Viagra (Sildenafil)

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.

In men with erectile dysfunction, the enzyme PDE5 breaks down cGMP too rapidly, preventing the erection from developing or being sustained. 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)
• Are under 18 years of age

Dosage

Viagra is taken orally, approximately 30 to 60 minutes before anticipated sexual activity. It is available in three strengths:

Dose	Typical Use
25 mg	Starting dose for men aged 65 or over, or those with hepatic or renal impairment
50 mg	Standard starting dose for most adult men
100 mg	If 50 mg is well-tolerated but insufficiently effective

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.

Common side effects (may affect more than 1 in 10 people)

• Headache
• Flushing (warmth, redness, or tingling in the face and neck)
• Indigestion or dyspepsia
• Nasal congestion

Less common side effects (may affect up to 1 in 10 people)

• Visual disturbances (blurred vision, temporary blue-tinged vision, increased sensitivity to light)
• Dizziness
• Nausea
• Back pain

Serious side effects — seek immediate medical attention

• Sudden vision loss: Rare cases of non-arteritic anterior ischaemic optic neuropathy (NAION) have been reported. Stop taking sildenafil and seek urgent medical attention if sudden vision loss occurs.
• Sudden hearing loss: Stop treatment and contact a doctor immediately.
• Priapism: A prolonged erection lasting more than 4 hours (not related to sexual stimulation) is a medical emergency. Seek immediate medical attention to prevent permanent damage.
• Severe hypotension: Particularly if sildenafil is taken with nitrates or alcohol.
• Serious allergic reactions: Including skin rash, swelling of the face, lips, or throat, and difficulty breathing.

This is not a complete list. Refer to the EMA-approved product information for full prescribing details.

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.

Medicine	Active Ingredient	Onset	Duration	Dosing
Viagra	Sildenafil Citrate	30–60 min	4–6 hours	On demand
Cialis	Tadalafil	30–60 min	Up to 36 hours	On demand or daily
Levitra	Vardenafil	25–60 min	4–5 hours	On demand
Generic Viagra	Sildenafil	30–60 min	4–6 hours	On demand

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) has a slightly faster onset in some patients and may be suitable for men for whom sildenafil has been less effective. 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. The difference is in brand and price.

How to access Viagra online in Europe

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 EU-registered 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 EU-registered 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 licensed EU pharmacy partner. The pharmacy dispenses and ships the medicine directly to you.

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 use Viagra if you:

• Take any nitrate medicines (for example, glyceryl trinitrate, isosorbide mononitrate, or isosorbide dinitrate)
• Use recreational drugs containing nitrates (such as amyl nitrite or “poppers”)
• Have been told by a doctor to avoid sexual activity because of heart problems
• Are allergic to sildenafil or any other ingredient in Viagra
• Have severe liver disease

Tell your doctor before starting Viagra if you have:

• Heart disease or have recently had a heart attack or stroke
• Low blood pressure or uncontrolled high blood pressure
• A hereditary degenerative retinal disorder (such as retinitis pigmentosa)
• A history of priapism
• Sickle cell anaemia, multiple myeloma, or leukaemia
• Anatomical deformation of the penis (such as Peyronie’s disease)

Drug interactions: Viagra interacts with nitrates, alpha-blockers, antihypertensive medicines, CYP3A4 inhibitors (including ketoconazole, itraconazole, ritonavir, and saquinavir), and other PDE5 inhibitors. Always disclose all current medications and supplements to your doctor.

Avoid excessive alcohol consumption when taking Viagra, as alcohol can increase the risk of low blood pressure and reduce the medicine’s effectiveness.

Sources

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

• European Medicines Agency (EMA). Viagra (sildenafil) — Summary of Product Characteristics. Available at: ema.europa.eu
• European Medicines Agency (EMA). Assessment report: Viagra. EMEA/H/C/000202.
• World Health Organization (WHO). Sexual health — Fact sheet. who.int
• Goldstein I, et al. Oral sildenafil in the treatment of erectile dysfunction. N Engl J Med. 1998;338:1397-1404.

This content is reviewed periodically to reflect updated clinical guidance. 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.