Viagra vs Cialis vs Levitra vs Spedra: Which ED Medication Is Right for You?
A complete comparison of onset, duration, side effects, interactions and how to choose.
When to get urgent help: Call 999 if you get chest pain during or after sex (tell the paramedics which ED medicine you have taken, as nitrates such as GTN must not be given), or signs of a serious allergic reaction. Go to A&E straight away if an erection is painful or lasts more than 2 hours (do not drive yourself). Stop the medicine and get medical help straight away if you have a sudden decrease or loss of vision or hearing. See your GP about new erection problems, as they can be an early sign of heart disease or diabetes.
Part of the Access Doctor Erectile Dysfunction guide.
Key fact: All four MHRA-licensed ED tablets are PDE5 inhibitors that work through the same mechanism. They differ in how quickly they work, how long they last, and their side effect profiles. None produces an erection without sexual stimulation.
If you're trying to decide between the available options, this guide compares the four licensed ED medications side by side. For those who have already identified Cialis as the preferred option based on its longer duration, you can request branded Cialis through Access Doctor following a confidential consultation with a UK-registered prescriber. If you prefer a shorter-acting, cost-effective option for planned use, sildenafil (generic Viagra) is also available via the same consultation process, as are branded Viagra tablets.
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how long sildenafil (Viagra) usually works for
36 hrs
maximum duration of tadalafil (Cialis) — the longest of the four
15–30
minutes onset for avanafil (Spedra) — the fastest of the four
How PDE5 Inhibitors Work
All four medications inhibit an enzyme called phosphodiesterase type 5 (PDE5), which regulates blood flow in the penis. By blocking PDE5, they allow smooth muscle in penile blood vessels to relax more easily when sexually stimulated, enabling increased blood flow into the erectile tissue and facilitating an erection.
Important: PDE5 inhibitors do not cause erections on their own — sexual stimulation is still required. They enhance the body’s natural erectile response, not bypass it.
Comparison of All Four ED Medications
| Medication | Active ingredient | Onset | Duration | Food effect | Key notes |
|---|---|---|---|---|---|
| Viagra / Sildenafil | Sildenafil | About 1 hour (from about 30 min) | About 4 hours | Yes — a heavy meal can delay it | Most widely known; generic sildenafil available |
| Levitra / Vardenafil | Vardenafil | 25–60 min | Up to 4–5 hours | A high-fat meal can delay it | Can affect heart rhythm (QT interval) — not suitable for everyone |
| Cialis / Tadalafil | Tadalafil | ~30 min | Up to 36 hours | No | ‘Weekend pill’; 5mg daily option available; dual BPH licence |
| Spedra / Avanafil | Avanafil | 15–30 min | Up to 6 hours | A high-fat meal can delay it | Can start working the fastest |
Side Effects
As all four are PDE5 inhibitors, their common side effect profiles are similar: headache, facial flushing, nasal congestion, indigestion, and dizziness. Notable differences by medication:
| Medication | Notable side effects |
|---|---|
| Sildenafil (Viagra) | Changes in vision are more often reported (a temporary blue tinge or blurred vision) |
| Tadalafil (Cialis) | Back pain and muscle aches are more common |
| Vardenafil (Levitra) | Can affect heart rhythm (QT interval) — avoid if you have long QT syndrome or take certain heart rhythm medicines |
| Avanafil (Spedra) | Generally well tolerated; headache and flushing most common |
Get urgent help if an erection is painful or lasts more than 2 hours (go to A&E straight away), or if you get chest pain during or after sex (call 999). If you have a sudden decrease or loss of vision or hearing after taking any ED medicine, stop taking it and get medical help straight away.
