Green’s Dictionary of Slang

(drugs) non-proprietary capsules of barbiturate powder sold on the black market and with implication of having been made up on the US/Mexico border.

1971		E.E. Landy Underground Dict. (1972).
1980		E. Folb Runnin’ Down Some Lines 230: borders, border reds Noncommercially compounded capsules of secobarbital or other barbiturate compounds encased in red capsules.