The marijuana industry is, for lack of a better pun, sprouting like a weed. According to cannabis research firm ArcView, the North American legal weed market grew by 34% in 2016 and is expected to expand by a compound annual rate of 26% through 2021. By 2021, we could be talking about a market worth $21.6 billion, which has certainly caught the attention of investors.

Fueling this growth has been a major shift in the way the public views cannabis. Gallup, which has conducted marijuana perception polls for the past 47 years, found in Oct. 2016 that 60% of the U.S. population favors legalizing pot nationally. That's up significantly from the 25% who favored such a measure in 1995, the year before California became the first state to legalize medical cannabis. 

A person holding a cannabis leaf in the middle of a grow farm.

Image source: Getty Images.

However, this doesn't mean cannabis has a cakewalk toward legalization. Despite 29 states giving the green light to medical weed, and residents in eight states voting to legalize recreational pot, the federal government has dug in its heels on its current schedule I categorization. A schedule I drug is wholly illegal and has no recognized medical benefits.

Attorney General Jeff Sessions has been particularly instrumental in blocking progress at the federal level. Sessions is, perhaps, the most ardent opponent on Capitol Hill, and as recently as May, he requested the repeal of the Rohrabacher-Farr Amendment, which protects legally operating medical-marijuana businesses from federal prosecution.

Recreational marijuana just reversed this deadly trend in Colorado

At the heart of the marijuana debate is one question: Can weed actually provide health benefits that outweigh its risks? According to a recently published study in the American Journal of Public Health, the case that it can has been made sufficiently stronger. 

The recently published study from researchers at the University of North Texas and University of Florida examined the impact of recreational cannabis' legalization in Colorado, which began selling the drug for adult use in Jan. 2014, as compared to opioid-related deaths. Opioids are a class of prescription medicines typically administered to treat various types of chronic and severe pain. They can also be a highly addictive medication that, in 2015, led to 20,101 related prescription deaths, according to the American Society of Addiction Medicine. 

A man standing at a fork in the road. One path leads to prescription pills, and the other to cannabis leaves.

Image source: Getty Images.

Researchers noted a clear and defined increase in opioid-related deaths in Colorado in the 14 years prior to the legalization of recreational cannabis. However, what was truly noteworthy was the recognized decline in opioid-related deaths of 6.5% since adult-use marijuana was introduced, somewhat reversing the so-called opioid epidemic within the state. 

This study also appears to corroborate findings from a trio of authors who, in Oct. 2014, published a report in JAMA Internal Medicine that noted similar benefits for patients. This study found a roughly 25% lower mean annual opioid overdose-mortality rate in states that had legalized medical cannabis compared to those that hadn't between 1999 and 2010. 

It should be plainly noted that researchers can't concretely conclude that marijuana's legalization is directly the cause of this decline in opioid-related deaths. Nonetheless, researchers did a pretty good job of adjusting their results of external factors, suggesting that these results may be the real deal. In other words, patients prescribed opioids indeed may be substituting for cannabis instead -- and since there have been no recorded instances of cannabis-related overdose deaths in 2015 or 2016, it's a perceived "safer" alternative. This would jibe well with a study published earlier this year that showed 92% of Americans prefer medical cannabis to opioids, if given the choice. 

This isn't the first time cannabis has demonstrated the power to heal

What's often overlooked is that this study isn't the first time we've seen cannabis demonstrate its power to improve the health or well-being of people. GW Pharmaceuticals (NASDAQ:GWPH), a premier developer of cannabinoid-based drugs, dazzled in multiple phase 3 trials with its oral cannabidiol-based treatment for two rare types of childhood-onset epilepsy. In particular, GW Pharmaceuticals' drug, Epidiolex, wound up reducing seizure frequency for Dravet syndrome patients by 39%. 

Cannabis leaves next to biotech lab equipment.

Image source: GW Pharmaceuticals.

Insys Therapeutics (NASDAQ:INSY), a drug developer with a primary focus on treating pain through the use of cannabinoid-based drugs and synthetic opioids, was given the green light from the Food and Drug Administration (FDA) last year for Syndros, an oral dronabinol solution that's essentially a synthetic form of tetrahydrocannabinol (THC), the psychoactive component of cannabis. Syndros proved effective in treating chemotherapy-induced nausea and vomiting, as well as anorexia associated with AIDS. Insys launched this first-of-its-kind drug two months ago. 

A little over three weeks ago, clinical-stage drug developer Zynerba Pharmaceuticals (NASDAQ:ZYNE) reported encouraging data from its midstage study involving ZYN002, a cannabidiol-based gel, in children with Fragile X syndrome. The study met its primary endpoint by achieving a 46% improvement in the total score of Anxiety, Depression, and Mood Scale at week 12 compared to baseline. 

The list could go on, but it's also not perfect. Clinical trials involving cannabis have also failed, including a Zynerba study involving ZYN002 for epilepsy patients with focal seizures, as well as GW Pharmaceuticals' Sativex (which is approved throughout Europe), which failed a phase 3 cancer pain study in the United States.

Don't expect change anytime soon

Even with this clinical data in the bag and a number of studies suggesting that cannabis can bring health benefits and/or quality-of-life improvements to the table, the chance of the federal government changing its tune under Donald Trump's watch are probably slim to none.

Jeff Sessions speaking to a room full of people.

Image source: Jeff Sessions' Senate webpage.

As noted, Jeff Sessions will seemingly stop at nothing to thwart the progress of medical and recreational cannabis. Sessions had this to say to a room of Attorney Generals earlier this year:

Marijuana is a cure for opiate abuse? Give me a break! This is the kind of argument that's been made out there to just -- almost a desperate attempt to defend the harmlessness of marijuana or even its benefits. I doubt that's true. Maybe science will prove I'm wrong. But at this point in time, you and I have a responsibility to use our best judgment, that which we've learned over a period of years, and speak truth as best we can. My best view is that we don't need to be legalizing marijuana.

The marijuana industry is also caught up in what you might consider a Catch-22. Lawmakers in Congress want additional clinical studies run to better understand the benefit-versus-risk profile of cannabis. However, running these studies is almost impossible given the tight regulations involved with getting approval to conduct clinical studies for a schedule I substance.

Long story short, cannabis may be a pathway to fighting opioid addiction, but I wouldn't count on the red carpet being rolled out for the medical weed industry anytime soon.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.