(WTVO) — According to a new study, researchers have found that marijuana usage is causing a surge in schizophrenia cases in young men.

The National Institute of Drug Abuse estimated that 30% of schizophrenia cases in men of ages 21 – 30 are linked to cannabis use.

The study analyzed 6 million people and attributed 15% of schizophrenia diagnoses in men and women were due to marijuana.

The study factored in additional risk factors including alcohol use and parental history of schizophrenia.

“As access to potent cannabis products continues to expand, it is crucial that we also expand prevention, screening, and treatment for people who may experience mental illnesses associated with cannabis use,” said NIDA director Dr. Nora Volkow, who co-authored the study.

The study also noted that men are more likely to use the drug than women.

Past studies have uncovered links between marijuana and schizophrenia, although the cause is not entirely clear.

The drug is known to cause psychosis, impair thinking and decision-making, and make it difficult to handle emotions.

According to The Daily Mail, patients have suffered from symptoms including hallucinations and paranoia, and an inability to answer questions.

The condition is incurable and only treatable with anti-psychotic medications, experts said.

The NIDA has warned that too little is known about the health effects of marijuana to justify its widespread recreational use.

States like Illinois have legalized the recreational use of marijuana.

“There is, unfortunately, evidence to suggest that cannabis is increasingly seen as a somewhat harmless substance. This is unfortunate, since we see links with schizophrenia, poorer cognitive function, substance use disorders, etc,” Dr. Carsten Hjorthoj told CNN. “This study adds to our growing understanding that cannabis use is not harmless and that risks are not fixed at one point in time.”