Marijuana Linked With Depression?

There have been tons of studies done that link long-term marijuana use with different forms of mental illness. But, the effects of short-term marijuana use seem to have little to no effect at all. There is a new study however, that suggests that cannabis use could be associated with symptoms of depression, but only if the teens have a certain genetic trait.

The problems with this study are pretty lengthy; they used a small pool, the statistical analysis used in the study is rare, and the particular genetic trait that is implicated has been associated with a number of different behavioral traits. But the authors have validated some of the theories in their study with a second population, so it may be worth looking at.

The study’s authors suggest that there’s a history of research into the connection between depressive symptoms and the use of cannabis. The scientists then go on to suggest that it’s possible for cannabis to enable these symptoms, but only if the individuals involved have a certain genetic trait.

The Trait

They then test the genetic trait: a variation of the serotonin reuptake protein, which clears the neurotransmitter out of nerve synapses after signaling takes place. The gene is targeted by a variety of antidepressants so the scientists’ estimates aren’t unreasonable. But, other studies have tried and failed to suggest a link between this gene and cannabis use.

Despite the usually unfounded connection between this gene and marijuana, the scientists confidently wrote, “It is likely that the link between teenage drug abuse and depressive symptoms is conditional on the presence of the short allele of the 5HTTLPR polymorphism of the serotonin transporter gene.”

Normally, the standard approach at this point would be to take a large population and perform a diagnosis of depression, searching for the serotonin signaling genotype and finding out who uses cannabis. But, once again the authors were inconsistent with standard approaches. Instead, they decided to work with a small sample of Dutch families, did the genotyping, and tracked several teenagers over several years, performing surveys of marijuana use and behavior tendencies. Other factors were also considered, such as: alcohol and tobacco use, parental education, and skills.

By the end of the study, the participants had increased marijuana consumption from 10 percent to just under 40 percent, with about 17 percent of the teenagers becoming weekly users by the end of the study.

Taking the Study Seriously

Next, the authors performed an odd type of statistical analysis called parallel-process latent growth model, a method of testing whether the growth curves of two features follow similar trajectories. The authors describe it as “regressing the intercept and the slope of depressive symptoms on the intercept of cannabis use simultaneously.”

Despite the study’s interesting finds, there are just too many problems with the actual scientific approach of the study to take it seriously on its own. Maybe, if coupled with different scientific approaches and a larger pool of participants, the study could hold some merit.

ars technica Photo by : Samantha Cohen