Substance Abuse News

Young adults who have used cannabis or marijuana for a longer period of time appear more likely to have hallucinations or delusions or to meet criteria for psychosis, according to a report posted online today that will appear in the May print issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

Previous studies have identified an association between cannabis use and psychosis, according to background information in the article. However, concerns remain that this research has not adequately accounted for confounding variables.

Cannabis Use and Psychotic Outcomes

John McGrath, M.D., Ph.D., F.R.A.N.Z.C.P., of the Queensland Brain Institute, University of Queensland, Australia, and colleagues studied 3,801 young adults born between 1981 and 1984. At a 21-year follow-up, when participants were an average age of 20.1, they were asked about cannabis use in recent years and assessed using several measures of psychotic outcomes (including a diagnostic interview, an inventory of delusions and items identifying the presence of hallucinations).

At the 21-year follow-up, 17.7 percent reported using cannabis for three or fewer years, 16.2 percent for four to five years and 14.3 percent for six or more years. Overall, 65 study participants received a diagnosis of “non-affective psychosis,” such as schizophrenia, and 233 had at least one positive item for hallucination on the diagnostic interview.

Among all the participants, a longer duration since the first time they used cannabis was associated with multiple psychosis-related outcomes. “Compared with those who had never used cannabis, young adults who had six or more years since first use of cannabis (i.e., who commenced use when around 15 years or younger) were twice as likely to develop a non-affective psychosis and were four times as likely to have high scores on the Peters et al Delusions Inventory [a measure of delusion],” the authors write. “There was a ‘dose-response’ relationship between the variables of interest: the longer the duration since first cannabis use, the higher the risk of psychosis-related outcomes.”

Not a Simple Connection

In addition, the researchers assessed the association between cannabis use and psychotic symptoms among a subgroup of 228 sibling pairs. The association persisted in this subgroup, “thus reducing the likelihood that the association was due to unmeasured shared genetic and/or environmental influences,” the authors continue.

“The nature of the relationship between psychosis and cannabis use is by no means simple,” they write. Individuals who had experienced hallucinations early in life were more likely to have used cannabis longer and to use it more frequently. “This demonstrates the complexity of the relationship: those individuals who were vulnerable to psychosis (i.e., those who had isolated psychotic symptoms) were more likely to commence cannabis use, which could then subsequently contribute to an increased risk of conversion to a non-affective psychotic disorder.”

The findings should encourage further research to elucidate the mechanisms underlying the relationship between psychosis and cannabis use, the authors conclude.

Exposure to ecstasy or cocaine during adolescence increases the “reinforcing effects” that make people vulnerable to developing an addiction. This is the main conclusion of a research team from the University of Valencia (UV), which has shown for the first time how these changes persist into adulthood.

“Although MDMA and cocaine are psychoactive substances frequently used by teenagers, very few studies have been done to analyse the short and long-term consequences of joint exposure to these drugs”, José Miñarro, lead author of the study and coordinator of the Psychobiology of Drug Addiction group at the UV, tells SINC.

Long Lasting Changes

The study, published in the journal Addiction Biology, shows for the first time that exposure to these drugs during adolescence leads to long-lasting changes that increase the reinforcing power of ecstasy or MDMA, and which last until adulthood.

Miñarro’s team studied the joint consumption of different drugs in order to carry out an in-depth examination into the effects of this interaction. The scientists administered MDMA, cocaine and saline solution to mice over an eight-day period. “The animals exhibited an increase in vulnerability to re-establishing behaviour (relapse), showing a preference for certain environments previously associated with the pleasant effects of the drug”, explains Miñarro.

The results highlight that the so-called “reinforcing effects” are greater in adult mice treated with ecstasy or cocaine during adolescence than in adolescent mice not exposed to these drugs. “Adolescence is a critical stage in development, during which time drug consumption affects plastic cerebral processes in ways that cause changes that persist right through to adulthood”, adds the scientist.

Adolescence Polyconsumption

The results of various surveys, both national and international, show that one of the most common patterns of drug use is polyconsumption. Ecstasy is regularly consumed alongside other drugs such as alcohol, cannabis and cocaine. These same surveys show that 44% of cocaine users in Spain also take ecstasy, and this consumption takes place primarily during adolescence.

The State Study on Drug Use among Secondary School Students (ESTUDES 2007, Government Delegation for the National Plan on Drugs), showed that more than 75% of secondary school students who reported taking MDMA also said they used cocaine, while only 44.3% of cocaine users said they took ecstasy.