The leaf of a marijuana plant under a grow light at Oaksterdam University, July 22, 2009, in Oakland, California. (Photo by Justin Sullivan/Getty Images)

While a growing number of states have legalized marijuana for medicinal purposes in recent years, new research may contradict the positive aspects of the drug being touted by its advocates. Marijuana has helped with pain but also heightened the risk of schizophrenia in patients, according to a new report published by the National Academies of Sciences, Engineering and Medicine on Thursday.

“There is substantial evidence of a statistical association between cannabis use and the development of schizophrenia or other psychoses, with the highest risk among the most frequent users,” the study’s conclusions for mental health reported.

The study also listed conclusions for any evidence linked to therapeutic effects, cancer, cardio-metabolic risks, respiratory disease, immunity, injury/death, natal exposure, psychosocial, problem cannibal use, abuse of other substances and challenges for conducting cannabis research.

Some of the benefits of cannabis use included: significant evidence for relieving chronic pain in adults, antiemetics in chemotherapy and improving patient-reported multiple sclerosis symptoms. Marijuana could also help with “improving short-term sleep outcomes in individuals with sleep disturbance associated with obstructive sleep apnea syndrome, fibromyalgia, chronic pain and multiple sclerosis,” the report said.

Cannabis has been legalized in more than half of the states in the country, some for medicinal use and others for recreational. Alabama Sen. Jeff Sessions – the attorney general nominee for President-elect Donald Trump’s proposed administration and opponent to marijuana legalization – said during his confirmation hearing that he would enforce federal law regardless of states' laws regarding cannabis.

"It's not so much the attorney general's job to decide what laws to enforce. We should do our job and enforce laws as effectively as we're able,” Sessions said Tuesday.

He was previously quoted in a Senate drug hearing this past April stating he thinks “Good people don’t smoke marijuana.”

“We need grown-ups in charge in Washington to say marijuana is not the kind of thing that ought to be legalized, it ought not to be minimized, that it’s in fact a very real danger,” Sessions said at the time.