Green’s Dictionary of Slang

(US) a drastically slowed-down movement, sometimes locked on the same spot, exhibited in a mental patient experiencing the effects of the tranquilizers thorazine or largactil.

1976		J.A. Bockar Primer for the Nonmedical Psychotherapist 73: This [slowed-movement] is mockingly referred to by chronic knowledgeable patients as the ‘Thorazine shuffle’.
1984		M. MacPherson Long Time Passing xi: Doc tors [...] numbed them with damaging ThorAzine, known to [Vietnam War] veterans as ‘gorilla biscuits’, which turned them into slow-moving and stumbling zombies. Veterans caustically called it the ‘Thorazine shuffle’.
1992		M. Sprouse Sabotage in the Amer. Workplace 158: If someone is given Thorazine for a long time, it affects their central nervous system. Anybody coming to our ward would see lots of people shuffling around. They called it the Thorazine shuffle.
1998		A. Devlin Invisible Women 264: [The] ‘Largactil shuffl’e’ or, even more cruelly , ‘muppet shuffle’ - have become part of the prison lexicon .
2003		D. Kent Snake Pits 108: Many walk with an awkward, dragging gait nicknamed "the Thorazine shuffle.
2006		B. Matthews Intractable [ebook] [T]he Largactil shuffle [...] where prisoners were in a constant state of sedation and shuffled around aimlessly in their drug-induced stupor.
2011		W. Henderson City of Nightmares Part Two 1: Some were just walking in place, which was called the Throzine [sic] shuffle.