All four licensed PDE5 inhibitors in the UK block the same enzyme, allowing blood vessels in the penis to relax and fill in response to arousal. None creates arousal; all require it.
Choosing between them is a practical question about how they fit your life, not a question of which is strongest.
Sildenafil
- Onset: 30–60 minutes
- Duration: around 4–5 hours
- Food: significantly affected — a fatty meal delays it noticeably
- Doses: 25mg, 50mg, 100mg
- Availability: generic and inexpensive; 50mg available over the counter as Viagra Connect after a pharmacist consultation
The default first choice for most people, on cost and familiarity. Slightly more associated with visual effects — a blue tinge or light sensitivity — because of action on a related enzyme in the retina.
Tadalafil
- Onset: 30–60 minutes
- Duration: up to around 36 hours
- Food: minimally affected
- Doses: 2.5mg and 5mg for daily use; 10mg and 20mg as needed
- Availability: generic; 10mg available over the counter as Cialis Together after a pharmacist consultation
The long duration is the distinguishing feature, and for many people the decisive one — it removes the timing pressure that makes the whole thing feel clinical. The low daily dose is a different proposition again: continuous rather than event-driven. More associated with back and muscle pain than the others.
Vardenafil
- Onset: 25–60 minutes
- Duration: around 4–5 hours
- Food: affected, though somewhat less than sildenafil
- Doses: 5mg, 10mg, 20mg — more potent per milligram, so the numbers are not comparable with sildenafil's
- Availability: prescription only, generally dearer and stocked by fewer suppliers
Less visual disturbance than sildenafil. Mainly used when sildenafil has been tried properly and has not suited.
Avanafil
- Onset: around 15–30 minutes — the fastest of the four
- Duration: around 6 hours
- Food: relatively little effect
- Doses: 50mg, 100mg, 200mg
- Availability: prescription only, and typically the most expensive
The newest of the four and the most selective for PDE5, which in principle means fewer off-target effects. The speed of onset is its genuine selling point.
Which to Try
- Cost is the priority: generic sildenafil
- You dislike planning around a tablet: tadalafil, either as needed or as a low daily dose
- You want the shortest wait: avanafil
- Sildenafil caused visual effects or did not suit: vardenafil or avanafil
Response is individual. Failing on one does not predict failing on another, which is the main clinical argument for trying a different molecule rather than simply increasing the dose.
The Rule That Applies to All Four
None of them may be taken with nitrates — GTN spray, isosorbide mononitrate and similar — or with recreational poppers. The combined effect on blood pressure can be fatal. This is not a cautious warning; it is the reason a pharmacist asks about heart medication before selling you anything.
On NHS Availability
Generic sildenafil can be prescribed on the NHS for men with erectile dysfunction. Branded sildenafil, tadalafil, vardenafil and avanafil are restricted to particular circumstances. In practice that makes sildenafil the NHS default and the others a private cost for most people — which is worth factoring in before choosing on onset time alone.