How does sildenafil work in erectile dysfunction?

It is a phosphodiesterase-5 (PDE5) inhibitor. It relaxes smooth muscle in the penile vessels, facilitating an erection in response to sexual stimulation. It does not cause spontaneous erections.

What precautions apply to sildenafil?

It must not be combined with nitrates (e.g. for angina) or with alpha-blockers without supervision. The doctor reviews your cardiovascular health, current medication and contraindications before prescribing.

How does it differ from tadalafil?

Sildenafil acts fast but lasts 4–6 h; tadalafil is slower and lasts up to 36 h. The choice depends on frequency and desired spontaneity. The doctor discusses this with you.

Can I get a consultation for Sildenafil from Madrid?

Yes. Hi-Doctor runs 100 % online across the EU, so if you live in Madrid you can fill in the questionnaire and receive the medical review without travelling. The electronic prescription issued by the licensed doctor is valid in any EU pharmacy under Directive 2011/24/EU; in Spain it is dispensed directly from the prescription QR.

Is my sexual health consultation fully confidential?

Yes. All communication happens in the private chat of your account, GDPR-compliant. The doctor treats discretion as a core of the service and there is no history visible outside your consultation.

What is the private electronic prescription and why is it valid across the EU?

The private electronic prescription (Receta Médica Privada Electrónica) is issued by a licensed doctor in Spain. It is a PDF carrying every field required by EU Directive 2011/24/EU (patient, prescriber with country of registration, active ingredient, dose), which makes it legally recognised across all 27 EU member states. In Spanish pharmacies it is dispensed from the QR; outside Spain, the pharmacist dispenses the locally marketed equivalent of the same active ingredient.

How does Hi-Doctor work step by step?

1) Fill in an online medical questionnaire in about 4 minutes. 2) An EU-licensed doctor reviews your case and replies in under 24 h through the private chat in your account. 3) If eligible, the doctor issues an electronic prescription. 4) You collect it at any EU pharmacy. The consultation costs €25 and, if the doctor decides it is not safe to prescribe, the full amount is refunded.

How much does it cost and what does the price include?

The medical consultation costs €25 and includes a licensed doctor's review of your case and, if approved, the electronic prescription. If the doctor decides the treatment is not appropriate, the €25 is refunded. The medication price is separate and paid at the pharmacy; it varies by country, pharmacy and product across the EU. Because your electronic prescription is valid at any EU pharmacy, you can compare and choose where to fill it.

SildenafilPrescription only

Online medical consultation for Sildenafil.

An EU-licensed doctor reviews your case and, if eligible, issues an electronic prescription valid at any EU pharmacy under Directive 2011/24/EU.

Onset in 30–60 minutes
Effect window of ~4–6 hours
The best-known, most-studied PDE5

€25Refund if treatment not approved

Start consultation · €25 See how it works

Medication, if prescribed, is dispensed and paid for separately at a pharmacy.

FormOral tablet

FrequencyOn demand

ResultsActs in 30–60 minutes

StatusPrescription only

About

What is Sildenafil?

Active ingredient: Sildenafil · Dosages: 25 / 50 / 100 mg on demand

Sildenafil is a phosphodiesterase-5 (PDE5) inhibitor. It relaxes smooth muscle in the penile blood vessels, facilitating an erection in response to sexual stimulation — it does not cause spontaneous erections or change desire.

It's taken on demand, 30 to 60 minutes before sexual activity; high-fat meals can delay onset. The doctor prescribes the appropriate dose after reviewing your cardiovascular health, current medication and contraindications.

How it works in the body

By inhibiting the PDE5 enzyme, sildenafil improves blood flow to the penis when there is sexual stimulation. Its effect starts within 30–60 minutes and lasts around 4–6 hours.

How it helps

How it helps.

Works on demand

Taken 30–60 minutes before sex — no daily routine required.

Adjustable dose

25, 50 or 100 mg — the doctor prescribes what fits your case and tolerance.

Doctor-screened

Cardiovascular health and interactions are reviewed before any prescription.

What to expect

How to take it.

On demand, before sexual activity. The doctor sets your dose and reviews it with you if the response or tolerance isn't right.

Take it 30–60 minutes before sexual activity
Avoid heavy, high-fat meals right before — they delay onset
Never combine with nitrates
Message your doctor to adjust the dose if needed

Doses your doctor can prescribe

Available doses25 / 50 / 100 mg
When30–60 min before activity
Pharmacy price~€18–35 / pack

Your schedule is personal

These are typical steps only. Your doctor adjusts the plan to how you respond and tolerate it — and you can message them at any point.

Safety first

Safety, in full.

Sildenafil is an effective medicine — and like any medicine it carries risks. Your doctor screens for all of this before prescribing. Here's the honest picture, not just reassurance.

Prescribed for adult men with erectile dysfunction. Taken about 30–60 minutes before sexual activity.

