Sildenafil (Viagra) and tadalafil (Cialis) are both PDE5 inhibitors approved by the MHRA for treating erectile dysfunction. They work in fundamentally the same way, but there are important practical differences that may make one a better fit for you.
Duration of Action
This is the single biggest difference between the two medications:
- Sildenafil — lasts approximately 4–6 hours
- Tadalafil — lasts up to 36 hours, earning it the nickname "the weekend pill"
Tadalafil's longer window can reduce the pressure of timing, allowing for more spontaneous sexual activity.
Onset Time
Both medications should be taken before sexual activity, but their onset differs:
- Sildenafil — typically works within 30–60 minutes
- Tadalafil — may take 30 minutes to 2 hours, though many men notice effects within 30 minutes
Food Interactions
Sildenafil is significantly affected by fatty food, which can delay absorption by up to an hour. Tadalafil is not meaningfully affected by food, making it more convenient if taken around mealtimes.
Side Effects
Both drugs share common side effects such as headache, flushing, nasal congestion, and indigestion. However:
- Sildenafil is more likely to cause temporary visual disturbances (blue-tinted vision)
- Tadalafil is more likely to cause back pain and muscle aches, particularly with the daily dose
Dosing Options
Sildenafil is taken as needed in 25 mg, 50 mg, or 100 mg doses. Tadalafil can be taken as needed (10 mg or 20 mg) or as a daily low dose (2.5 mg or 5 mg), which maintains a steady level in the body and allows for completely spontaneous activity.
Cost in the UK
Generic sildenafil is typically the cheapest ED medication in the UK, with tablets often available for under £1 each from GPhC-registered pharmacies. Generic tadalafil is slightly more expensive but still very affordable compared to branded alternatives.
Which Should You Choose?
If you prefer a lower cost and shorter-acting option, sildenafil is an excellent first choice. If you value spontaneity and a longer window, tadalafil — especially the daily dose — may suit you better. Your prescriber can help you decide based on your health profile and preferences.