Tadalafil (Generic Cialis®) Erectile Dysfunction, (Impotence), is the persistent inability to achieve and maintain an erection sufficient to complete sexual intercourse. Tadalafil is taken orally as needed prior to sexual activity (about one hour before is most effective). Tadalafil works along with sexual stimulation to help achieve an erection. Your results may vary, but for some men, Cialis® (tadalafil) often works within 30 minutes and stays effective for up to 36 hours.