Green’s Dictionary of Slang

go-fast n.

also go-faster
[its effects]

(drugs) methcathinone.

[[Aus]Age (Melbourne) 9 Apr. 14/2: It is known that the ‘go-fast’ drug coramine has been found in swabs taken from both Tarien and Cromis].
[US]Abel Dict. Drug Abuse Terms n.p.: go-faster.
[Aus]R.G. Barrett Between the Devlin 109: [T]ough, hard men with probably a bit of ‘go fast’ running through their systems.
[US]J. Wambaugh Finnegan’s Week 151: I can let you have a quarter a go-fast for twenny bucks.
[NZ]D. Looser ‘Boob Jargon’ in NZEJ 13 29: go fast n. Speed, an amphetamine drug.
[US]ONDCP Street Terms 10: Go-fast — Methcathinone; crank; methamphetamine.
[NZ]D. Looser Boobslang [U. Canterbury D.Phil. thesis] 79/2: go-fast n. speed .

In compounds

go-fast pills (n.)

(Aus. drugs) any form of chemical stimulant, esp. used for horses.

[Aus]Sport (Adelaide) 19 Sept. 7/3: There is nothing in what the papers wanted us to look upon as a sensation. If some go-fast pills were mentioned in the plot, then I’d say there might be something in it.
[Aus]Braidwood Dispatch (NSW) 12 Aug. 3/3: ‘Brad’ [...] went to the pack in his mixed [doubles]. [...] After he had par taken of a double handful of go-fast pills he quickly sparkled and was enabled to see the day out.
[Aus]Baker Aus. Lang. (2nd edn) 213: [...] go-fast pills.
[Aus]P. Doyle (con. late 1950s) Amaze Your Friends (2019) 94: [H]ow about some go-faster pills?’ ‘For the horse?’ ‘For me, for Christ’s sake’.