I was writing a short story about a soldier in the battle of trebia (gave up ain't planning to finish it) and i wanted to include something about what drugs they used, how they used it and what the latin name would be
In case you didn't see it there's a big topic about opium in ancient Rome going on now: https://www.reddit.com/r/AskHistorians/comments/dy20t9/marcus_aurelius_one_of_the_five_good_emperors_and/
Similar questions have been asked before, but none that I can see directly related to life in the military. However, these other threads may still give you the details you're looking for.
Overall, recreational drug use during the Roman period was mostly limited to alcohol, though opium became trendy among the wealthy at various points.