Erectile Dysfunction · Clinical Information
Erectile Dysfunction Medications
Pharmacist-reviewed information on Sildenafil, Viagra, and Tadalafil — three licensed PDE5 inhibitor treatments for erectile dysfunction, available following a clinical assessment.
UK Pharmacist Reviewed
UK Licensed
GPhC Registered Pharmacy
Medication 01
Prescription Only
UK Licensed
Sildenafil
sildenafil citrate
PDE5Inhibitor
What it is
Sildenafil is the generic form of Viagra and the most widely prescribed treatment for erectile dysfunction. It is clinically identical to the branded version but available at a lower cost.
How it works
Sildenafil inhibits the enzyme PDE5, which restricts blood flow to the penis. By blocking PDE5, it allows the blood vessels to relax and widen, enabling a firm erection in response to sexual stimulation.
Effectiveness
Up to 82% of men report improved erections in clinical trials. Onset is typically 30 to 60 minutes after taking the tablet, with effects lasting up to 4 to 6 hours.
Dosing
Taken as needed, approximately 30 to 60 minutes before sexual activity. Available strengths:
25 mg
50 mg
100 mg
50 mg is the standard starting dose. Maximum one tablet per 24 hours.
Who it is for
Adult men with erectile dysfunction who are in good cardiovascular health. Suitable for on-demand use when sexual activity is anticipated. Works best when taken on an empty stomach or after a light meal.
Side effects
- Headache and facial flushing (most common)
- Indigestion and nasal congestion
- Visual disturbances such as mild colour tint or sensitivity to light
- Dizziness, particularly when standing up quickly
Not suitable if
You are taking nitrate medicines (e.g. GTN spray), have severely reduced blood pressure, have had a recent heart attack or stroke, or have severe liver or kidney impairment.
Medication 02
Prescription Only
Original Brand
UK Licensed
Viagra
sildenafil citrate
PDE5Inhibitor
What it is
Viagra is the original branded sildenafil, manufactured by Pfizer and the world's most recognised treatment for erectile dysfunction. It contains the same active ingredient as generic sildenafil.
How it works
Identical mechanism to sildenafil — blocks PDE5 to relax penile blood vessels and increase blood flow, producing an erection in response to natural sexual stimulation. No sexual stimulation, no effect.
Effectiveness
Up to 82% of men achieve improved erections. As the originator product, Viagra underwent the pivotal clinical trials that established efficacy data for all sildenafil treatments.
Dosing
Taken as needed, approximately 30 to 60 minutes before sexual activity. Available strengths:
25 mg
50 mg
100 mg
50 mg is the standard starting dose. Maximum one tablet per 24 hours.
Who it is for
Adult men with erectile dysfunction who prefer the reassurance of the original branded product. Clinically equivalent to generic sildenafil but preferred by some patients for confidence and familiarity.
Side effects
- Headache and facial flushing (most common)
- Indigestion and nasal congestion
- Visual disturbances such as mild colour tint or sensitivity to light
- Dizziness, particularly when standing up quickly
Not suitable if
You are taking nitrate medicines (e.g. GTN spray), have severely reduced blood pressure, have had a recent heart attack or stroke, or have severe liver or kidney impairment.
Medication 03
Prescription Only
UK Licensed
Tadalafil
tadalafil
Long-ActingPDE5 Inhibitor
What it is
Tadalafil is the generic form of Cialis and is known as the "weekend pill" due to its exceptionally long duration of action — up to 36 hours — giving far greater spontaneity than shorter-acting alternatives.
How it works
Like sildenafil, tadalafil inhibits PDE5 to increase blood flow to the penis. Its unique molecular structure gives it a much longer half-life, meaning it remains active in the body for up to 36 hours after a single dose.
Effectiveness
Up to 81% of men report successful erections. Onset is typically within 30 minutes, with effects lasting up to 36 hours — significantly longer than sildenafil's 4 to 6 hour window.
Dosing
Two treatment options available — as needed or daily use:
2.5 mg
5 mg
10 mg
20 mg
10 mg as needed or 2.5–5 mg once daily. Daily dosing removes the need to plan around activity.
Who it is for
Adult men with erectile dysfunction who want greater spontaneity, or those who prefer a daily tablet rather than taking medication before each episode of sexual activity. Also licensed for benign prostatic hyperplasia (BPH).
Side effects
- Headache and back pain (more common than with sildenafil)
- Muscle aches, particularly in the lower back and limbs
- Indigestion and nasal congestion
- Flushing and dizziness
Not suitable if
You are taking nitrate medicines (e.g. GTN spray), alpha-blockers, or drugs that affect CYP3A4 liver enzymes. Not recommended with severe liver or kidney impairment, or uncontrolled blood pressure.
Side-by-Side Comparison
| Sildenafil | Viagra | Tadalafil | |
|---|---|---|---|
| Drug class | PDE5 Inhibitor | PDE5 Inhibitor | Long-Acting PDE5 Inhibitor |
| Active ingredient | Sildenafil citrate | Sildenafil citrate | Tadalafil |
| Brand or generic | Generic | Original brand (Pfizer) | Generic (Cialis original) |
| Onset of action | 30 – 60 minutes | 30 – 60 minutes | 30 minutes |
| Duration of action | 4 – 6 hours | 4 – 6 hours | Up to 36 hours |
| Standard dose | 50 mg as needed | 50 mg as needed | 10 mg as needed or 5 mg daily |
| Available strengths | 25 mg, 50 mg, 100 mg | 25 mg, 50 mg, 100 mg | 2.5 mg, 5 mg, 10 mg, 20 mg |
| Daily use option | No | No | Yes — 2.5 or 5 mg |
| Effectiveness | Up to 82% | Up to 82% | Up to 81% |
| Food interaction | Reduced by fatty meals | Reduced by fatty meals | Minimal — food does not affect absorption |
| UK licensed | Yes | Yes | Yes |
Clinical Disclaimer
This page is for informational purposes only and does not constitute medical advice. All prescriptions are issued following a clinical assessment by a UK-registered pharmacist prescriber. These medications are not suitable for everyone — particularly those taking nitrate medicines or with significant cardiovascular conditions. Always read the patient information leaflet. If you experience a prolonged erection lasting more than 4 hours, chest pain, or sudden vision or hearing loss, seek immediate medical attention or call 999.
