Source: Flickr user Isabel Mancera.

Regardless of which president takes office in two more years, one thing is becoming clear: Marijuana is increasingly becoming a part of American consumers' agenda.

Marijuana takes center stage
Over the past decade, the public's opinion surrounding whether or not marijuana should be legalized has done a complete 180. Just one in four respondents in a Gallup poll would have been in favor of marijuana's legalization just a decade ago. As of 2013, this figure had jumped to 58%, signaling that many view the drug more favorably for a number of reasons.

For starters, there's the belief that marijuana possesses medical properties that could be beneficial in treating certain diseases. This is the primary reason we've witnessed 23 states legalize marijuana for medical purposes since 1996. Florida tried to become the 24th state in this past election, but it fell 2% shy of the 60% needed to officially pass the amendment and change Florida's constitution.

Source: Flickr user

However, the enthusiasm goes beyond just marijuana's medical benefits. The movement to pursue adult-use legalization of the drug is gaining steam in a number of states. In 2012, Washington and Colorado legalized recreational use marijuana. Oregon and Alaska doubled the number of recreation-legal states in 2014 when their residents approved a similar law.

Both medical marijuana and recreational marijuana help individual states generate tax revenue that they can use to close budget gaps, so select states where marijuana isn't currently legal are seriously considering putting the measure to vote.

Yet, putting aside public opinion, a number of concerns remain in the forefront. Perhaps none is greater than the long-term effects marijuana smoking might have on the health of a person. Look around, and you'll certainly get a wide range of opinions -- and with good reason. You see, a vast majority of studies involving marijuana's effects on the body over the past few decades have targeted its potential risks rather than its benefits. There simply aren't many long-term studies to establish a safe track record for marijuana.

However, one long-term study that recently emerged from Emory University could have Americans changing their view on marijuana.

I bet you didn't see this coming
According to an abstract published online ahead of a print publication in the Annals of American Thoracic Society, smoking one marijuana cigarette per day for as long as 20 years wasn't associated with any adverse effects on lung function.

Source: Flickr user Ashton.

Specifically, researchers noted that marijuana smoke exposure in adults aged 18 to 59 wasn't associated with a decline in FEV1 values, or the maximum amount of air you can exhale within one second. A decline in FEV1 would be expected with chronic or obstructive lung diseases, such as asthma or COPD, which can be caused by lifelong smoking of tobacco products.

It should be noted that the method of marijuana inhalation mattered as well. Those who smoked combustible marijuana cigarettes were more likely to report increased symptoms of bronchitis. For those individuals who vaporized their marijuana, there were considerably fewer reports of adverse respiratory symptoms. In spite of a higher propensity to get bronchitis, the conclusion that marijuana smoke leads to no long-lasting adverse effects on the lungs would appear to be a major victory for marijuana proponents.

Why this study is important
This study and the need for others like it are important for marijuana supporters as it potentially distances marijuana from the known harmful effects of smoking tobacco products, and it offers the idea that marijuana could be used over the long term in moderation without causing any major damage to a user's lungs.

In the 23 states where marijuana is legally allowed to be prescribed for medical purposes, cancer is a common qualifying condition. However, there are a number of other potentially long-term conditions like glaucoma, chronic pain, and hepatitis C, for example, where medical marijuana may be prescribed over the long term. Thus it's important to understand how long-term use of medical marijuana might affect the user. Based on this latest study, the results demonstrate that medical marijuana's benefits could outweigh its risks.

Source: GW Pharmaceuticals.

It's also a positive for high-profile cannabinoid drug developer GW Pharmaceuticals (NASDAQ:GWPH), which is looking to use its more than five dozen cannabinoid compounds to effect positive biological change. In its pipeline, GW Pharma's most promising candidate is Epidiolex for adult and childhood epilepsy, but it has other experimental therapies as well to treat type 2 diabetes and cancer pain. The more beneficial long-term studies GW Pharma can get behind (even though its products aren't smoked or vaporized) the more publicly acceptable it could be for GW to target unmet childhood indications with cannabinoid-based products.

Still a long way from approval
But even with this markedly positive study on moderate long-term use, marijuana is still, admittedly, a long way away from being approved across the board.

It's highly unlikely that the federal government is going to change its tune on marijuana as a schedule 1 drug anytime soon. In fact, marijuana supporters should be counting their blessings that the federal government has allowed the individual states to manage their own marijuana laws by taking a hands-off approach. However, if the laws within those states break down or fail to keep legally grown marijuana within a states' borders, it could invite the federal government to take a more active role in policing the drug.

We also have to bide our time until more studies analyzing the long-term effects of marijuana are available. Until researchers have a better understanding of how marijuana affects cognitive function over the long run, it could place a cap on marijuana's expansion into new states or even across the country.

As an investor, I continue to believe this is one to avoid. Traders are emotional, and there aren't solid business models in place behind a majority of marijuana companies. Even GW Pharmaceuticals is likely to lose money throughout the remainder of the decade. From a consumer standpoint, it's really anyone's guess. Marijuana does have the potential to generate substantial tax revenue, but until some of these aforementioned questions have answers, it's unlikely to gain serious traction.