Both Cialis and Viagra work in this way. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. National Library of Medicine. The body takes longer to absorb it after a high-fat meal or alcohol. In some cases, ED can cause a strain on relationships and impact self-esteem. This increase in blood flow results in a firmer, longer-lasting erection.Cialis and Viagra have both been shown to be safe and effective for erectile dysfunction. The main differences are cost and timing. For occasional use, most people start with Viagra which also tends to be cheaper. Cialis lasts longer and can also be taken daily at a . You need a prescription to get Cialis, which you can acquire through your doctor or telehealth sources. Online ordering can be a great alternative if you prefer the convenience and discretion. avanafil (Stendra) sildenafil (Viagra) tadalafil (Cialis) vardenafil (Levitra, Staxyn) Caution: Do not use these ED medications if you take nitrates, such as nitroglycerin or a similar.