Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Tadalafil can be synthesized starting from D – tryptophan methyl ester and piperonal via a Pictet—Spengler reaction. If you become pregnant while taking tadalafil, call your doctor. Summary Cialis and Viagra are both pills for treating erectile dysfunction. There are two different ways to take tadalafil, either daily or on an as needed basis. Both Cialis and Viagra work in this way.Side Effects. Headache, stomach upset, back pain, muscle pain, stuffy nose, flushing, or dizziness may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. To. Here are some details about tadalafil: Learn more about the different dosages for Cialis here. Pros and cons at a glance Below are some advantages and . Cialis: mg, 5 mg, 10 mg, and 20 mg, taken as needed The cost of the medication is from $ per month for Cialis and from $40 per month for tadalafil. Online consultations are free of charge.