Green’s Dictionary of Slang

1. the teeth.

1963–74

B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 38: You swallow as many prawns as you can without closing the old pearly gates.

2. (drugs) LSD [the drug can offer visions of heaven, i.e. the ‘pearly gates’].

1971		Chronicle-Telegram (Elyria, OH) 16 Mar. 2/7–8: The chart [...] describes LSD as ‘pearly gates,’ ‘heavenly blue’ and ‘wedding bells.’.
1982		AS LVII:4 289: A sampling of current names for varieties of LSD would include peace, pearly gates, serenity [etc.].
2001		ONDCP Street Terms 16: Pearly gates — LSD.