Standard starting dose is 50 mg taken on demand, no more than once per day.
Effect lasts up to 4 hours; sexual stimulation is still required for the medicine to work.
A heavy or fatty meal can delay onset — taking it on a lighter stomach gives a more predictable response.

Who should not take it

You take any nitrate medicine (for chest pain / angina) or amyl-nitrite recreational drugs (“poppers”) — combination can cause life-threatening blood-pressure drops.
You take riociguat (for pulmonary hypertension) or any other guanylate-cyclase stimulator.
Recent heart attack, stroke or unstable angina in the last 6 months.
Severe liver impairment, severe low blood pressure, or known hereditary degenerative retinal disorders.
You have ever had non-arteritic ischaemic optic neuropathy (NAION).

When to seek urgent care

For severe, sudden or unexpected symptoms, call your local emergency number or go to the nearest emergency department. Then let your doctor know through your account chat.

Read the full Sildenafil safety summary

PRICING

One price. No surprises.

€25 per online medical consultation. If the doctor does not approve treatment, we refund you in full within 48 hours.

SINGLE CONSULTATION

What our patients say.

Verified reviews from Hi-Doctor patients · names changed for privacy · individual results vary.

Discreet from start to finish. The questionnaire was thorough and the doctor adjusted my dose after feedback.

Daniel P.

3 months in treatment

They checked my heart medication before prescribing — that level of care is why I stayed.

Sergio L.

7 months in treatment

Asking questions through the private chat was easy, and the answers came from the actual doctor.

Andreas W.

4 months in treatment

FREQUENTLY ASKED QUESTIONS

Questions about Sildenafil.

Find out if it's right for you

See if Sildenafil is appropriate for you.

Answer a few questions and a licensed EU doctor reviews your case within 24 hours. Refunded in full if it's not right for you.

Start consultation · €25 See Sexual health

OTHER SEXUAL HEALTH TREATMENTS

Explore related treatments.

Viagrasildenafil Tadalafil Cialistadalafil Vardenafil Levitravardenafil Avanafil Spedraavanafil Stendraavanafil

Sildenafil is a selective PDE-5 inhibitor EMA-approved for erectile dysfunction in adult men.

PDE-5 inhibitorOral tablet · on-demand actionEMA-approvedPrescription-only

WHAT IT IS

Selective phosphodiesterase-5 inhibitor.

Sildenafil is the active ingredient in Viagra and many generics authorised in the EU. It belongs to the PDE-5 inhibitor family alongside tadalafil, vardenafil and avanafil. Each molecule differs in onset, duration and selectivity over secondary receptors.

Its effect is facilitatory, not inductive: it requires sexual stimulation to produce a response — it does not cause an erection on its own.

HOW IT WORKS

Cavernosal vasodilation via nitric oxide.

During sexual stimulation, the nervous system releases nitric oxide in erectile tissue. Nitric oxide activates guanylate cyclase, raising cGMP levels and relaxing the smooth muscle of penile arteries, increasing blood flow.

Sildenafil blocks PDE-5, the enzyme that degrades cGMP. By inhibiting it, cGMP stays elevated longer and the erectile response is prolonged.

Onset of action is 30–60 minutes after intake; duration is 4–6 hours. Absorption is slowed by fatty meals.

WHO IS A CANDIDATE

Indication and ruling out cardiovascular causes.

The EMA indication is for adult men with erectile dysfunction. The licensed doctor reviews your cardiovascular history, current medication and risk factors. Erectile dysfunction is often an early marker of subclinical cardiovascular disease — ruling that out is part of the evaluation.

It is contraindicated with nitrates (severe hypotension risk), riociguat and specific antiretroviral combinations. The questionnaire is designed to flag these cases.

WHAT TO EXPECT

On-demand dosing and tolerance.

Sildenafil is taken on demand, about an hour before planned sexual activity. The standard starting dose is 50 mg, adjustable to 25 or 100 mg based on response and tolerance. It should not be taken more than once a day.

In studies, satisfactory clinical response exceeds 70 % in adequately selected patients — the outcome depends on the underlying cause, the dose, and concurrent cardiovascular factors.

SAFETY

Side effects, contraindications and interactions.

The most common side effects are headache, facial flushing, nasal congestion, dyspepsia and transient visual changes (light sensitivity, blue-tinged perception).

Absolute contraindications include concomitant nitrates (nitroglycerin, isosorbide), a history of NAION (non-arteritic anterior ischaemic optic neuropathy) and specific riociguat combinations. The doctor reviews the full questionnaire before prescribing.

Seek emergency care if you experience chest pain, priapism (erection > 4 h) or sudden vision loss.

REVIEWED BY HI-DOCTOR LICENSED PHYSICIANS · EDUCATIONAL CONTENT, NOT A SUBSTITUTE FOR A CONSULTATION

ALSO AVAILABLE IN

The Sildenafil consultation works the same way across the EU.

AVAILABLE ACROSS SPAIN