Younger people might do well treated with tadalafil, (Cialis) while older people with other health issues might be better off using sildenafil (Viagra) or vardenafil (Levitra) but more data are needed. Do not take more than 1 tablet a day. Your doctor may increase or decrease your dose, depending on how well it works and how often you take it. The effects may last longer than 24 hours, so you're not recommended to take the 10mg or 20mg tablets every day.