Many many many times throughout the Star Wars movies, games, books, ect... the mention of death sticks appears. In Star Wars II: The Attack of the Clones Obi-Wan is asked to buy some from a shady alien in the bar when they are chasing Zam. As far as I can figure out they are a type of drug. However specifically, does anyone know what they do to you? Make you hallucinate, are they a relaxer, do they just make you feel really good? I am curious.
The aptly named 'Death Stick' is a mild hallucinogen developed by the Collective Commerce District (CoCo) medical facilities. They are highly addictive and the cilona extract shortens the users lifespan with each successive dose.
As well as offering a warped version of reality and making bright lights dance to the beat of Coruscant night club music they are unique in that they reduce the individuals connection with the force, making this guy possibly the dumbest drug dealer in the galaxy (he also tried selling Rancor nail blades to Jango Fett not two days earlier).
Death Sticks are taken either by mixing with a drink, intravenous injection or by smoking the more potent granulated variety. Treatment for addiction can be found at any good medical centre but it can be very expensive.
Source: Star wars wikia: Death Stick