Green’s Dictionary of Slang

(drugs) barbiturates.

1968		‘Sl. of Watts’ in Current Sl. III:2 46: Stumblers n. Barbiturates (Drug users’ jargon).
1971		E.E. Landy Underground Dict. (1972) 179: stum [...] Sleeping pill.
1972		E. Folb Urban Black Argot 145: Stoms / Stums / Stumblers barbiturates, particularly ‘Seconal’.
1980		E. Folb Runnin’ Down Some Lines 167: Dem stums git you so messed up you be fallin’ on yo’ ass!
2001		ONDCP Street Terms 20: Stumbler — Depressants.