1 to $4 per tablet; brand Levitra often higher if available.
  • Avanafil (Stendra) 50/100/200 mg: often $20 to $60 per tablet.
  • Alprostadil (Caverject/Edex) injections: can range $70 to $100+ per dose; intraurethral Muse similar or higher depending on dose.

Tip: Check reputable pharmacies and price comparison tools. Telehealth services may bundle prescriptions with lower generic costs. Always verify legitimacy as described in Legal status in the USA.

Notes for athletes and sport settings

  • WADA status: As of the latest guidance, sildenafil is not prohibited by the World Anti-Doping Agency.
  • Altitude: Some athletes discuss sildenafil for high-altitude training; effects are variable and not guaranteed. Use only under medical advice.
  • Safety first: Combining with intense exercise when using alpha-blockers, nitrates, or in those with cardiovascular disease can be risky. Get a cardiovascular evaluation if unsure.

Helpful cross-links

New to this medication? Start with At a glance. Ready to take your dose? Recheck How to use and dosing. Worried about food and other drugs? Review Drug and food interactions. Looking for cost-saving options? Compare in Typical prices in USD. Concerned about safety? Read Contraindications and Precautions.

Important disclaimer

The information on this page is general and does not contain all possible directions, interactions, or precautions. It is not a substitute for professional medical advice, diagnosis, or treatment. Always follow the instructions from your own clinician and pharmacist, which may differ based on your health history. We are not responsible for any harm resulting from reliance on the information provided here or from self-treatment. If you suspect a medical emergency, call emergency services immediately.

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