The driver, whose name has not been released, was arrested and taken to a hospital for treatment of unspecified injuries.
Police said the man was unconscious and had overdosed on a drug, possibly heroin.
He regained consciousness when he was loaded into an ambulance and attempted to jump out and flee, but police caught him and restrained him with handcuffs.
Some patients at Gateway House said the driver had once been treated at the Vine Street halfway house.
No other injuries were reported.