Geronimo, n. — Green’s Dictionary of Slang

Geronimo n.

[it leads one to excesses, supposedly similar to those of an Apache warrior]

(drugs) a mixture of alcohol and barbiturates.

1950		Time 28 Aug. 4: A goof ball is a...Geronimo...or any other barbiturate sleeping pill [HDAS].
1969		R.R. Lingeman Drugs from A to Z (1970).
1977		Wesson & Smith Barbiturates 122: Geronimo. Alcohol mixed with barbiturates.