Abbreviation for the pharmeceutical named Quaalude. It was used in the 1960s and 1970s as an anxiolytic, for the treatment of insomnia, and as a sedative. It became highly popular for recreational use in the 1980's, particularly in California. The active ingredient is Methaqualone, a depressant which is now a schedule 1 substance in the United States. It is still available for prescription in Canada.
"Hey man you alright?"
"Yeah just a little on edge."
"Hey man sorry I was so out of it last night, someone slipped me a bad lude."