Few industries, if any, have been able to compete with the rapid growth rate of legal marijuana in recent years. According to cannabis research firm ArcView, the North American legal weed industry is expected to grow at a compound annual rate of 26% through 2021, to about $21.6 billion. Chances are that you won't find a higher, more consistent growth rate, which is why marijuana stocks have been blisteringly hot recently.

The public's softening views toward cannabis is a critical reason why weed has returned so much green to investors of late. An April 2017 CBS News poll found that an all-time record 61% of respondents want to see marijuana legalized across the country, and around 9 in 10 are in favor of legalizing the substance for medical purposes. 

A cannabis plant growing in an outdoor commercial farm.

Image source: Getty Images.

Cannabis' expansion could be halted by the federal government at any time

However, the pot industry's expansion could very easily be stopped in its tracks should the U.S. federal government decide to enforce its superseding laws on marijuana. At the federal level, marijuana is a schedule I substance, which means it's entirely illegal and has no recognized medical benefits. Should the Trump administration choose, it could scale back leniencies that have existed since Barack Obama was president and enforce stricter regulations on the recreational and/or medical-cannabis industry. And as a reminder, now-former White House press secretary Sean Spicer intimated in February that the Trump administration would get tougher on marijuana, but didn't offer any details. 

This battle between proponents and opponents of weed has escalated in recent years. Unfortunately for the proponents of pot, there's not a lot that can be done on Capitol Hill. Aside from the fact that Congress is currently too focused on healthcare and tax reform to even remotely consider rescheduling cannabis, a Catch-22 exists that makes it incredibly difficult for lawmakers to get the data they consider vital to reconsidering marijuana's scheduling.

In other words, lawmakers want a lot more clinical evidence on marijuana's benefits and risks, but running these studies has proven exceptionally difficult because of its schedule I status. Without this evidence, Congress is unlikely to budge on its current scheduling of marijuana.

Worse yet for proponents, the evidence from more informal studies doesn't always work in their favor.

This new data suggests marijuana could kill

Nearly two weeks ago, a team of five authors published a study in the European Journal of Preventative Cardiology that examined the impact of marijuana use on a person's cardiovascular system. The results of the study raised some eyebrows, to say the least.

A lab researcher with a white coat making notes in the middle of a hemp grow farm.

Image source: Getty Images.

The 1,213 subjects in the study were lumped into two groups in 2005: those who had used marijuana at some point ("marijuana users") and those who had never used marijuana ("nonusers"). After this grouping was complete, the researchers then pulled death statistics data from the U.S. National Center for Health Statistics in 2011. After adjusting for factors like gender, race, educational status, and tobacco use, to name a few factors, researchers concluded that there was a hazard ratio for death from hypertension of 3.42 for marijuana users compared to nonusers. In plainer English, marijuana users were deemed to be 3.42 times more likely to die of high blood pressure (hypertension) than nonusers.

Furthermore, the study appeared to show that the risk factor increased by 1.04 with each year of marijuana use. This led the study's authors to conclude that "marijuana use may increase the risk of hypertension mortality."

Of course, the findings of researchers aren't exactly concrete. To begin with, the study failed to take into account the level of marijuana use among confirmed users. A recent Gallup poll found that a record 45% of Americans have tried marijuana, but just 12% admitted to being regular smokers. Using marijuana once, or a few times, won't accurately reflect what impact cannabis is having on a person's heart.

Additionally, researchers didn't take into account the various types of cannabis strains that could impact the heart. Per Business Insider, marijuana may contain up to 400 compounds, and the mix and match of these compounds can differ wildly between regulated and unregulated markets. In short, no direct causation can be made from this study -- although the correlation does merit further research.

A book on federal and state marijuana laws next to a judge's gavel.

Image source: Getty Images.

It'll be a slow path to progress

Though informal, studies like the one above suggest that progress on the cannabis front is going to be slow at the federal level. As long as Jeff Sessions is the attorney general, there seems to be little shot of having marijuana rescheduling or de-scheduled. It also doesn't appear that marijuana is a priority for President Trump, with healthcare and tax reform on the table.

What does this mean for the pot industry and marijuana stocks? The answer is probably more of the same: uncertainty and losses.

Businesses that are primarily involved in cannabis often have two major hurdles they need to contend with, and those won't be expected to abate anytime soon. These challenges include having little-to-no access to basic banking services, such as a checking account, and having to pay higher taxes than so-called "normal" businesses since the Internal Revenue Service doesn't allow businesses that sell federally illegal substances to take normal corporate income tax deductions. This makes it that much harder for marijuana stocks to grow and turn a healthy profit for shareholders.

While it's anyone's guess what the future holds for the cannabis industry, this writer would strongly suggest that investors keep their distance.

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