A "4 Bar" is one of the street names for the prescription drug Alprazolam. The more popular or trade/company name for the drug is Xanex. Medically it is used to treat anxiety disorders and panic attacks. "It works by decreasing excitement in the brain"www.nlm.nih.gov" The name "4 bar" is derived from the appearance of the pill witch is scored into four sections. Xanex is usually white, while some generic versions can be yellow. The high last around 4 hours, so experienced users sometimes take more than one. The drug is highly addictive if abused.
"Man, I just popped two 4 bars and I'm feelin loaded"

"Now it's six Xanex just to feel right" -- Rick Ross
by Professor Jdotdunn July 18, 2010
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zanex... a medication used for people with multiple personality disorder however people who do not have this disorder and take them will experience a feeling of severe drunkedness, memory loss, and sleep
damn i took those 4-bars last night and now i have no fuckin idea what happened
by shitdamn May 17, 2005
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