Great question — answering as the UphillTech team:
A quick comparison of the canon listing for both "spice" and "coaxium" on Wookiepedia confirms that they are not the same thing. In canon, spice is a narcotic, and there are several types, but all are meant for human consumption. Coaxium only appears in the new Han Solo movie and upcoming book, and by all descriptions is completely different. http://starwars.wikia.com/wiki/Coaxium http://starwars.wikia.com/wiki/Spice
Full answer by Todd Wilcox: https://movies.stackexchange.com/a/89415 (CC BY-SA 4.0).
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