When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. If you are taking tadalafil for erectile dysfunction, your doctor will probably start you on an average dose of tadalafil and increase or decrease your dose depending on your response to the medication. If you are taking tadalafil for erectile dysfunction on a regular schedule, take the missed dose as soon as you remember it. Nitrates come as tablets, sublingual under the tongue tablets, sprays, patches, pastes, and ointments. For this purpose, one dose works for up to 72 hours. What side effects can this medication cause? Do not take a double dose to make up for a missed one. · Cialis (tadalafil) is prescribed to treat erectile dysfunction and symptoms of benign prostatic hyperplasia. It comes as a tablet that’s taken as needed or once per . Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) . Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged .