March 18 (UPI) -- Many people given a medical marijuana card to ease pain, anxiety or depression symptoms become addicted to the drug, a study published Friday by JAMA Network Open found.
In addition, those in the study who use marijuana to treat those symptoms did not see any improvement, though some with insomnia experienced improved sleep, the data showed.
People using medical marijuana at greatest risk for developing the symptoms of cannabis use disorder, or addiction, were those seeking relief from anxiety and depression, the researchers said.
This suggests the need for stronger safeguards over the dispensing and use of these cards as well as close monitoring of patients given them, they said.
"There have been many claims about the benefits of medical marijuana for treating pain, insomnia, anxiety and depression, without sound scientific evidence to support them," co-author Jodi Gilman said in a press release.
"We learned there can be negative consequences to using cannabis for medical purposes," said Gilman, an associate professor of psychiatry at Harvard Medical School.
"Medical" marijuana has been cleared for use in 36 states and the District of Columbia, according to the National Conference of State Legislatures.
In addition, there are efforts to standardize the medical use of the drug at a national level.
Although users tout the benefits of the drug, there is limited scientific evidence supporting its therapeutic value for a number of conditions.
There is also some research suggesting that the composition of the medical marijuana products available varies, which may impact effectiveness.
People issued medical marijuana cards, which prove they are allowed to use the drug legally, suffer from a variety of conditions, from anxiety and depression to chronic pain and sleep disorders, Harvard Health says.
The cards require written approval from a licensed physician who, under the current system, is typically not the patient's primary care provider, but rather a so-called "cannabis doctor," Gilman and her colleagues said.
These cannabis doctors may provide authorization to patients with only a cursory examination, give no recommendations for alternative treatments and provide no follow-up, the researchers said.
The medical marijuana industry functions outside regulatory standards that apply to most fields of medicine, including Food and Drug Administration oversight, they said.
The symptoms of cannabis use disorder, or marijuana addiction, include the need for more cannabis to overcome drug tolerance and continued use of it despite physical or psychological problems caused by the cannabis, according to the National Institute on Drug Abuse.
For this study, Gilman and her colleagues tracked 186 adults, with an average age of 37 years, from the Boston area who were interested in obtaining a medical marijuana card for 12 weeks.
Of the 186 participants, 105 were given medical marijuana cards immediately, while the rest were placed on a waiting list for 12 weeks, the researchers said.
Those issued the cards were nearly twice as likely to develop cannabis use disorder compared to those on the waiting list, the data showed.
In addition, by week 12, 10% of the patients with medical marijuana cards had been diagnosed with cannabis use disorder, including 20% of those who obtained a card to help treat anxiety or depression, the researchers said.
Regardless of the specific health condition for which the drug is prescribed, regulation and distribution of cannabis to people with medical marijuana cards must be improved greatly, they said.
"Our study underscores the need for better decision-making about whether to begin to use cannabis for specific medical complaints, particularly mood and anxiety disorders, which are associated with an increased risk of cannabis use disorder," Gilman said.
"There needs to be better guidance to patients around a system that currently allows them to choose their own products, decide their own dosing and often receive no professional follow-up care," she said.