Important Interactions — All Four Medications
- Nitrate medicines (GTN spray, tablets or patches; isosorbide mononitrate or dinitrate), nicorandil and “poppers” — never take together; dangerous blood pressure drop
- Riociguat (for high blood pressure in the lungs) — never take together
- Other ED medicines — do not take two ED medicines together
- Alpha-blockers (for prostate or blood pressure) — additive hypotensive effect; dose adjustment may be required
- Antihypertensives — additive blood pressure lowering; discuss with prescriber
- Grapefruit juice — inhibits drug metabolism; avoid with all four
- CYP3A4 inhibitors (certain antibiotics such as clarithromycin; antifungals such as ketoconazole) — increase drug levels; some combinations must be avoided and others need a lower dose
UK safety and prescribing information
- Legal status: most ED medicines are prescription-only medicines (POM) in the UK. The exceptions are Viagra Connect 50mg and tadalafil 10mg sold as a pharmacy medicine (such as Cialis Together), which men aged 18 and over can buy after a consultation with a pharmacist. Access Doctor supplies MHRA-licensed UK medicines, dispensed by our GPhC-registered pharmacy (#9011198) only after a prescriber has assessed your consultation. It is illegal to sell or supply prescription-only medicines without a prescription in the UK.
- Maximum dose: take no more than one dose of any ED medicine in 24 hours, and never take two ED medicines together.
- Driving: these medicines can cause dizziness and, with some, changes in vision. Check how they affect you before driving or using machinery.
- NHS: in England and Scotland, your GP can prescribe generic sildenafil or generic tadalafil on the NHS for erectile dysfunction if it is suitable for you. Branded Viagra and Cialis are only prescribed on the NHS in limited circumstances. In Wales, NHS prescribing of ED medicines, including generics, is currently limited to men who meet certain criteria, and the rules may differ in Northern Ireland, so ask your GP. NHS prescription charges apply in England unless you are exempt; prescriptions are free in Scotland, Wales and Northern Ireland.
Frequently Asked Questions
What is the difference between Viagra, Cialis, Levitra and Spedra?
All four are PDE5 inhibitors that help you get an erection when you are sexually aroused. The main difference is how long they last: Viagra about 4 hours, Levitra up to 4 to 5 hours, Spedra up to 6 hours and Cialis up to 36 hours. Spedra can start working the fastest, from about 15 to 30 minutes.
Which ED medication is most effective?
Studies suggest they work about as well as each other for most men. The best choice depends on how long you want it to last, how food affects it, side effects and your other medicines, so your prescriber will help you choose.
Can I drink alcohol with ED medication?
Small amounts are generally fine. Drinking a lot can make it harder to get an erection and can make dizziness worse. Avoid grapefruit juice, which can raise the levels of these medicines in your blood.
Are ED medications safe with heart conditions?
None of these medicines can be taken with nitrates, nicorandil or poppers, as this can cause a dangerous drop in blood pressure. If you have a heart condition, your prescriber will check whether ED medicine is safe for you.
Do I need a prescription for Viagra in the UK?
Viagra Connect 50mg is a pharmacy medicine that men aged 18 and over can buy after a consultation with a pharmacist. Other Viagra tablets and generic sildenafil need a prescription, as do Levitra and Spedra and most tadalafil. The exception for tadalafil is the 10mg strength sold as a pharmacy medicine, such as Cialis Together.
Which ED medication lasts the longest?
Tadalafil (Cialis) — one dose can work for up to 36 hours. It is also available as a lower dose taken once a day.
References
- National Institute for Health and Care Excellence (NICE). Clinical Knowledge Summaries: Erectile dysfunction. cks.nice.org.uk
- NHS. Erectile dysfunction (impotence). nhs.uk
- NHS. Sildenafil (Viagra). nhs.uk
- NHS. Tadalafil (Cialis). nhs.uk
- Electronic Medicines Compendium. Summaries of Product Characteristics for sildenafil, tadalafil, vardenafil and avanafil. medicines.org.uk
- Hatzimouratidis K et al. EAU guidelines on erectile dysfunction. Eur Urol. 2010;57(5):804–814. PubMed: 20388436
- Medicines and Healthcare products Regulatory Agency. Yellow Card scheme: report a suspected side effect or a fake medicine. yellowcard.mhra.gov.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Most ED medicines are prescription-only medicines (Viagra Connect 50mg and tadalafil 10mg sold as a pharmacy medicine are the exceptions), and they need a clinical or pharmacist assessment before they can be supplied. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
Reporting side effects: If you think a medicine has caused a side effect, you can report it to the MHRA through the Yellow Card scheme at yellowcard.mhra.gov.uk or the Yellow Card app. You can also report suspected fake or unlicensed medicines. Reporting helps keep medicines safe for everyone in the UK.