Green’s Dictionary of Slang

Nixon n.

[the corruption of US President Richard M. Nixon (1913–94)]

(drugs) inferior marijuana sold fraudulently as being of high quality.

1969
19691970197119721973197419751976
1977
[US]R.R. Lingeman Drugs from A to Z (1970).
[US]Smith & Gay Heroin in Perspective 204: Nixon. Low quality or ‘shitty’ street dope.
[US]S.N. Pradhan Drug Abuse in Spears (1986).