What we know for sure is that the United States is in the midst of an opioid epidemic that is killing tens of thousands of Americans each year. In 2016, 42,000 Americans died from heroin or opiate overdose, according to the Centers for Disease Control and Prevention.

It is understandable that people want desperately to find a way to prevent and stop the staggering loss — but it is also important that we prevent the spread of misleading information that can cause and compound harm. So, after a review of recent medical literature, I have to just get straight to the bottom line: It is premature and dangerous to lead anyone to believe that marijuana legalization lowers a state’s prevalence of opioid overdose.

For example, even though Colorado has allowed marijuana use for medical reasons since 2001, the state reported a record number of opioid deaths in 2017.

Marijuana industry-funded billboards across metro Denver deceptively claim states with “legal” marijuana have fewer opioid deaths. Similarly, news reports reaching millions of people in minutes flat present only pieces and parts of research studies to support this claim. What practically no one is explaining is that none of these studies — not one — ever will be able to show that marijuana legalization causes opioid overdose death rates to fluctuate up or down.

Why? Because there are simply too many possible confounds for which these studies cannot control. These include:

• variable access to buprenorphine, methadone and other substance treatments. Access varies greatly from state and state and from community to community.
• availability of the opiate overdose antidote, naloxone. States where there is more opiate use may have more access to emergency treatments for overdose.
• heroin potency, which may vary from state to state.
• incarceration rates, prison-diversion programs and a wide array of other state demographics.

Associations between marijuana use and opiate use

Before taking a look at what recent research has to say about associations between marijuana laws and opiate deaths, let’s look at the associations research has found between marijuana use and opiate use. Consider:

• Adults who use marijuana compared to those who do not are about six times more likely to use opioids without a prescription and for non-medical reasons. Adult marijuana users are also eight times more likely to have an opioid use disorder at a three-year follow-up. (Source: Olfson et al., 2018., Am J Psychiatry 175:47-53)
• People with chronic pain who use marijuana do not use lower doses of opioid painkillers compared to people with chronic pain who do not use marijuana. (Source: Degenhardt et al., Drug Alcohol Depend 147:144-150) The fact that marijuana has only modest effects on pain may explain this finding. (Source: Nugent et al., 2017. Ann Intern Med 167:319-331)
• The world’s largest longitudinal study on cannabis use and pain found no evidence that cannabis reduces pain or opioid use. The study was published in The Lancet, one of the world’s most respected publishers of medical research.
• Youth who use marijuana are 2-3 times more likely to progress to other substance use, compared to youth who do not use marijuana (Source: Smith et al. 20313, Drug Alcohol Dependence 132:63-68) And the age at which a youth uses marijuana is a significant predictor for risk of subsequent injection drug use The odds of ever injecting drugs are decreased by 27 percent for every delayed year of marijuana initiation. (Thurstone et al. American Journal of Addiction. 2013 Nov-Dec. 22(6); 558-565)

Associations between marijuana legalization and opiate deaths

The findings of studies looking at links between marijuana laws and opiate deaths are conflicted — which is all the more reason to remain skeptical about claims that marijuana legalization cuts opiate death rates. Consider:

A 2018 study published in the Journal of the American Medical Association reports that states with medical marijuana laws compared to those without have 5.88 percent fewer opioid prescriptions per 1,000 Medicaid enrollees. States with recreational marijuana compared to those without medical or recreational marijuana have 6.38 percent fewer opioid prescriptions per Medicaid enrollee. (Source: Wen H, Hockenberry JM. JAMA Internal Medicine. epub ahead of print. 2018).

OK, so those are Medicaid enrollees. Not all opiate abusers are on Medicaid. This simply isn’t enough information to support claims that marijuana legalization is the reason for fewer opiate-related deaths. It is also very important to note that this is a cross-sectional study — meaning a study that looks at one snapshot in time, not over a period of time with continual follow-up. This study also is not controlled for any of the variables cited above.

In a similar study, states with medical marijuana compared to those without were found to have fewer doses of opioids dispensed among Medicare Part D enrollees. The authors report this finding was more robust in states with medical marijuana dispensaries. (Source: Bradford et al. JAMA Internal Medicine. epub ahead of print. 2018)

This study has the same limitations as the one cited immediately above. What about everyone else who is abusing opiates and not receiving Medicare Part D? It is also a significant overstatement of this study’s findings to claim legal marijuana is a reason for fewer opiate-related deaths.

In a Colorado study, commercialization of recreational marijuana in 2014 corresponded to a small decrease in the number of opioid overdoses in the state. (Source: Livingston et al., American Journal of Public Health 107:1827-1829) Similarly, a Journal of Health Economics study reports lower rates of opioid overdose in states with medical marijuana and especially in states with commercialized dispensaries. (Source: Powell et al., 2018. Journal of Health Economics 58:29-42). Yet another study found that compared to states without medical marijuana, states that do have it report a 24.8 percent lower rate of opioid overdose. (Source: Bachuber et al., JAMA Internal Medicine 174:1668-1673)

Again, we are not looking at randomized, controlled trials. The same confounds listed above — including heroin potency, access to treatment and overdose prevention measures — are not accounted for. And it must be reiterated that Colorado reported a record number of opioid deaths in 2017 — so citing a 2014 correlation is not nearly enough to claim credibly that marijuana legalization laws lessen opiate death rates.