Green’s Dictionary of Slang

(US drugs) a powerful variety of heroin.

2017		D. Winslow Force [ebook] ‘I'll save you the trouble of counting,’ Pena says. ‘One hundred kilos even. Mexican cinnamon heroin’.
2019		D. Winslow Border [ebook] Heroin even evolves to get fitter. First there was Mexican black. Then cinnamon. Then fire.