Oral ED medicines might not work or might be dangerous if you also take any of the following:
Nitrate medicines. Often, these are prescribed for chest pain called angina. Some examples of nitrates are nitroglycerin (Nitro-Dur, Nitrostat, others), isosorbide mononitrate (Monoket) and isosorbide dinitrate (Bidil).
Alpha-blockers. These are commonly prescribed for an enlarged prostate or male pattern baldness. They include dutasteride (Avodart, Jalyn) and finasteride (Propecia, Proscar).
Medicines that block an enzyme called CYP3A4. These include itraconazole (Sporanox, Tolsura), ketoconazole (Extina, Ketozole, others) and ritonavir (Norvir).
Oral medicine for ED also might not be safe or work well if you have:
Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension.
Severe liver disease.
Kidney disease that needs to be treated with dialysis.
Recent heart or blood vessel problems. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months.
An inherited eye disease that affects the retina.
Kidney disease that needs to be treated with dialysis.