The marijuana industry is growing like a weed, and investors have certainly taken notice. Far more marijuana stocks than not have seen their valuations double, or perhaps run even higher, over the trailing 12-month period.

Why are marijuana stocks in such high demand? Look no further than public opinion toward marijuana and the growth of legal weed sales.

According to a 2016 Gallup poll and an April 2017 CBS News poll, the percentage of respondents who would like to see recreational cannabis legalized nationally has jumped to a respective 60% and 61%, both all-time highs. By comparison, Gallup's 1995 poll showed just 25% approval for such a move, while the CBS News poll was a full 21-percentage-points lower just six years ago. The public wants change at the federal level, and investors are trying to beat that change by purchasing marijuana stocks.

A cannabis bud sitting atop a pile of cash.

Image source: Getty Images.

Legal pot sales have also soared. Investment firm Cowen & Co. is looking for $50 billion in legal annual cannabis sales by 2026, while a more recent report from Marijuana Business Daily implies that legal U.S. sales could triple between 2017 and 2021, to more than $17 billion. You'd probably struggle to find such consistent growth in any other industry or sector.

Which marijuana stock could hit $1 billion in sales first?

However, there are dozens of marijuana stocks to choose from, and they're clearly not all going to be winners. The top performers, assuming marijuana remains legal in select states and that it gains broader approval in Canada and Mexico, are probably going to be the pot-based businesses that can really ramp up revenue and turn a healthy profit.

If there is a "Holy Grail" milestone out there for pot stocks, it's the $1 billion sales mark. The first cannabis company to hit $1 billion in sales will likely validate the industry -- at least in some psychological way -- to Wall Street and investors. But which marijuana stock has the best chance at being first to $1 billion in annual sales? My guess is it'll come down to these five:

1. GW Pharmaceuticals

Arguably the most logical choice is cannabinoid-based drug developer GW Pharmaceuticals (GWPH), which also happens to be the largest pot stock by a mile in terms of market cap.

What makes GW Pharmaceuticals so special is its currently experimental cannabidiol therapy Epidiolex, which hit its primary endpoint in pivotal phase 3 trials for two rare types of childhood-onset epilepsy. In both its Dravet syndrome and Lennox-Gastaut syndrome trials, Epidiolex led to a statistically significant reduction in seizure frequency compared to the placebo.

The success of these studies puts the company on track to get Epidiolex approved by the Food and Drug Administration (FDA), though nothing is ever a guarantee when it comes to the FDA. Assuming some potential for label expansion, Epidiolex could very well hit $1 billion in peak annual sales, if not a tad higher. 

Cannabis leaves next to lab test tubes and equipment.

Image source: GW Pharmaceuticals.

2. Corbus Pharmaceuticals

Corbus Pharmaceuticals (CRBP -6.90%) is considerably more of a wildcard than GW Pharmaceuticals, but if one specific clinical trial goes its way, it could easily leap to $1 billion in annual sales.

Corbus' pipeline consists of a solitary drug known as anabasum, which is a synthetic oral endocannabinoid-mimetic drug that binds to the CB2 receptors expressed on immune cells and fibroblasts. Its drug is being tested in four indications, but one stands out head and shoulders above the rest: cystic fibrosis (CF). There are few drugs to treat CF, and most that are FDA approved target a very specific mutation, making their impact limited within the CF community. Anabasum is believed to have a global anti-inflammatory effect, meaning it could be taken by most, or all, CF patients.

The downside? Even though anabasum hit its primary endpoint of a 75% reduction in the pulmonary exacerbation event rate in phase 2 trials, it didn't provide any improvement in lung function as measured by the forced expiratory volume within the first second (FEV1) test. FEV1 improvement is often seen with FDA approved CF drugs, leaving anabasum's impact on CF somewhat uncertain.

3. Canopy Growth Corp.

Another seemingly logical marijuana stock that could thrive is Canopy Growth Corp. (CGC -0.20%), a producer and retailer of medical cannabis products and oils in Canada. Medical weed has been legal in Canada since 2001.

Canopy Growth has been a busy bee of late on the acquisition front. It completed its acquisition of Mettrum Health earlier this year, and it acquired a 472,000 square foot facility that includes its current corporate headquarters.

Growth by acquisition gives the company immediate access to more medical marijuana patients and the ability to rapidly expand its growing capacity. This could come in handy considering that Canada is currently reviewing legislation that would make recreational pot legal in the country by next summer. If that were to happen, Canopy Growth would presumably see a major surge in demand.

An indoor commercial cannabis grow farm.

Image source: Getty Images.

4. Aphria

One of Canopy Growth's largest competitors in the Canadian medical marijuana producing and retail business is Aphria (NASDAQOTH: APHQF). Aphria has the distinction of being the most prominently profitable marijuana stock, with the company reporting five consecutive quarterly profits.

Unlike Canopy Growth, Aphria is doing things organically. It's been funding expansions of its existing grow capacity, and is currently working on its most aggressive growth initiative to date, Phase IV.

The Phase IV expansion will allow for 75,000 kilograms of increased cannabis capacity, and it'll push the company's grow capacity from a mere 300,000 square feet to 1 million square feet. It won't come cheap, though, as the project required a capital investment of roughly $100 million. You can bet that Aphria's management is crossing its fingers that Canada legalizes recreational weed.

5. Aurora Cannabis

And how can we forget Aurora Cannabis (ACB -3.65%), yet another of Canada's medical cannabis producers and retailers. Aurora Cannabis has lagged its peers in recent profits due to its expansion-based spending.

Like Aphria, Aurora Cannabis is all about organic development (with the exception of a recent 40,000 square foot facility purchase). Aurora Cannabis has touted its Aurora Sky project, which will increase its grow capacity nearly ninefold, as the most technologically advanced and automated cannabis-grow facility in the world, when completed. All told, it's expected to add 800,000 square feet of grow capacity, and it could begin production at just the right time with Canada currently reviewing the aforementioned recreational pot legislation.

A jar of cannabis buds atop a stack of money.

Image source: Getty Images.

And the winner is...

Now that you're aware of the likely contenders, which marijuana stock is liable to hit $1 billion in sales first?

If my arm were twisted, I'm going to stick with GW Pharmaceuticals, given the success of Epidiolex in late-stage studies. Just the two rare indications alone, assuming approval and a successful launch, could easily get the company more than halfway to $1 billion in sales within three years after launch.

Corbus would be my second choice, but it has a major obstacle to overcome, considering the lack of promising FEV1 data. This isn't to say anabasum's other indications aren't important, so much as to indicate that they probably won't lend to $1 billion in combined annual sales without the company succeeding with its CF trial. If the company's phase 3 trial demonstrates FEV1 improvement, my thinking here could change dramatically.

Why no love for the Canadian growers, you ask? While it's tough to say what the dynamics of supply and demand would do to marijuana prices in Canada if its government chooses to legalize pot, it's a pretty safe bet that we would probably need to see a tripling or quadrupling in grow capacity (at minimum, and depending on the company in question) before they'd even have an outside shot at $1 billion in annual sales. Canopy Growth, Aphria, and Aurora still have a ways to go with developing their current projects or acquisitions, which makes them less likely to hit $1 billion in sales anytime soon.