Recent heart or blood vessel problems. It can also interact with many medicines, particularly nitrates used in some types of heart disease and blood pressure medicines. Oral medicines for ED usually work well and cause few side effects. Who should not take Cialis? What if I am taking other drugs?Find the best tadalafil or cialis prices near you now with our cost comparison tool and start saving today. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. The most commonly reported side effects in patients treated with Cialis during the testing of the product were: headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who.