The US Centers for Disease Control (CDC) estimates that nearly 50 million people (about 18% of Americans) have used cannabis at least once making, it the most frequently used federally illegal drug in the country. Thirty-eight states, three territories, and the District of Colombia (DC) allow medical use of marijuana. Earlier this month, Ohio became the most recent state to legalize non-medical (often called recreational) use of cannabis. Currently, twenty-four states, two territories, and DC allow recreational use of marijuana.
Expansion of state governments legalizing or decriminalizing cannabis has led to a rapid increase in recreational use. Because of the regulations applied to the medical use of cannabis, the recent increases in recreational use have raised some concerns regarding the potential gains in cannabis use disorder (abbreviated CUD or CanUD).
The Diagnostic And Statistical Manual Of Mental Disorders (Fifth Edition) defines CUD as “a problematic pattern of cannabis use leading to clinically significant impairment or distress.” CUD occurs in about one-third of cannabis users. At the same time, research has linked chronic cannabis use to many health complications, including a higher prevalence of lung cancers associated with inhalation and an elevated schizophrenia risk.
In addition to adverse health effects, some reports suggest that increases in cannabis use result in decreased motivation attributed to biological reductions in the production of dopamine, a neurotransmitter that regulates many bodily functions.
With the rapid increase in cannabis use and the expected continued uptake of use as legalization expands, a firm understanding of risks related to CUD becomes necessary. A team of researchers at Yale sought to add to the knowledge base on CUD and performed a genetic analysis, which they published last week in Nature Genetics.
The researchers performed a genome-wide association study (GWAS), a scientific strategy to identify genetic variations associated with risk for a disease. The data came from the Million Veteran Program (MVP), a program run by the Veterans Affairs (VA) focused on genetic and lifestyle factors (including military experiences and exposures) that affect health outcomes. Over 1 million Veterans have joined the MVP program, generating a diverse cohort for genetic research.
The study included a meta-analysis with data from 1,054,365 individuals representing four ancestries. The cohort included 886,025 individuals with European ancestry, 123,208 individuals with African ancestry, 38,289 individuals with Admixed American ancestry, and 6,843 individuals with East Asian ancestry.
The findings identified genetic variants found in genes that encode receptors on nerve cells. These genetic variants conferred an elevated risk of developing CUD. Importantly, the researchers found that the variants associated with CUD also increased lung cancer risk.
The authors noted that the study could not distinguish between the full impact of cannabis and the effect of inhaling combustion products, including tobacco smoke. Despite this and other limitations of the study noted by the authors, the findings suggest a need to anticipate future health consequences related to increased cannabis use.
Sources: NBC News, JAMA Network, DSM-5 (page 509), JAMA Psychiatry, Eur Respir J, Schizophr Bull, Biological Psychiatry, Nature Genetics, Scientific Reports
