An antidepressant thought to be effective in treating compulsive buying has yielded inconclusive results in a recent study, leaving researchers to suggest the disorder may have more complex biological roots than suspected.

The study, conducted by lead author Lorrin Koran, a professor of psychiatry and behavioral sciences at Stanford University in California, followed up a similar 2003 study that found people with compulsive-buying disorder improved when treated with antidepressants.

In the new study, which will be published in the April issue of the Journal of Clinical Psychopharmacology, some participants were given an antidepressant - the medication escitalopram - while others were given a placebo. Researchers found no difference in the relapse rate in both groups.

"It was a shock that, when we did the trial again with the active ingredient, it didn't work exactly the same way. It should have," Koran said in a release.

Trial size may have skewed outcome

He suggested that the small trial size of 17 participants may have influenced the outcome of the study. But, he noted, the disorder may have different biological manifestations.

"I don't think we're dealing with one pure biological disorder," Koran said in a release. "We're dealing with a behavior that has different biological roots in different people and therefore we may have had very different groups of people in the two studies."

Koran noted that people suffering from the disorder should not be discouraged by the inconclusive findings, reminding patients that many treatments have been successful.

The disorder, which has been likened to impulsive behaviours exhibited in pathological gambling, is characterized by a frequent and irresistible urge to buy unneeded items. Koran estimates that approximately six per cent of the U.S. population suffers with the disorder. Comparable Canadian statistics are not available.

Koran said researchers in future trials might perform imaging studies of patients' brains for different patterns and responses.

"We would look for a difference in the brain activation patterns of those who respond to the drug [versus] those who don't," Koran said.