Don't expect Cialis to work instantly - plan for up to 2 hours for full effect. You still need sexual stimulation for Cialis to give you a strong erection. Taking it daily lets you be ready anytime, but can build up in your system. Discontinuing Cialis does not cause withdrawal symptoms, and it is safe to stop taking it at any time. However, your symptoms will likely return when you no longer take the drug. If you experience any severe side effects, stop taking his medication immediately and seek urgent medical help.