Green’s Dictionary of Slang

(US drugs) heroin.

2001		ONDCP Street Terms 14: Manteca (Spanish) — Heroin.
c.2003		Frank M. Figueroa ‘What The Soneros Are Saying’ at Picadillo.com 🌐 Here are a few additional drug-related terms that you may find in song lyrics: manteca – marihuana, cocaine.