Viagra (Sildenafil Citrate)

What is Viagra?

Viagra (sildenafil citrate) is a prescription-only oral medicine approved by the European Medicines Agency (EMA) for the treatment of erectile dysfunction (ED) in adult men. It was the first oral PDE5 inhibitor approved for this indication and has been prescribed globally for over two decades, accumulating a well-established clinical safety and efficacy profile.

Sildenafil citrate is the active ingredient in Viagra and is also available as a generic medicine under the name sildenafil.

How does Viagra work?

Viagra belongs to a class of medicines called phosphodiesterase type 5 (PDE5) inhibitors. Erections are achieved through a sequence of physiological events: sexual stimulation triggers the release of nitric oxide in penile tissue, which activates an enzyme that produces cyclic guanosine monophosphate (cGMP). cGMP relaxes smooth muscle cells in the blood vessels of the penis, allowing increased blood flow and producing an erection.

PDE5 normally breaks down cGMP. Erectile dysfunction has multiple possible causes; excessive PDE5 activity is not a universal explanation. Sildenafil inhibits PDE5, allowing cGMP to accumulate and supporting normal erectile function in response to sexual stimulation.

Key point: Viagra does not produce an erection on its own. Sexual stimulation is required for the medicine to be effective.

Who is Viagra for?

Viagra is indicated for adult men experiencing erectile dysfunction — defined by the EMA as the persistent or recurrent inability to attain or maintain a penile erection sufficient for satisfactory sexual performance.

ED may have physical causes (cardiovascular disease, diabetes, hormonal imbalances, neurological conditions), psychological causes (anxiety, depression, relationship factors), or a combination of both. A medical assessment is required to determine whether sildenafil is an appropriate and safe treatment option for an individual patient.

Viagra is not appropriate for everyone. It is contraindicated in men who:

• Take nitrate medicines in any form (including short-acting nitroglycerin tablets)
• Have been advised to avoid sexual activity for cardiac reasons
• Have severe hepatic impairment
• Have a history of non-arteritic anterior ischaemic optic neuropathy (NAION)
• Take riociguat or have other contraindications listed in the safety section below

Viagra is not indicated for people under 18 years.

Dosage

Viagra is taken orally, approximately one hour before anticipated sexual activity. It is available in three strengths:

The maximum recommended dose is 100 mg per day. Viagra should not be taken more than once in a 24-hour period.

Taking Viagra on an empty stomach or with a light, low-fat meal generally produces a faster onset of action. A high-fat meal can delay absorption by up to 60 minutes and reduce peak plasma concentrations.

Patients should not adjust their dose without consulting their prescribing doctor.

Side effects

As with all medicines, Viagra may cause side effects. Not every patient experiences them.

Very common

• Headache

Common

• Flushing, indigestion, nasal congestion
• Dizziness, nausea, altered colour vision or blurred vision

Uncommon

• Light sensitivity and muscle pain

Serious effects — seek immediate medical attention

• An erection lasting more than 4 hours: seek emergency care regardless of sexual stimulation.
• Sudden visual impairment or hearing loss: stop sildenafil and seek immediate medical advice.
• Severe allergic reaction, chest pain or marked hypotension: seek urgent care. Do not self-treat chest pain with nitrates; tell emergency staff when sildenafil was taken.

This is not a complete list; use the selected product information.

Viagra vs alternatives

Several PDE5 inhibitors are approved in Europe for erectile dysfunction. The table below provides a factual comparison for informational purposes only. A doctor must assess which, if any, of these medicines is clinically appropriate for an individual patient.

Key differences:

• Viagra vs Cialis: Tadalafil (Cialis) has a significantly longer duration of action (up to 36 hours versus 4–6 hours for sildenafil), and is also available as a low-dose daily tablet for continuous effect. Sildenafil onset of action is broadly similar.
• Viagra vs Levitra: Vardenafil (Levitra) is a different active substance; a doctor must assess any change. Both have a comparable duration of action.
• Viagra vs Generic Sildenafil: Generic sildenafil contains the same active ingredient at the same doses and has the same clinical efficacy. Excipients and individual tolerability may differ; the actual product information must be checked.

Online assessment for Viagra (Sildenafil Citrate)

Viagra is a prescription-only medicine (POM) in all EU member states. It cannot be legally dispensed without a valid prescription from a licensed medical professional.

Prescrivia operates as a technology intermediary: we do not prescribe medicines, employ doctors, or sell medicines. Our platform connects patients with independent doctors who can conduct confidential online health assessments.

The process works as follows:

1. Complete a health assessment: Answer a structured set of health questions covering your medical history, current medications, and relevant lifestyle factors. This assessment is reviewed by an independent doctor.
2. Doctor review: An independent doctor reviews your assessment. If sildenafil citrate is clinically appropriate, they may issue a prescription. If it is not appropriate, the doctor will explain why.
3. Prescription and fulfilment: If a prescription is issued, it is sent to a pharmacy partner. The pharmacy is responsible for dispensing under national rules; this article does not establish delivery or stock.

Important: Prescrivia does not guarantee that a prescription will be issued. All prescribing decisions are made independently by qualified medical professionals based on individual clinical circumstances.

Important safety information

Do not take sildenafil if you:

• Use nitrates or nitric oxide donors, including recreational nitrites (poppers)
• Take riociguat
• Have been advised to avoid sexual activity for cardiac reasons
• Have severe liver impairment
• Have blood pressure below 90/50 mmHg, a recent stroke or heart attack, or a hereditary degenerative retinal disorder such as retinitis pigmentosa
• Have lost vision in one eye because of NAION, whether or not linked to a previous PDE5 inhibitor
• Are allergic to sildenafil or an excipient

Precautions to discuss: Other heart disease or blood-pressure problems, kidney or liver disease, bleeding disorders or active peptic ulcer, previous priapism, sickle cell anaemia, myeloma, leukaemia or penile deformity.

Interactions: Ritonavir co-administration is not recommended. With other CYP3A4 inhibitors, consider a 25 mg starting dose. Patients on alpha-blockers must be stable before sildenafil starts; consider 25 mg to reduce postural hypotension risk. Do not combine with other PDE5 inhibitors or ED treatments. Do not stop another medicine yourself. Disclose all medicines and supplements.

Avoid excess alcohol. Know how sildenafil affects vision or balance before driving. The selected product leaflet must be checked for excipients and all warnings.

In Spain, distance sale of prescription medicines is prohibited under Article 3.5 of Royal Legislative Decree 1/2015. An online assessment does not remove this restriction. Dispensing and access depend on the exact product and applicable national rules.

Sources

Medical information on this page is based on the following sources:

• AEMPS: Viagra film-coated tablets, sections 4.1–4.8.
• EMA: questions and answers on generic medicines.

This editorial summary does not replace the full product information. It is provided for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for advice relevant to your individual health circumstances.