In trials investigating Cialis, the majority of participants receiving the drug experienced a significant improvement in ED and maintained an erection. You may take this medicine with or without food. Take tadalafil at around the same time every day. Ask your doctor if you are not sure whether any of your medications contain nitrates. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately or get emergency medical treatment, and avoid sexual activity until your doctor tells you otherwise. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health.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 . Is a mg dose of Cialis safe to take? No, 40 milligrams (mg) is not a safe dose of Cialis to take. The maximum recommended dosage of Cialis is 20 mg once per . Efficacy Dosing Guidelines Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as .