While it's always preferable to titrate, you can certainly start them quickly, and at least some people can tolerate coming back off them quickly (for a case study, see Oliver Sacks' account of Witty Ticcy Ray, who took haldol during the week for his tourettes and
took breaks on weekends). And
some people do get zyprexa
as a prn for when they start cycling. The folks over at crazymeds have a pretty good handle on it, and can explain the pharmacodynamics if you care to take a look.