ED: The Basics — Erectile Dysfunction Explained
How erections work, what causes ED, MHRA-approved treatments, safe use and when to seek help.
Part of the Access Doctor Erectile Dysfunction guide.
Key fact: Erectile dysfunction (ED) affects approximately one in five men in the UK at some point in their lives. Despite its prevalence, many men delay seeking help — but MHRA-approved treatments are highly effective and available without a GP appointment.
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Start Consultation →How Does an Erection Work?
For an erection to occur, a specific sequence of events must happen in the right order. When a man is sexually stimulated (physically or psychologically), nerves in the penis release nitric oxide, which causes smooth muscle in the penile arteries to relax. This relaxation allows blood to flow into the two spongy chambers of the penis (the corpus cavernosum), which expand and create the firm erection. When sexual stimulation stops, or after orgasm, the process reverses.
Erectile dysfunction occurs when this process is disrupted at any point — whether due to insufficient blood flow, nerve damage, hormonal imbalance, or psychological factors. PDE5 inhibitors (sildenafil, tadalafil, vardenafil, avanafil) work by blocking the enzyme that breaks down the chemical signal keeping penile arteries relaxed, making it easier for the process to complete when sexually stimulated.
Main Treatment Options for ED
All four MHRA-approved ED medications are PDE5 inhibitors — they work by the same mechanism but differ in how quickly they work, how long the effect lasts, and whether they can be used daily.
| Medication | Active ingredient | Onset | Duration | Food effect? |
|---|---|---|---|---|
| Viagra / Sildenafil | Sildenafil | 30–60 min | 4–6 hours | Yes — avoid fatty meals |
| Cialis / Tadalafil | Tadalafil | 30 min | Up to 36 hours | No |
| Levitra / Vardenafil | Vardenafil | 25–60 min | 4–6 hours | Avoid fatty meals |
| Spedra / Avanafil | Avanafil | 15–30 min | Up to 6 hours | Minimal effect |
For a detailed comparison of all four, see our guide to Viagra vs Cialis vs Levitra vs Spedra. To choose between the two most commonly prescribed options, see Tadalafil vs Sildenafil.
Dosage and Safe Use
- Sildenafil (Viagra): standard starting dose is 50mg taken 30–60 minutes before sexual activity; available in 25mg, 50mg and 100mg
- Take on an empty stomach or after a light meal — a large, high-fat meal delays absorption
- Never take more than one tablet per day regardless of medication
- Avoid combining with nitrate medicines (used for chest pain) — this can cause a dangerous drop in blood pressure
- Avoid grapefruit juice, which affects how sildenafil and other PDE5 inhibitors are metabolised
- Avoid excessive alcohol — it can impair sexual function and worsen dizziness
Seek urgent medical attention if you experience: an erection lasting more than 4 hours (priapism — a medical emergency), sudden vision loss, sudden hearing loss, or chest pain after taking ED medication.
When to See a Doctor About ED
See a doctor if ED has been present for more than a few weeks, is causing significant distress, or if you have any underlying health conditions (heart disease, diabetes, hypertension) that may be contributing. ED can sometimes be an early warning sign of cardiovascular disease — new-onset ED in men over 40 should prompt a cardiovascular risk assessment.
For a detailed look at physical and psychological causes, see our guide to what causes erectile dysfunction.
Frequently Asked Questions
What is erectile dysfunction?
Erectile dysfunction (ED) — also called impotence — is the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual intercourse. It affects around one in five men in the UK at some point in their lives.
How does Viagra work for erectile dysfunction?
Viagra (sildenafil) is a PDE5 inhibitor. It relaxes the smooth muscle in penile blood vessel walls, increasing blood flow when sexually stimulated. Sexual stimulation is always required — it does not cause an erection automatically.
How long does Viagra take to work?
Viagra typically takes 30–60 minutes to work. For best results, take it on an empty stomach or after a light meal. Effects generally last 4–6 hours.
Can I take Viagra long-term?
Yes. Viagra has a well-established long-term safety profile. Regular prescriber review is recommended to ensure it remains appropriate for your circumstances.
Will Viagra affect my fertility or contraception?
Viagra has not been found to affect fertility in men or women and does not interfere with any form of contraception.
How do I get ED medication from Access Doctor?
Complete a short confidential online consultation. Our GPhC-registered pharmacist independent prescribers review your information and, if appropriate, issue a prescription for discreet next-day delivery.
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
- Shamloul R, Ghanem H. Erectile dysfunction. Lancet. 2013;381(9861):153–165. PubMed: 23040455
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.