LAS VEGAS — Research suggests that as the use of opioids decreases, in part because of the difficulty obtaining these drugs, use of cannabis increases, especially as more states allow medical or recreational use.
However, this so-called substitution hypothesis doesn't hold true, at least from an individual drug user perspective, researchers say.
Rather, a new study shows that the number of users who combine marijuana with opioids has increased in recent years, as has the amount of these drugs they consume.
"We found support for the synergistic effect on an individual level; people who tend to use more marijuana also tend to use more opioids," said Scott Novak, PhD, senior research scientist at RTI International, a leading research institute in Research Triangle Park, North Carolina.
This, said Dr Novak, could signal a dangerous trend. The findings were presented here at PAINWeek 2015.
Although the substitution hypothesis has gained traction recently, "we were hearing quite the opposite" from those abusing these drugs as well as from "local informants," said Dr Novak.
The studies that did show a trend toward substitution were small and included participants who inject drugs. "We wanted to look at this taking a large-spectrum, community-wide approach," said Dr Novak.
The researchers used data from the 2003 and 2013 National Survey on Drug Use and Health (NSDUH), an annual computer-aided, interviewer-assisted survey of noninstitutionalized US civilians aged 12 and older. The sample size was about 55,000 for each year.
For the surveys, participants were asked about past-year use of nonmedical pain relief. Such use was defined as "without a doctor's prescription" or "for the experience or subjective feelings it causes."
The study found that past-year cannabis use increased 16% (10.8% to 12.6%) over the 10-year period. Nonmedical prescription pain reliever use decreased by 14% (4.9% to 2.2%). "So at the population level, it looks like there was the substitution effect," said Dr Novak.
However, in both 2003 and 2013, higher levels of cannabis use were associated with more frequent consumption of prescription pain relievers.
"We found that among dual users, those who were using more marijuana also used more opioids," said Dr Novak. "The finding was replicated in 2003 and in 2013, so 10 years apart we found a synergistic effect."
Dr Novak noted that during the 10 years, an increasing number of states passed medical marijuana legislation. The year 2013 was just before retail or recreational marijuana "came into play," he said.
But he doesn't think that laws surrounding marijuana use played much into the numbers uncovered by his study. "We think it's an artefact; that people are liking the effect of opioids and cannabis together."
What's worrisome is that the positive association between cannabis and opioid use is growing stronger. The study found that over time, people were using these drugs more often; there were more opioids days and more cannabis days.
"If this trend continues, in the next 3 or 4 years, we could see a very alarming rate because essentially, it's going to come to point where people are using both these drugs almost on a daily basis," said Dr Novak.
The researchers looked at sex, age, and education and didn't find any patterns with regard to dual users. They also didn't find significant differences by region.
Looking more closely at whether marijuana users start consuming opioids or opioid users start taking marijuana is the next step, said Dr Novak.
It's also unclear whether users combine the drugs for increased pain relief or for pleasure. In interviews with dual users for other projects, these participants indicated that "pain relief and euphoria are kind of wrapped up together," said Dr Novak.
Combining these drugs could lead to adverse health effects, he said. "We're starting to learn a lot more about opioids and metabolism and pharmacokinetics, about the effects of using opioids with alcohol and not with alcohol, and about the effects on a full stomach and not on a full stomach, but nobody has looked at opioids with marijuana and no marijuana. You can only assume that it probably has a bad effect," both in the short and long term, he speculated.
For example, research shows that combining these drugs can impair cognitive performance and organ function and increase risk for respiratory depression. "You have two drugs that fundamentally operate to depress the respiratory system," noted Dr Novak.
He suggested that clinicians who prescribe opioids might want to ask their patients whether they're also using marijuana. Doctors used to take a "don't ask, don't tell" approach to drug use, but with increasing combination of agents screening becomes all the more important.
The study showed alcohol use remained stable at 65.5% during the 10-year period.
Another study carried out by RTI researchers and presented at the PAINWeek meeting, which also used NSDUH data from 2002 to 2012, showed that the culture around marijuana permissiveness might influence legalization.
The study found that states that passed marijuana legislation had higher marijuana use rates 5 years before and in the last data year available before legalization compared with states that did not legalize marijuana.
The authors noted that of the 23 states with medical marijuana laws, 5 have passed legislation that allows for the possession and recreational use of marijuana among those aged 21 years and older.
Commenting on this research for Medscape Medical News, Armando Villarreal, MD, assistant professor, neurosurgery, Rochester Neurosurgical Partners, New York, said that while the data seem to suggest that culture around permissiveness might affect legislation, other factors play a role a role in establishing that culture.
"Among them are the unemployment rate, the median level of education, religion, and political ideals," he said.
Less than half of all states have passed medical marijuana laws, and only 10% of the states now allow recreational use. "So the idea that we are about to see a sudden influx of states that will legalize marijuana seems to me overreaching."
Dr Villarreal, who gave a separate presentation on "the science behind marijuana as an analgesic" at the meeting, said physicians should become familiar with local laws surrounding use of marijuana because their patients will ask their opinion. But he stressed that prescribing marijuana should be influenced only by available scientific data and not by public opinion.
"Currently the data is scant, mainly due to federal government laws that make it extremely difficult to do good research. I believe there is an urgent need to change these laws so that better information regarding the therapeutic use of marijuana becomes available."
The studies using the NSDUH data were supported by RTI International. Dr Villarreal receives research support from Medtronic and is Associate Supporter of the Canadian Consortium for the Investigation of Cannabinoids.
PAINWeek 2015. Posters 87 and 24. Presented September 9, 2015.
Medscape Medical News © 2015 WebMD, LLC
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Cite this: Number Using Opioids and Marijuana on the Rise - Medscape - Sep 15, 2015.