Cialis vs. The dose of CIALIS for use as needed should be limited to 10 mg no more than once every 72 hours in patients taking potent inhibitors of CYP3A4 such as ritonavir, ketoconazole, and itraconazole [see Drug Interactions 7. Tadalafil was administered to over men during clinical trials worldwide. Stepwise increase in alpha-blocker dose may be associated with further lowering of blood pressure when taking a PDE5 inhibitor. Your healthcare provider can help you determine the right dosage for you. Both Cialis and Viagra work in this way.Cialis comes in several different strengths, including: milligrams (mg) 5 mg. 10 mg. 20 mg. The cost for these different strengths depends on whether you have insurance, your individual plan. Cialis (tadalafil) is an oral medication that treats erectile dysfunction (ED). One dose of Cialis lasts longer than a dose of the well-known Viagra (sildenafil). You can take Cialis when you need it, typically 30 minutes before sex. If that doesn’t work for you, another option is taking a low-dose pill every day for ongoing erectile support. Questions and Answers about Viagra, Levitra, Cialis, and Revatio: Possible Sudden Hearing Loss Regulatory History for Cialis from Drugs@FDA Historical Information.