Green’s Dictionary of Slang

1. describing a narcotic that has been adulterated with milk of magnesia.

1935

A.J. Pollock Und. Speaks 20/1: Chalked up, morphine, heroin or cocaine that has been adulterated with milk of magnesia.

2. under the influence of cocaine.

1955		H. Braddy ‘Narcotic Argot Along the Mexican Border’ in AS XXX:2 86: CHALKED UP, part. adj. phr. ‘High’ on cocaine.
2001		ONDCP Street Terms 5: Chalked up — Under the influence of cocaine.