(California, US, qualifier:African-American Vernacular, slang) To get high from the drug MDMA (Ecstasy).
Similarly, some members of the Bay's black community, who feel that goin' dumb isn't particularly smart, have compared thizzin' (taking Ecstasy) to the crack epidemic. 2006 July, Erick K. Arnold, “Dumbed Down”, in Vibe: