Viagra vs Cialis vs Levitra vs Stendra: Which ED Medication Is Right for You?
A complete comparison of onset, duration, side effects, interactions and how to choose.
Part of the Access Doctor Erectile Dysfunction guide.
Key fact: All four MHRA-approved ED medications 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.
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success rate for sildenafil (Viagra) in clinical trials
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 | 30–60 min | 4–6 hours | Yes — avoid fatty meals | Most widely known; generic equivalent available |
| Levitra / Vardenafil | Vardenafil | 25–60 min | 4–6 hours | Mild | May work slightly faster in some men; QT prolongation caution |
| 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 | Minimal | Fastest onset; ~100× more PDE5-selective; branded only |
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) | Visual disturbances more common than others (temporary blue tinge, altered colour discrimination) |
| Tadalafil (Cialis) | Back pain and muscle aches due to longer systemic presence |
| Vardenafil (Levitra) | QT prolongation risk — do not use with certain cardiac medications; contraindicated in long QT syndrome |
| Avanafil (Spedra) | Generally well tolerated; headache and flushing most common |
Seek emergency care if you experience an erection lasting more than 4 hours (priapism), sudden vision loss, or sudden hearing loss after taking any ED medication.
Important Interactions — All Four Medications
- Nitrate medicines (glyceryl trinitrate, isosorbide mononitrate) — absolute contraindication; dangerous blood pressure drop
- 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; dose adjustment may be required
Frequently Asked Questions
What is the difference between Viagra, Cialis, Levitra, and Stendra?
All four are PDE5 inhibitors. Key differences are duration: Viagra (4–6 hours), Levitra (4–6 hours), Spedra (up to 6 hours), Cialis (up to 36 hours). Spedra has the fastest onset at 15–30 minutes.
Which ED medication is most effective?
All four have comparable efficacy: sildenafil ~82%, tadalafil ~81%, vardenafil ~80%, avanafil ~77%. Choice is based on lifestyle preference, not efficacy.
Can I drink alcohol with ED medication?
Small amounts are generally acceptable. Larger quantities can impair erections and worsen dizziness. Grapefruit juice should be avoided with all four.
Are ED medications safe with heart conditions?
PDE5 inhibitors must not be combined with nitrates (for angina). If you have a heart condition, your prescriber will assess whether ED medication is appropriate.
Do I need a prescription for Viagra in the UK?
Since 2017, sildenafil 50mg (Viagra Connect) is available without a full prescription at UK pharmacies. For all doses and brands, a prescriber consultation via Access Doctor is the safest route.
Which ED medication lasts the longest?
Tadalafil (Cialis) — up to 36 hours. Also available as a once-daily 5mg dose for continuous management.
References
- National Institute for Health and Care Excellence (NICE). Erectile dysfunction: Clinical Knowledge Summary. Updated 2023. cks.nice.org.uk/topics/erectile-dysfunction
- NHS. Erectile dysfunction (impotence). nhs.uk/conditions/erection-problems-erectile-dysfunction
- Hatzimouratidis K et al. EAU guidelines on erectile dysfunction. Eur Urol. 2010;57(5):804–814. PubMed: 20388436
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. ED treatments are prescription-only medicines requiring clinical assessment. In a medical emergency, call 999.