It is not known if the medicine is safe for use in these patients. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects. Follow your doctor’s orders or the directions on the label. The products discussed in this site may have different product labeling in different countries. These medicines are called PDE5 inhibitors.VIAGRA can cause your blood pressure to drop suddenly to an unsafe level if taken with certain other medicines. Do not take VIAGRA if you take any other medicines called “nitrates.” Nitrates are used to treat chest pain (angina). A sudden drop in blood pressure can cause you to feel dizzy, faint, or have a heart attack or stroke.  · Generic Viagra is also available through Hims starting at $4 per dose. which belongs to a class of phosphodiesterase type 5 (PDE5) inhibitors. Viagra is the well-known brand-name version of. Rarely reported side effects include: an erection that will not go away (priapism). If you have an erection that lasts more than 4 hours, get medical help right away. If it is not treated right away, priapism can permanently damage your penis. sudden vision loss in one or both eyes.