British researchers say that users of a potent strain of marijuana nicknamed "skunk" were 18 times more likely to have suffered a psychotic episode than other marijuana users, the BBC reported July 2.

However, the researchers also noted that evidence on the link between psychosis and marijuana use has been inconsistent. Lead researcher Maria Di Forte of the Institute of Psychiatry at King's College London said that confusion had been sown by studying cannabis users as a homogenous group rather than teasing out subclassifications such as the type of drug used.

Di Forte and colleagues also found that marijuana users who had experienced a psychotic episode were twice as likely to be long-term users and three times more likely to be daily users.

Fellow researcher Paul Morrison said that the higher levels of THC in "skunk" may trigger psychosis, and he noted that "skunk" also has lower levels of cannabidiol, which may protect users from the effects of THC.