Medicines that block an enzyme called CYP3A4. This information is reviewed by a licensed practitioner who will assess your eligibility for the medication. Levitra vardenafil : This medication is taken one hour before sex and can last up to 24 hours. Those with pre-existing conditions should always consult a healthcare provider before taking new medications or supplements. Insurance can help you save even more on consultations and medications. Other warning signs of an unsafe online pharmacy include outdated medication, no customer service, or suspiciously low prices. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines.Cialis can cost around $ to $ per month out of pocket, depending on the dosage you need. The first generic version of Cialis was released in October , and other . Tadalafil (Cialis). This medication is taken with or without food an hour before sex. It works for up to 36 hours. You can take it in a small dose daily or in a larger dose as needed. . You can opt to have your prescription sent to a local pharmacy (generic or name brand) or use.