The allegation that Accutane is somehow linked to suicidal thoughts and behavior has largely been a sideshow compared with the birth defect risks associated with the popular acne med, but it has lingered for nearly a decade. And this morning, US District Court Judge James Moody, who is overseeing multi-district litigation filed in Florida, ruled that Emory University Douglas Bremner psychiatry professor can testify as an expert witness for the plaintiffs. Why does this matter?

“This is significant because it’s the first time that he’ll be appearing at trial and introducing evidence - brain scans he conducted - that indicate the drug is linked to suicide,” says Mike Ryan, an attorney who has filed most of the two dozen or more Accutane suicide lawsuits around the country, which are mostly in Florida and New Jersey. Bremner’s appearance “was a hotly contested issue and this validates what the plaintiffs have been saying.” (You can read a recent motion by clicking on this).

Bremner first became involved in the issue when he was contacted by an Irish accountant, Liam Grant, whose son committed suicide while on Accutane. Frustrated by Roche, which first sold the brand-name version (there are several generics), Grant took the unusual step of funding Bremner’s research, which involved giving 28 patients brain scans and psychological tests that ruled out any connection between their acne and depressed feelings.

For four months, the patients received either Accutane or an antibiotic. New scans conducted on the group afterward showed the Accutane patients had decreased activity in an area of the brain thought to be involved with regulating mood. “What we can say is that Accutane affects brain function,” he told USA Today in 2005, “…and the areas that are affected are the areas involved with depression.”

A Roche spokeswoman wrote that the drugmaker doesn’t comment on litigation.