How Long Does Cialis Last? How long varies with the drug. Viagra and Levitra take about 30 minutes to work, and the effects last for about 4 hours after you take the pill. You should take Cialis at least 2 hours before you plan to have sex. The effects may last for up to 36 hours after you take it. Which Is Better Viagra or Cialis? Cialis (tadalafil) and Viagra (sildenafil) are phosphodiesterase-5 (PDE5) inhibitors used for treating impotence (erectile dysfunction, or ED). ... Cialis provides penile hardness (the ability to obtain an erection) over a longer period than Viagra because it lasts up to 18 hours, while Viagra only lasts for about 4 to 6.