Green’s Dictionary of Slang

(drugs) using or under the influence of injectable narcotics.

1953		E. Hunter ‘Vicious Circle’ in Jungle Kids (1967) 32: I ain’t been fixed since the Ice Age.
1963		M. Braly Shake Him Till He Rattles (1964) 121: You’re just not going to be happy until you get yourself fixed, are you?
1968–70		Current Sl. III–IV (Cumulation Issue).