By Dennis Thompson
WEDNESDAY, April 26, 2017 (HealthDay News) -- An unintended byproduct of medical marijuana laws could be a sharper increase in illicit pot use, a new U.S. study reports.
Illicit pot use increased significantly more in states that passed medical marijuana laws compared to other states, researchers found in comparing three national surveys conducted between 1991 and 2013.
States with medical marijuana laws also saw an increase in people who can't stop using pot even though it's interfering with many aspects of their lives, researchers said. This is known as cannabis use disorder.
These laws "seem to send a message that use of this drug is safe and acceptable in some way," said lead researcher Deborah Hasin of Columbia University's Mailman School of Public Health.
The proliferation of medical marijuana dispensaries also might promote illicit use, said Rosalie Pacula, director of the RAND Corporation's Bing Center for Health Economics.
Medical marijuana states that restrict the number of dispensaries and tightly regulate the system appear to have different illicit pot use patterns from states like California and Colorado, where the laws amounted to a "de facto legalization system," said Pacula, who wasn't involved with the study.
"It's the commercialization of the medical marijuana industry that has led to spillover into this recreational market," she added.
California passed the first medical cannabis law in 1996. Today, a total of 29 states have approved medical marijuana, and eight states have legalized recreational pot use.
Hasin and her colleagues estimate that medical marijuana laws have led to an additional 1.1 million adults illicitly using pot and 500,000 more adults with a diagnosable cannabis disorder.
The researchers relied on data from more than 118,000 adults gathered in three national surveys stretching fom 1991 to 2013.
In 1991, no Americans lived in states with medical marijuana, but by 2012, more than one-third lived in states that had accepted medical pot.
The studies showed that illicit pot use in states that passed medical marijuana laws tended to lead non-legalization states by 1.4 percentage points on average. Medical pot states also led other states in cannabis use disorders by an average 0.7 percentage points.
The increase in cannabis use disorders could stem from the increasing potency of pot that has occurred under legalization, Hasin said.
These trends could become even more pronounced in states that have fully legalized recreational marijuana, she added.
"It seems like everything we might see with medical marijuana laws would be accentuated in recreational marijuana laws," Hasin said.
But these new findings run counter to other studies that have shown no increase in teen marijuana use after implementation of medical marijuana programs, said Paul Armentano. He is deputy director of NORML, a group advocating reform of marijuana laws.
"America's real-world experience with medical marijuana regulation . . . finds that cannabis can be legally produced and dispensed in a responsible manner that positively affects the lives of patients, but does not inadvertently or adversely impact overall public health or public safety," Armentano said.
Pacula added that people should be cautious in interpreting the new study, because it uses national survey data to evaluate state-level trends. Medical marijuana laws vary from state to state, so applying national data could miss serious geographic differences.
"When you are evaluating the effects of a state law on a sample that is not state-representative, it can be misleading," Pacula said.
For example, the study shows a decrease in marijuana use in California between 1991 and 2002, she noted.
"That right there should tell you something fishy is going on," Pacula said. "I'd like to see this study replicated with state-specific data."
The study was published April 26 in the journal JAMA Psychiatry.
Dr. Wilson Compton, deputy director of the U.S. National Institute on Drug Abuse, agreed that differences in state laws matter, including how many dispensaries are allowed under the law and how tightly they are regulated.
Compton compared these laws to laws that regulate alcohol in the states.
"The density of alcohol outlets is associated with how many problems we see from alcohol," said Compton, who cowrote an editorial accompanying the study.