> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hi-doctor.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Sildenafil (Viagra)

> Sildenafil, authorised across the EU since 1998, relaxes penile blood vessels so more blood flows in on stimulation — mechanism, dosing and side effects.

Sildenafil is a prescription tablet for erectile dysfunction, first authorised across the EU on 13 September 1998. It relaxes the blood vessels in the penis so more blood can flow in when you are sexually aroused — it does not create arousal on its own, so sexual stimulation is still needed for it to work.

<Info>
  Active ingredient: sildenafil · Dosages: 25 / 50 / 100 mg on demand · Onset: 30–60 minutes · Effect window: around 4–6 hours.
</Info>

## Can I get it?

Yes, if a doctor decides it is right for you. Sildenafil is authorised in the EU and can be prescribed after a medical review of your cardiovascular health, current medication and contraindications.

## What it is

Sildenafil is a phosphodiesterase-5 (PDE5) inhibitor, taken by mouth, for adult men with erectile dysfunction. It does not cause spontaneous erections or change desire — sexual stimulation is still required.

## How it works

<CardGroup cols={3}>
  <Card title="Arousal releases nitric oxide" icon="bolt">
    During sexual stimulation, nerves and blood vessel linings in the penis release a gas called nitric oxide, which switches on an enzyme, guanylate cyclase, making a messenger chemical called cyclic GMP inside the erectile tissue.
  </Card>

  <Card title="Cyclic GMP lets blood in" icon="droplet">
    Cyclic GMP relaxes the smooth muscle in the corpus cavernosum, the two spongy columns that run the length of the penis. As that muscle relaxes, blood flows in faster than it drains away, and the penis becomes firm.
  </Card>

  <Card title="Sildenafil blocks the PDE5 enzyme" icon="lock">
    PDE5 normally ends an erection by breaking down cyclic GMP. Sildenafil blocks it, so the blood vessels stay relaxed for longer when there is sexual stimulation.
  </Card>
</CardGroup>

## What the studies reported

| Source                                                                                        | Evidence                                  |
| --------------------------------------------------------------------------------------------- | ----------------------------------------- |
| EMA EPAR — Viagra (sildenafil), EMEA/H/C/000202                                               | Marketing authorisation issued 13/09/1998 |
| EMA — Viagra EPAR product information (SmPC sections 4.2, 4.8, 5.1)                           | Regulatory reference                      |
| *N Engl J Med* 1998 — Oral sildenafil in the treatment of erectile dysfunction (PMID 9580646) | Peer-reviewed                             |

<Note>
  Both pivotal studies were short — 12 and 24 weeks — and relied on self-reported questionnaires and diaries, so they describe short-term effect rather than long-term outcomes.
</Note>

## Who it is not suitable for

Sildenafil is contraindicated in men taking nitrate medicines or nitric-oxide donors, because the combination can cause a serious drop in blood pressure. It is also contraindicated in men who have already lost vision in one eye from NAION. The doctor reviews cardiovascular health before prescribing; men with severe cardiovascular disease may not be suitable. A dedicated study found mild, temporary blue/green colour-discrimination changes 1 hour after a 100 mg dose, with no effect remaining 2 hours after the dose.

## What has been reported

| Effect                                                | Frequency (EU product information)                             |
| ----------------------------------------------------- | -------------------------------------------------------------- |
| Headache, flushing, dyspepsia                         | Very common (≥1 in 10) — 6% to 18% of men in the pivotal trial |
| Nasal congestion                                      | Common (1 in 100 to 1 in 10)                                   |
| Visual disturbance, colour distortion, blurred vision | Common (1 in 100 to 1 in 10)                                   |
| NAION — sudden vision loss in one eye                 | Rare (1 in 10,000 to 1 in 1,000)                               |

<Warning>
  Sildenafil is contraindicated with nitrate medicines and nitric-oxide donors, because the combination can cause a serious drop in blood pressure. It is also contraindicated in men who have already lost vision in one eye from NAION.
</Warning>

## Taking it day to day

<CardGroup cols={2}>
  <Card title="Timing" icon="clock">
    Take it 30–60 minutes before sexual activity.
  </Card>

  <Card title="Food" icon="utensils">
    Avoid heavy, high-fat meals right before — they delay onset.
  </Card>

  <Card title="Nitrates" icon="triangle-exclamation">
    Never combine with nitrates or poppers.
  </Card>

  <Card title="Adjusting the dose" icon="sliders">
    Message your doctor to adjust the dose if needed, rather than exceeding one dose in 24 hours.
  </Card>
</CardGroup>

Practical day-to-day guidance — storage, and what to do if the medication is not working — is covered in the [sildenafil treatment guide](https://hi-doctor.ai/guides/sildenafil).

## Common questions

<AccordionGroup>
  <Accordion title="How long does sildenafil take to work?">
    Sildenafil takes 30 to 60 minutes to start working. The effect lasts around 4 to 6 hours. Sexual stimulation is required — it does not cause an automatic erection.
  </Accordion>

  <Accordion title="Can I drink alcohol with sildenafil?">
    The EU product information advises that alcohol can worsen dizziness and erectile difficulty. Avoid excess alcohol when taking sildenafil.
  </Accordion>

  <Accordion title="What happens if I take sildenafil with nitrates?">
    Sildenafil is contraindicated with nitrate medicines and nitric-oxide donors because the combination can cause a serious drop in blood pressure. This includes poppers (amyl nitrite). Never combine them.
  </Accordion>

  <Accordion title="Can sildenafil cause vision problems?">
    Visual disturbance, colour distortion and blurred vision are listed as common in the EU product information. A dedicated study found mild, temporary blue/green colour-discrimination changes 1 hour after a 100 mg dose, with no effect after 2 hours. Sudden vision loss in one eye (NAION) is rare.
  </Accordion>

  <Accordion title="How should I take sildenafil for the best effect?">
    Take one tablet 30 to 60 minutes before sexual activity. Avoid a heavy, high-fat meal right before — it delays onset. Do not take more than one dose in 24 hours. If the dose is not right, message your doctor rather than increasing it yourself.
  </Accordion>

  <Accordion title="Is sildenafil authorised in the EU?">
    Yes. Sildenafil has been authorised across the EU since 13 September 1998 (EMA EPAR Viagra, EMEA/H/C/000202), so a licensed doctor can prescribe it when clinically appropriate.
  </Accordion>
</AccordionGroup>

## How Hi-Doctor handles it

A licensed doctor reviews every sexual health option and recommends what fits your history and goals. See [how the consultation works](/essentials/how-it-works) and [how we handle safety and eligibility](/essentials/safety). Pricing is on [the pricing page](/essentials/pricing). For a related concern, see [premature ejaculation](/library/conditions/premature-ejaculation) or [dapoxetine](/library/medicines/dapoxetine).

## Start a consultation

<Card title="Sexual health consultation" icon="stethoscope" href="https://hi-doctor.ai/consultation/sexual-health/1">
  Answer the sexual health questionnaire and a registered doctor reviews it.
  They decide whether treatment is appropriate, which one, and at what dose —
  and declining is a normal outcome. See [what it costs](/essentials/pricing)
  and [how the review works](/essentials/how-it-works).
</Card>

<Warning>
  This page is reference information, not medical advice and not a prescription. Whether a medicine is appropriate for you is decided by a registered doctor after reviewing your consultation.
</Warning>