> ## 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.

# Tadalafil — 36-hour window, dosing and side effects

> Tadalafil 10/20mg is a PDE5 inhibitor authorised in the EU since 2002, with an effect lasting up to 36 hours. How it works, dosing and side effects.

Tadalafil is a prescription tablet for erectile dysfunction, authorised across the EU since 2002. Like sildenafil, it relaxes the blood vessels in the penis so blood can flow in — sexual arousal is still needed for it to work. Its distinguishing feature is how long the effect lasts: the EU product information reports a measurable effect up to 36 hours after a dose.

<Info>
  Active ingredient: **tadalafil**. Dosages: **10 / 20 mg on demand**, or **5 mg daily**.
</Info>

## What it is

A PDE5-inhibitor tablet taken by mouth, for adult men with erectile dysfunction. A daily low dose also eases prostate symptoms (lower urinary tract symptoms from BPH, an indication for which tadalafil is authorised) and it cannot be combined with nitrate heart medicines.

## How it works

<CardGroup cols={3}>
  <Card title="Arousal releases nitric oxide" icon="bolt">
    Sexual stimulation triggers the release of nitric oxide, which raises cGMP in the erectile tissue.
  </Card>

  <Card title="Tadalafil blocks the PDE5 enzyme" icon="lock">
    Tadalafil is a selective, reversible blocker of phosphodiesterase type 5 (PDE5), whose normal job is to break cGMP back down. With PDE5 blocked, cGMP builds up instead of being cleared away as fast as it appears.
  </Card>

  <Card title="Blood flows in, erection follows" icon="droplet">
    Higher cGMP relaxes the smooth muscle in the arteries of the corpus cavernosum, so blood flows into the penis and an erection can form. The same relaxation happens in the prostate and bladder, which is why a daily dose can also ease urinary symptoms.
  </Card>
</CardGroup>

## EU authorisation

Tadalafil has been authorised for use in the EU since **12 November 2002** (EMA EPAR — Cialis, EMEA/H/C/000436).

## What the studies reported

Integrated trial data pooled five 12-week manufacturer-run trials; the reported 7.9-point IIEF (erectile function score) change is the within-group change from baseline, not the difference from placebo. (*J Urol* 2002, PMID 12352386.)

## Dosing

<Tabs>
  <Tab title="On demand">
    One tablet — 10 mg or 20 mg — at least 30 minutes before sexual activity. Effect window: up to 36 hours.
  </Tab>

  <Tab title="Daily">
    A low 5 mg dose taken once every day. Reaches a steady effect in a few days, allowing spontaneity without planning around a dose.
  </Tab>
</Tabs>

## What has been reported

All of the following are listed as **common** (1 in 100 to 1 in 10 men) in the EU product information, with frequency generally rising at higher doses.

| Reaction                | EU SmPC frequency                                                            |
| ----------------------- | ---------------------------------------------------------------------------- |
| Headache                | Common — most headaches with once-daily dosing occur in the first 10–30 days |
| Back pain               | Common                                                                       |
| Myalgia (muscle pain)   | Common                                                                       |
| Dyspepsia (indigestion) | Common                                                                       |
| Flushing                | Common                                                                       |
| Nasal congestion        | Common                                                                       |

<AccordionGroup>
  <Accordion title="Non-arteritic anterior ischaemic optic neuropathy (NAION)">
    Contraindicated in men who have lost vision in one eye because of NAION, whether or not the episode was linked to a PDE5 inhibitor.
  </Accordion>

  <Accordion title="Use with nitrates">
    Contraindicated with nitrate medicines and with guanylate cyclase stimulators, and after a recent heart attack (within 3 months) or stroke (within 6 months). Nitrates and poppers are contraindicated: blood pressure can fall dangerously.
  </Accordion>

  <Accordion title="Erections lasting more than 4 hours">
    Seek emergency medical attention immediately for an erection lasting more than 4 hours, sudden vision loss, or chest pain.
  </Accordion>
</AccordionGroup>

## Storage

Store at room temperature below 25°C. Keep in the original packaging to protect from light and moisture. Do not use after the expiry date on the carton.

## What to expect

Most side effects are usually mild and temporary. Contact the doctor for persistent back pain or muscle aches; seek emergency care immediately for an erection lasting more than 4 hours, sudden vision or hearing changes, or chest pain.

## How Hi-Doctor handles it

A licensed doctor reviews every sexual-health case and recommends what fits the history and goals, weighing the on-demand versus daily approach with the patient. Medication is paid separately at a pharmacy; see [pricing](/essentials/pricing) for what the consultation fee covers.

## Sources

* EMA EPAR — Cialis (tadalafil), EMEA/H/C/000436, marketing authorisation issued 12/11/2002
* EMA — Cialis EPAR product information (SmPC sections 4.2, 4.8, 5.1)
* *J Urol* 2002 — Efficacy and safety of tadalafil: results of integrated analyses (PMID 12352386)

Further reading on hi-doctor.ai: the [tadalafil treatment guide](https://hi-doctor.ai/guides/tadalafil) covers day-to-day use in more detail.

## Related reading

* [Erectile dysfunction](/library/conditions/erectile-dysfunction) — what the doctor rules out first
* [Sildenafil](/library/medicines/sildenafil) — the shorter-acting PDE5 inhibitor a doctor may consider instead
* [Safety and eligibility](/essentials/safety)
* [How Hi-Doctor works](/essentials/how-it-works)

## 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>