Cialis stays in your system for up to 36 hours and may provide support for erections during that entire time. Summary Cialis and Viagra are both pills for treating erectile dysfunction. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Trimazosin Other Interactions Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. The products discussed in this site may have different product labeling in different countries. Your healthcare provider can help you determine the right dosage for you.Strengths: 25 mg, 50 mg, mg; Brand: Viagra. 50 mg, mg; Adult dosage (ages 18–64 years) Typical dosage: 50 mg, taken as needed about 1 hour before sexual activity. It can be taken Both Viagra and sildenafil are available in mg, mg, and mg doses. REX MD currently has a out of 5-star rating on Trustpilot as of November About 84% of the over 3, reviews. Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash.