Definition: Priapism is an erection that will not go down and lasts for hours. The Viagra and Cialis labels describe it as a painful erection over 6 hours and say an erection lasting more than 4 hours needs emergency care, because untreated priapism can permanently damage the penis.
Both PDE5 inhibitor labels say erections lasting more than 4 hours and priapism have been reported. Viagra calls them infrequent and Cialis calls them rare. The Viagra label (section 5.2) adds that caution is used in people with:
The 4-hour mark on the labels is the point to get emergency care, not the 6-hour mark used in the description. Waiting raises the chance of lasting damage, so the label tells you to act before it reaches the full definition. The Caverject label draws the same line: it counts erections of 4 to 6 hours as prolonged erections and those of 6 hours or more as priapism.
If it happens, the time you took the medicine and how much are the first things a clinician will ask. A log entry with the dose and time answers that quickly. Priapism is a listed warning for PDE5 inhibitors and appears on some other labels on this site, such as Caverject, which is injected into the penis. In the Caverject trials, erections of 4 to 6 hours occurred in 4% of men.
Read more on Dose Track: Viagra side effects · Cialis side effects · Caverject side effects