We rely on peer-reviewed studies, academic research institutions, and medical associations. Medicines that block an enzyme called CYP3A4. Do not take vardenafil more than once a day. Extended duration of efficacy of vardenafil when taken 8 hours before intercourse: a randomized, double-blind, placebo-controlled study. These medicines are called PDE5 inhibitors.2 rows · Levitra does have fewer common side effects than Viagra, and it’s not associated with. What are the side effects of Levitra (Vardenafil)? Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or. Common side effects of Levitra include: facial flushing (reddening), headaches, stomach upset, diarrhea, flu-like symptoms, and; nausea. Serious side effects of Levitra include: .