Important Safety Information for Sildenafil

What Sildenafil Is Used For

Sildenafil is a prescription medication used to treat erectile dysfunction (ED). It belongs to a group of medicines called phosphodiesterase type-5 (PDE5) inhibitors, which work by improving blood flow to the penis and helping men achieve and maintain an erection suitable for sexual activity.

Who Should Not Take Sildenafil

Sildenafil may not be appropriate for everyone. Do not take sildenafil if you:

  • Use medications that release nitric oxide such as nitrates or nitrites, as combining them may cause a dangerous drop in blood pressure. Nitrates must not be taken within 48 hours after the last dose of tadalafil.
  • Take guanylate cyclase (GC) stimulators such as riociguat.
  • Have a known allergy or hypersensitivity to sildenafil or any of its ingredients.

How to Take Sildenafil

Sildenafil is typically taken 30 minutes to 1 hour before sexual activity. It may be taken with or without food, although heavy meals may delay its effects.

Do not take more than one dose within a 24-hour period and avoid combining it with other erectile dysfunction medications or PDE5 inhibitors during that time.

What to Tell Your Healthcare Provider

Before using sildenafil, inform your healthcare provider about all medications you are currently taking, including prescription drugs, over-the-counter medicines, supplements, and herbal products. Sildenafil can interact with certain medications and may lead to serious side effects.

Extra caution is needed if you are taking:

  • Nitrates
  • Alpha-blockers
  • Blood pressure medications
  • Certain CYP3A4 inhibitors such as ritonavir or ketoconazole
  • Consume large amounts of alcohol, as this may increase the risk of dizziness, low blood pressure, or fainting.

You should also share your full medical history, particularly if you have or have had:

  • Cardiovascular conditions such as heart attack, stroke, chest pain, or abnormal blood pressure.
  • Eye disorders including sudden vision loss or retinitis pigmentosa.
  • Bleeding disorders or stomach ulcers.
  • Liver or kidney disease.
  • A history or risk of priapism (a prolonged and painful erection lasting more than 4 hours).

Dose Adjustments 

If you are taking ritonavir, sildenafil levels can increase significantly.

  • Do not exceed 25 mg within 48 hours

For other strong CYP3A4 inhibitors, a lower starting dose (25 mg) may be recommended.

Serious Side Effects to Watch For

If you experience a medical emergency, seek immediate medical attention.

  • Cardiovascular risk: Sexual activity places stress on the heart. Sildenafil should not be used by individuals for whom sexual activity is not recommended due to underlying heart conditions.
  • Prolonged erection (priapism): Seek emergency medical care if an erection lasts longer than 4 hours.
  • Vision problems: Stop the medication and seek medical attention if you experience sudden vision loss in one or both eyes. This may be a sign of non-arteritic anterior ischemic optic neuropathy (NAION).
  • Sudden hearing loss: Discontinue the medication and seek prompt medical care if you notice sudden hearing loss or ringing in the ears.
  • Low blood pressure: Taking sildenafil with alpha-blockers or other blood-pressure-lowering medicines may lead to dizziness, fainting, or lightheadedness due to a drop in blood pressure.
  • Interaction with ritonavir: Ritonavir may increase sildenafil levels in the body, which could increase the risk of low blood pressure, fainting, or prolonged erection.
  • Use with other ED medications: Do not take sildenafil more than once within 24 hours or together with other PDE-5 inhibitors.
  • Bleeding risk: Sildenafil alone does not typically affect bleeding time, but rare bleeding events have been reported.
  • Sexually transmitted infections: Sildenafil does not protect against sexually transmitted infections (STIs). Safe sex practices are recommended.

Common Side Effects

Some users may experience mild side effects while taking sildenafil, including:

  • Headache
  • Facial flushing
  • Indigestion
  • Nasal congestion
  • Changes in vision
  • Back pain
  • Muscle pain
  • Nausea
  • Dizziness
  • Skin rash

Related information

This page is provided for informational purposes only. Always consult a licensed healthcare provider before starting any treatment.