Rarely reported side effects include: an erection that will not go away priapism. Remove the cap by pushing it down and twisting it counter-clockwise. Keep out of the reach of children. If you have an erection that lasts more than 4 hours, get medical help right away. By controlling the enzyme, sildenafil helps to maintain an erection after the penis is stroked.What Is Viagra? Viagra (sildenafil) was the first erectile dysfunction pill the FDA approved, back in Like Cialis, it’s a PDE5 inhibitor that increases blood flow to the penis. The difference is that the effects of Viagra don’t last very long (only about four to six hours). Viagra is always taken before an anticipated sexual activity. Viagra can be taken 30 minutes before sex, while Levitra should be taken 1 hour before. Side effects include stuffy or runny nose, headaches, vision changes, dizziness, flushing, and back pain. AdWith RexMD you’re saving time and money with our Viagra delivery. Get started now. Reliable E.D. meds prescribed by real doctors. Get your free & private online visit has been visited by 10K+ users in the past monthFree Shipping · Discreet Packaging · Personalized Plan · Real DoctorsTypes: Hair Loss · Premature Ejaculation · Sexual Health · Privacy Policy.