Cannabis may be just a plant, but it's fully captivated an investing audience over the past couple of years. In North America, sales of legal cannabis catapulted higher by 33% in 2017 to $9.7 billion, according to cannabis research firm ArcView. Within a few years' time, they could be nearing $25 billion. A decade from now, ArcView suggests that $47 billion annually in legal weed sales is fully possible. This is the type of sales growth that Wall Street and investors simply can't ignore.

Since 1996, we've witnessed almost three-fifths of all U.S. states approve the use of cannabis in some form, with nine having legalized recreational cannabis. We've also witnessed a sustainable shift in the way the public views pot. Gone are the days where cannabis was considered taboo. Nowadays, politicians are expected to discuss their stance on marijuana when campaigning, and parents can freely talk about cannabis with their children. An October 2017 poll from Gallup found 64% support for legalizing marijuana nationally. 

Cannabis buds next to a piece of paper that says yes, and lying atop miniature Canadian flags.

Image source: Getty Images.

This simply hasn't happened before in the marijuana industry

Each and every year, the cannabis industry brings with it surprises and "marijuana firsts." For example, earlier this year we witnessed Cronos Group, a Canadian-based investment firm with full or partial ownership in three growers, become the first marijuana stock to uplist from the over-the-counter exchange to the Nasdaq. Chances are, 2018 isn't done with these so-called marijuana firsts. Here are three more that I believe you should expect before the year is over.

1. A developed country legalizes the sale of recreational marijuana

Tops on the list is the expected legalization of recreational weed in Canada by this summer. Though Canada won't be the first country in the world to have legalized recreational pot -- that title goes to Uruguay -- it will be the first developed country to have done so.

Legalizing marijuana for adult sale in Canada has been a longtime coming. Prime Minister Justin Trudeau has campaigned to do so for years, but it finally looks as if it'll come to fruition. A Senate vote is scheduled for June 7, with legalization occurring shortly thereafter, assuming passage in the Senate. Following a presumed legalization, adult sales would commence in either August or September, with the lag time of eight to 12 weeks between approval and consumer sales representing the time needed to get the product in retail outlets from growers.

The chances of the Senate voting in favor of legalization appears extraordinarily high. Conservatives who oppose such a move are handily outnumbered by progressives in Canada's parliament. Furthermore, an excise tax proposal has been laid out, with all but one province (Manitoba) agreeing to a two-year tax-sharing agreement with the federal government. The ducks are certainly in a row for legalization, which should open the door to $5 billion or more in added annual sales. 

Cannabis leaves next to biotech lab equipment.

Image source: GW Pharmaceuticals.

2. The U.S. Food and Drug Administration approves a cannabinoid-based drug

Next, this very much looks like the year we'll see the FDA give the thumbs-up to a cannabinoid-based drug.

The regulatory agency for experimental pharmaceutical products is currently reviewing GW Pharmaceuticals' (NASDAQ:GWPH) lead drug, Epidiolex, which is designed to treat two rare forms of childhood-onset epilepsy -- Dravet syndrome and Lennox Gastaut syndrome. Epidiolex is a cannabidiol (CBD)-based medicine, and CBD is the nonpsychoactive component of the cannabis plant. A PDUFA review data is currently set for June 27, albeit it's possible the FDA delivers a verdict before then. 

What makes Epidiolex such an exciting compound is what it was able to do in both indications. In two pivotal-stage trials for each indication (so, four total late-stage trials), Epidiolex met its primary endpoint of a statistically significant reduction in seizure frequency relative to baseline. In particular, it tripled the performance of the placebo in terms of seizure frequency reduction from baseline (39% versus 13%) in one Dravet syndrome study. 

However, investors should understand that an FDA approval for Epidiolex has seemingly been baked into GW Pharmaceuticals' share price for quite some time. Coming to market with a possible list price of $30,000 to $60,000 annually, GW Pharmaceuticals' marketing team has quite the task ahead in terms of gaining insurer, physician, and even patient support. 

A smiling senior man in a hat holding out a medicinal cannabis joint.

Image source: Getty Images.

3. Seniors change their tune on pot

Finally, and perhaps the biggest stretch of the three, I believe we'll see seniors change their stance on cannabis for the first time ever when Gallup comes out with its annual poll in October 2018.

In recent years, two groups had taken an unfavorable stance toward pot: seniors and Republicans. In 2017, this changed. According to Gallup, 51% of respondents who identified as Republican were in favor of legalizing cannabis. Even though this is still within the survey's margin for error, it's the first time Republicans have favored the idea of nationally legalizing cannabis. That left seniors as the only group still opposed to legalization. 

However, seniors' dislike toward the green rush has abated in recent years. In October 2016, Gallup found that 45% of seniors (defined as age 55 and over) favored legalization, up from just 29% between 2003 and 2005. As time has passed, baby boomers who have a more favorable view of cannabis have pushed into the "senior" category, by Gallup's definition, ultimately improving favorability. Given that most seniors support medical marijuana, I'd go out on a limb and suggest that 2018 could be the first year we see a majority of seniors support broad-based legalization. 

Of course, keep in mind that polling will have virtually no impact on Congress' view of cannabis, nor will it affect marijuana stock valuations. But as favorability toward pot grows, it may become tougher for politicians in Washington to sweep the issue under the rug.

Now, we wait to see if these predictions prove prescient or preposterous.

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.