Cognitive impairment as a predictor of long-term psychological distress in patients with polysubstance use disorders: a prospective longitudinal cohort study.

"Declarations Ethics approval and consent to participateThis study protocol was reviewed and approved by the Regional Ethics Committee West, University of Bergen, approval reference REK 2011/1877. The research was conducted according to its guidelines and those of the Helsinki Declaration (1975). All participants gave written informed consent. Consent for publicationNot applicable. Competing interestsThe authors declare no competing interests. Competing interests The authors declare no competing interests."

"Funding Open access funding provided by University of Bergen. The Western Norway Regional Health Authority, Strategic Initiative for Substance Use Research [912003], and the Department of Research and Education, Division of Psychiatry, Stavanger University Hospital funded this research."