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Molecule Description

Sold under the common name of Viagra, Sildenafil is a Phosphodiesterase inhibitor used for the treatment of erectile dysfunction.

Uses of Sildenafil

  • Erectile dysfunction, also known as impotence, erectile dysfunction is an inability to develop or maintain proper penile erection to perform sexual activity
  • Pulmonary arterial hypertension is a health complication marked by increased blood pressure in the arteries connected to the heart

Contraindications of Sildenafil

When should one not use Sildenafil

  • Regular smokers are not advised to take Sildenafil as it leads to severe side effect of eye called NAION meaning excessive blood loss in optic nerve
  • Patients who experience heart attacks, low blood pressure, myocardial infraction, stroke and cardiac failure are also advised to avoid the use of Sildenafil to prevent serious effects
  • Sildenafil is recommended for the individuals having penile deformities
  • If you have rare inherited eye diseases (retinitis pigmentosa)
  • Sildenafil is not recommended for the treatment of individuals reported with a hypersensitivity for the drug, for who have received treatment with medicine containing nitrates
  • Sildenafil is not recommended for the treatment of patients less than 18 year old
  • If you have a stomach ulcer or bleeding problem (haemophilia)

Side effects of Sildenafil

Common side effects of this drug are:

  • Headache
  • Nausea
  • Muscle aches
  • Flushing
  • Tenderness around eyes or cheekbones
  • Sneezing
  • Runny or bloody nose
  • Unusually warm skin
  • Troubled breathing
  • Reddening of skin
  • Stomach discomfort
  • Pounding heartbeat
  • Burning or itching sensation at various body parts
  • Bloody or cloudy urine
  • Cold sweats
  • Confusion
  • Convulsions
  • Difficulty in concentration
  • Drowsiness
  • Dry mouth, eyes, and skin
  • Dizziness
  • Chest pain
  • Increased hunger
  • Increased urination frequency
  • Indigestion
  • Tenderness at stomach
  • Anxiety
  • Nightmares
  • Migraine
  • Prolonged and painful erection
  • Behavioural changes
  • Bloodshot eyes/red eyes, pain in the eyes, seeing flashes of light, light sensitivity, watery eyes
  • Fainting
  • Low blood pressure

Precautions and Warnings of Sildenafil


Can I take Sildenafil during pregnancy?
Sildenafil is a medicine used to treat erectile dysfunction in male. Thus, it is not recommended to administer in pregnant women.

Breast Feeding

Can I take Sildenafil while breastfeeding?
Sildenafil is not recommended to administer in breastfeeding mothers.


Can I drive if I have consumed Sildenafil?
Sildenafil can cause dizziness and can affect your vision. You should be careful if you need to drive.


Can I consume alcohol with Sildenafil?
Drinking alcohol is known to cause erection impairment. You are advised not to drink alcohol in extreme amounts before taking Sildenafil.

Other General Warnings

Talk to your doctor if
  • You experience sudden loss of hearing or buzzing noise in ears while taking treatment with Sildenafil
  • Some patients may experience a sudden loss of vision while taking a treatment with Sildenafil. In such a situation, stop taking Sildenafil and consult a physician immediately
  • Sildenafil should be used with great caution for the treatment of heart patients
  • The risk of side effects caused by Sildenafil is great in case of regular smokers, patients older than 60 years and heart patients
  • Sildenafil may result into priapism, i.e. painful erection especially in patients suffering from sickle cell anaemia (an abnormality of red blood cells), leukaemia (cancer of blood cells), multiple myeloma (cancer of bone marrow) and penile deformities
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Mode of Action of Sildenafil

How Does It Work?

Human erection is an involuntary event governed by the autonomous nervous system. On stimulation, two essential parts of the human penis, corpus carvernosum and corpus spongium create the erection by maintaining blood flow. One more factor that plays a crucial role in regulating erection is cyclic Guanosine monophosphate (cGMP), which increases the blood flow in the penis, causing an erection. In people who have erectile dysfunction, cGMP-specific Phosphodiesterase type 5 (PDE5) binds cGMP and inhibits its action. Sildenafil protects this degradation of cGMP by PDE5 in corpus cavernosum. Sildenafil has the same structure as cGMP and it binds PDE5, which eventually results in free cGMP resulting in undisturbed erection.
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Interactions of Sildenafil

Interactions with other medicines

  • Concomitant administration of Sildenafil and medicines containing nitrates leads to dangerous hypotensive effects (low blood pressure)
  • Coadministration of Sildenafil and alpha-blockers lowers the blood pressure
  • Sildenafil interact with Amlodipine and cause an increase in blood pressure
  • Coadministration of Sildenafil and CYP3A4 inhibitors like Ritonavir (medicine for HIV treatment) increase the systemic exposure of Sildenafil
  • Coadministration of Sildenafil with Ritonavir is not advised

Interactions with food items

Sildenafil leads to dangerous effects when consumed with grapefruit or its juice and pomelo or its juice.

Dietary Restrictions of Sildenafil

Patients taking a treatment with Sildenafil are advised to avoid grapefruit or its products.

Dosage of Sildenafil


Symptoms of overdose can be headache, flushing, dizziness, dyspepsia, nasal congestion, altered vision. Call emergency medical services if you suspect overdose.

Missed a Dose

In case of a missed dose, patients are recommended to take the dose as soon as possible. However, if the time of the next dose has already come, the patient can skip the missed dose and continue with their scheduled dosages.
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Content Details


Dr. Arpit Verma

MBBS, MD (Pharmacology)


Dr. Ritu Budania

MBBS, MD (Pharmacology)

Frequently Asked Questions (FAQs)


Q: On administering this medicine, when does its effect start to show?

A: The effect of Sildenafil can be observed within 30 to 120 minutes of its administration.

Q: What is the duration of its effect?

  • The duration of the effect of Sildenafil is 4 hours.

Q: Is it safe with alcohol?

A: No, Sildenafil and alcohol interact with each other and lead to an increase in the risk as well as the intensity of side effects like dizziness, fainting, flushing, headache, etc.

Q: Does it have habit-forming tendencies?

A: No habit-forming tendencies are reported in case of Sildenafil.

Q: What should you tell your doctor before you start the medication of Sildenafil?

A: You must inform the doctor about heart diseases, asthma, blood pressure disorders, diabetes and congenital penile defects (if any) to your doctor before taking a treatment with Sildenafil.
Last Updated on: 05 Oct 2020 | 10:47 PM (IST)

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The information provided herein is accurate, updated and complete as per the best practices of the Company. Please note that this information should not be treated as a replacement for physical medical consultation or advice. We do not guarantee the accuracy and the completeness of the information so provided. The absence of any information and/or warning to any drug shall not be considered and assumed as an implied assurance of the Company. We do not take any responsibility for the consequences arising out of the aforementioned information and strongly recommend you for a physical consultation in case of any queries or doubts. Please click here for detailed T&C.
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