Retail therapy was first used as a term in the 1980s with the first reference being this sentence in the Chicago Tribune of Christmas Eve 1986. "We've become a nation measuring out our lives in shopping bags and nursing our psychic ills through retail therapy." (2)
In 2001, the European Union conducted a study finding that 33% of shoppers surveyed had "high level of addiction to rash or unnecessary consumption'." This was causing debt problems for many with the problem being particularly bad in Scottish young people.
Researchers at Melbourne University have advocated its classification as a psychological disorder called oniomania or compulsive shopping disorder.
Retail therapy need not be a negative term. It can be a neutral term that describes the pleasures of the total shopping experience, used by many people to boost their mood. Shopping as a way of boosting one's mood does not necessarily involve rash or inadvisable purchases. Retailers may view the entertainment aspect of their stores as a means of boosting store traffic, so that some of those customers make purchases, but not necessarily inappropriate or inadvisable ones.
Retail addiction or shopping addiction should be considered a separate and serious problem. The term "therapy" by definition implies a treatment for a problem (here, depression or stress), not a problem itself. Retail therapy may be the wrong treatment in many cases, but it is not, by definition, dangerous or problematic.
(1) Oxford English Dictionary Online "Retail therapy" accessed 20 March 2006
(2) Oxford English Dictionary Ibid