If too much is used, the chance of side effects is increased. Cialis Daily tadalafil : This low-dose Cialis works by increasing blood flow to the penis over time, making it easier to have an erection when aroused. You may also wish to talk to students in those labs. Viagra is always taken as needed, usually about an hour before sex. Do not keep outdated medicine or medicine no longer needed.Financial assistance Next steps Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile dysfunction. The cost of the drug with and without insurance can depend on . It is typical for students to contact several labs at a time (and you may not hear back from each one). If you don’t hear back after your first email, send another email a week later. See also: Generic Viagra. Once you settle on a lab, you can begin your research. Some students choose to volunteer in the lab (anywhere from hours per. Headache, flushing, and upset stomach are common Viagra side effects. These effects are usually mild and often resolve on their own. While rare, Viagra can cause an erection that lasts longer than 4 hours (priapism). This can result in permanent damage if left untreated. Vision changes are also possible.