It works by helping to relax blood vessels in the penis, allowing blood to flow in to the penis leading to an erection. If you intend to use Cialis, you should take it 20-30 minutes before planned sexual activity. An erection is achievable for upward to 36 hours after taking it (this means the ability to have an erection may last this long, however the real erections will only keep going for a normal period of time). It may also be taken as a daily low dose pill. Does Cialis have side effects? The particular most common side effects with Cialis include: head ache, indigestion, back pain, muscle aches, flushed skin, rigid or runny nose. These types of side effects usually go away after a that same day. Very occasionally, Cialis can result in a painful erection or an erection that won’t go away. If this happens, and the erection lasts for more than 4 hours, you should Buy Cialis 5 mg go to the nearest emergency department. Prolonged erections can be dangerous.