A new study fills this research gap by examining how cannabis use among teenagers is linked with hypomania in early adulthood.

The research was led by Dr. Steven Marwaha, a clinical academic psychiatrist from the University of Warwick in the United Kingdom, and the findings were published in the journal Schizophrenia Bulletin.

Dr. Marwaha and colleagues started out from the observation that despite the documented link between teenage marijuana use and psychiatric disorders, the prospective association between cannabis use and symptoms of bipolar disorder has been insufficiently investigated.

In fact, it has been found on several studies that the link between teenage cannabis use and psychiatric conditions. For instance, one study suggested that marijuana use causes changes in brain structure that are similar to those caused by schizophrenia.

Another study in rodents suggested that adolescent use of the drug may bring about schizophrenia symptoms, but only in those already genetically susceptible to the illness.

This study looked at the link between teenage use of cannabis and hypomania, which is a symptom that is often experienced by those with bipolar disorder. Hypomania is characterized by feelings of elation, intense excitement, reduced need for sleep, and hyperactivity.

Weekly cannabis use may cause hypomania

Dr. Marwaha and colleagues reviewed the data available on 3,370 participants from a U.K. birth cohort study called the Avon Longitudinal Study of Parents and Children.

The team examined the link between the use of cannabis at the age of 17 and the development of hypomania at ages 22–23.

Using regression analysis, the scientists adjusted for gender, alcohol and other drug use, early environmental risk factors — such as childhood adversity or abuse — and depression and psychosis at the age of 18.

The study also found that using cannabis at least two or three times per week was a strong predictor for hypomania in early adulthood.

The relationship between teenage cannabis use and hypomania depended on the dose, with weekly use being more strongly associated with the symptom than "any use."

The use of cannabis was also found to mediate the link between childhood sexual abuse and hypomania, as well as that between the male gender and the psychiatric symptom.

Dr. Marwaha comments on the findings, saying, "Cannabis use in young people is common and associated with psychiatric disorders. However, the prospective link between cannabis use and bipolar disorder symptoms has rarely been investigated."

According to the latest statistics from the National Institute on Drug Abuse, over 35 percent of 12th graders — who are usually 17–18 years old — said that they used marijuana in the year leading up to the survey, and 6 percent admitted to using it "daily or near-daily."