A combination of the erectile dysfunction drug Viagra and the popular raver drug Ecstasy, sextacy sounds too good to be true: warm gooey feelings combined with a raging hardon sounds like it can't do much beyond ruin normal sex for you forever.
Which is exactly the problem, as this combination can potentially lead to permanent impotence.
The trouble starts when said raging hardon just won't go away, even after ejaculation. If both drugs are taken at the same time, this means you could be looking at an erection that will last anywhere from four to six hours. This, incidentally, is a bad thing, since priapism can cause blood clots which may permanently damage the penis's ability to become erect.
Basically, if you're really gung-ho about sex on ex but just can't get it up otherwise, make sure you wait until you're near the end of your roll before taking your little blue friend.