slang shortening of quaalude, by 1973.
lude (lōōd)
n.
A pill or tablet that contains the drug methaqualone.
Quaalude2, a depressant drug; any methaqualone capsule or pill: Only this year ''ludes'' (Quaaludes or ''downs'') were the hot sellers/ Dropping the Last 'Lude (1960s+ Narcotics)