Xanax and the benzodiazepines
Xanax, and its family of drugs, the benzodiazepines (or “benzos”), are quite good at slowing the brain down. They do this by activating the GABA inhibitor pathways. This produces a feeling of calm, good will, and relaxation.
As such, they are quite popular, both as prescription medication, and as drugs of abuse. This is unfortunate, as the benzos are both highly addictive and extremely difficult to quit. If you stop abruptly, withdrawal can be so bad as to send you into convulsions or make you go temporarily insane.
Yowch.