I saw on another subreddit a user had claimed that speed was used during the war, by an unnamed nation(s), to help increase soldier's alertness while in the trenches.
Immediately my BS alarms were going off, I do a decent amount of reading on the BEF and I've never seen that claim come up. Did any nations actually issue "speed" to their troops in WWI? And if they did, was it actually to increase alertness in the trenches? Or was my initial gut reaction correct?
Can you link to where you saw this? /u/commiespaceinvader has written about the use of methamphetamine in World War II, but I can find no mention of its use in WWI, and from what I did find, it doesn't seem that it was even commercially viable until after that war had ended.
/u/Georgy_K_Zhukov has already linked my previous answer on the topic but while amphetamine was discovered in 1887 and methamphetamine in 1919, no commercial production existed until 1934 in the US resp. 1938 in Germany. Hence, its use for troops in WWI seems doubtful to the point of being able to dismiss right out of hand. The most likely explanation is that above mentioned redditor mixed up WWI and WWII.
Edit: Also here is a more extensive answer of mine on drug use in WWII.