Definitely not poison

You conjure a perfectly brewed cup of magical coffee. Careful hot.

One willing creature can spend 1 minute drinking it and gain 1d8 to its initiative rolls and also choose to re-roll 1 attack or saving throw.

Additionally after the next long rest the consumer must roll a dc 10+1 wisdom save for each consecutive day it spends drinking the addictive brew. 
On a save nothing happens, on a fail the target has a -2 to intelligence, wisdom and charisma saves until the consume another cup of coffee.