It's interesting to note that by taking ephedrine you actually
create what is called bladder outlet obstruction (BOO), i.e. ephedrine is an antagonist of alpha-blockers. Whereas alpha-blockers relax the bladder outlet (the internal sphincter) ephedrine constricts it. People with BPH (enlarged prostate) already have BOO, so ephedrine might exacerbate it and cause complete obstruction (inability to void).
Cancer is not associated with effy, however prostate enlargement is. Read above.
iNTERSTINGLY, yohimbine, which is an alkaloid classified as an alpha-2-andrenergic blocking agent.