Yes, Molly's meaning is the same as Mary's. But if you really want you could make up your own...such as "One who overdosed on prescription drugs." :-P
Mollies are a type of fish...ooh, here's something:
(from dictionary.com) Molly Maguire (m[.a]*gw[imac]r"); pl. Molly Maguires (-gw[imac]rz). (a) A member of a secret association formed among the tenantry in Ireland about 1843, principally for the purpose of intimidating law officers and preventing the service of legal writs. Its members disguised themselves in the dress of women. (b) A member of a similar association of Irishmen organized in the anthracite coal region of Pennsylvania, about 1854, for the purpose of intimidating employers and officers of the law, and for avenging themselves by murder on persons obnoxious to them. The society was broken up by criminal prosecutions in 1876.
Maybe you'd be better off sticking with Mary's meaning. :D