Deathsticks are a serum, usually distributed in glass tubes – to consume, the user simply ingests the contents, which are bright red or yellow in colour (the different colours are purely cosmetic and have no different effects).
Taking Deathsticks is quite popular among a certain class of people living not quite as long a time ago in a galaxy far, far away: among other effects, it deadens the user’s connection to the Force, which can be desirable to those who want no part of the endless Sith-Jedi struggles.
It is a potent hallucination, which makes it easier to dismiss any Force-ghosts one might see as mere hallucinations. As the name suggests, however, taking it tends to shorten one’s lifespan not inconsiderably.