Lysergic acid diethylamide ( or or ), abbreviated
LSD or
LSD-25, also known as
lysergide (
INN) and colloquially as
acid, is a
psychedelic drug of the
ergoline family, well known for its psychological effects—which can include altered thinking processes, closed- and open-eye visuals,
synesthesia, an altered
sense of time, and
spiritual experiences—as well as for its key role in
1960s counterculture. It is used mainly as an
entheogen and
recreational drug. LSD is not
addictive. However, acute adverse psychiatric reactions such as anxiety, paranoia, and delusions are possible.