Few, if any, industries are growing as quickly as legal marijuana. According to Marijuana Business Daily's 2017 report, "Marijuana Business Factbook 2017," legal U.S. weed sales are expected to grow by 30% in 2017, 45% in 2018, and an aggregate of 300% between 2016 and 2021 to approximately $17 billion. This rapid and consistent growth is exactly why investors have been drawn to marijuana stocks over the past couple of years.

The buzz surrounding marijuana hits an all-time high

But at the heart of this rapid rise in sales is a discernible shift in the way consumers view marijuana. Once seen as a dangerous drug, more and more Americans view marijuana to be less dangerous, in some instances, than alcohol. The belief is that as support for the legalization of cannabis gains steam, pressure on lawmakers in Washington to alter marijuana's scheduling will pick up. It's possible that if support for marijuana continues to increase, voters may choose to push incumbent representatives and senators out of office if their views don't represent that of their constituents.

A person with cupped hands holding cannabis leaves.

Image source: Getty Images.

The case for legalization got even stronger this past week when national pollster Gallup released its annual survey that questioned random adults around the country about their views on pot. Not surprisingly, the survey showed that support for legalizing marijuana hit an all-time record high for the second year in a row.

According to Gallup, 64% of Americans in the October poll now want to see weed legal nationally. That's up from 60% in 2016, 36% in 2006, and just 25% in 1995, the year before California became the first state to green-light medical cannabis for compassionate use.

Interestingly enough, this was also the first poll in Gallup's history where a majority of Republicans favored legalizing pot. Though the 51% in favor still falls within the margin of error that could drag this percentage below a "majority," it's a marked increase from the 42% and 37% support seen in years 2016 and 2015 from the GOP. This is noteworthy, considering that Republicans currently have majority control of the legislative branch of the government, and they had previously been one of two groups that wasn't in favor of pot's expansion, with senior citizens being the other. While this in no way suggests that Capitol Hill is suddenly going to do an about-face on its cannabis policy, the idea is no longer as far-fetched as it might have seemed even one or two years ago.

A row of voting booths for a U.S. election.

Image source: Getty Images.

Favorability could push more states to legalize

Even with a clear bifurcation between the federal government and states' rights with regard to cannabis, growing support for weed is likely to have new states legalizing the drug in 2018.

For example, Arizona voters went to the polls this past November and voted down Proposition 205, which would have legalized recreational pot, by just 2% (the "yes" votes tallied about 48%). This year and the next, pro-legalization groups have focused their efforts on Arizona, which lacked young adult turnout at the polls in 2016 (younger adults typically have a more favorable view of pot). History has shown that the second time is often the charm when it comes to legalizing weed, with California, Oregon, and Florida all failing to pass a marijuana measure this decade, then easily succeeding on their second go-around.

Hopes are high in the Motor City as well, with Michigan angling to get a recreational cannabis measure on its 2018 ballot. A lack of an organized legalization effort in 2016 doomed the movement, but pro-legalization groups have focused on Michigan for the 2018 election. Considering Michigan's budget is in desperate need of additional revenue to cover road and bridge repairs, as well as boost the state's education fund, Michigan looks to have a reasonable shot at passing a recreational-weed law in the upcoming year. 

A judge's gavel next to cannabis buds.

Image source: Getty Images.

But keep your expectations in check

Yet even though nearly two-thirds of Americans favor nationally legalizing pot, and a separate poll from Quinnipiac University in April 2017 shows that an overwhelming 94% favor legalizing medical cannabis, it'd be wrong to expect any major changes at the federal level, and in some cases at the state level, anytime soon.

For instance, both Vermont's House and Senate overwhelmingly voted in favor of legalizing adult-use weed earlier this year. However, Gov. Phil Scott (R-Vt.) wound up vetoing the bill, citing concerns that lawmakers in Congress often share. In particular, Scott cited worries about how the police would crack down on drivers who are under the influence of cannabis. Studies have shown that marijuana use leads to a clear adverse impact on driving ability, but there aren't any guidelines in place, as there are with alcohol, that lay out a line in the sand of what's acceptable and what isn't with regard to tetrahydrocannabinol (THC) in the bloodstream. THC is the psychoactive component of cannabis.

There are also concerns about what a home-grow option might entail. A full legalization usually allows folks to grow cannabis plants for medicinal or adult consumption purposes at their residence, which some opponents of pot's expansion opine could ease access of marijuana to adolescents. Some studies have suggested a link between heavy marijuana use as an adolescent and adverse impacts to long-term memory.

Attorney General Jeff Sessions giving a speech.

Attorney General Jeff Sessions. Image source: Jeff Sessions' Senate webpage.

But the biggest obstacle of all remains the federal government, or more precisely Attorney General Jeff Sessions, who hasn't hidden his disdain for marijuana's expansion one bit, and in May he even tried to coerce lawmakers in Congress to repeal the Rohrabacher-Farr Amendment, which currently protects medical marijuana businesses in the 29 states where medical weed is legal from federal prosecution. Sessions will stop at nothing to halt the expansion of cannabis, and he's champing at the bit for the opportunity to prosecute marijuana businesses.

As long as Sessions is attorney general, and the Trump administration remains in control of the legislative branch, the outlook for substantive change appears bleak for the marijuana industry, and investors.

The Motley Fool has a disclosure policy.