It's no secret that cannabis is considered one of the hottest investment trends of this generation on Wall Street. Although selling a processed plant isn't exactly what you might call innovative, the black market for global weed sales generates tens of billions of dollars each year. This means there are clear-cut reasons to believe that these illicit sales can be moved to legal channels in the years to come.

Since 1996, we've seen two-thirds of all U.S. states give medical marijuana the green light, with 11 of these states also allowing adult-use consumption and/or retail sales. Meanwhile, Canada became the first industrialized country in the modern era to legalize recreational cannabis in October 2018. North America "going green" has played a big role in more than tripling global marijuana revenue to $10.9 billion in 2018 from $3.4 billion in 2014.

But, according to The Global Cannabis Report from Prohibition Partners, this is really just the tip of the iceberg.

A handful of dried cannabis buds lying atop a messy pile of cash.

Image source: Getty Images.

Global marijuana sales could increase more than eightfold by 2024

The 87-page report, released this past week, suggests that worldwide legal weed revenue will increase to (drumroll) $103.9 billion by 2024. This would represent an 853% increase in sales from 2018, and equates to a compound annual growth rate of 45.6%, if accurate. For added context, the only other sales estimate that specifically focuses on 2024 comes from Arcview Market Research and BDS Analytics via the State of the Legal Cannabis Markets report. In this analysis, Arcview and BDS foresee $40.6 billion in global marijuana sales by 2024.

While there are dozens of Canadian growers vying for their share of the global cannabis market, a few, such as Canopy Growth, Aurora Cannabis (NASDAQ:ACB), Aphria, and Tilray, stand out for making the greatest strides to expand internationally. In particular, Aurora Cannabis and Canopy Growth are forecast to be Nos. 1 and 2 in terms of peak annual output, making them the likeliest candidates to focus on global marijuana growth in the not-so-distant future.

However, Prohibition Partners' robust growth estimate by 2024 isn't, arguably, the biggest surprise of its report. In fact, it's not even in the top five. Here are a few additional insights/estimates that might surprise you.

A person holding cannabis leaves in front of a globe of the Earth.

Image source: Getty Images.

1. Europe, not North America, will be the leading sales producer by 2024

Though all investors are currently focused on the North American market, The Global Cannabis Report portends that Europe will outpace North America in aggregate cannabis revenue by 2024. The expectation is that Europe will generate $39.1 billion in cannabis sales, with North America at $37.9 billion.

On one hand, Prohibition Partners sees the U.S. and Canada as being further along on the industry maturity and legalization front than Europe. On the other hand, Europe has a larger population, which is expected to play a bigger role in pushing legal weed sales beyond that of North America. After 2024, the report alludes that recreational legalizations could pick up in Europe, leading to an even larger sales outperformance, relative to North America.

A dried cannabis bud on top of a doctor's prescription pad.

Image source: Getty Images.

2. Medical marijuana sales will handily outpace recreational weed revenue

Not only is Europe forecast to outpace North America on cannabis spending, but Prohibition Partners expects medical marijuana revenue to easily outpace recreational sales by a margin of $62.6 billion to $41.3 billion.

Even though the recreational market is considerably larger than medical cannabis, the constraint here is that there won't be too many markets around the world that will have legalized adult-use marijuana five years from now. North America ($17.7 billion, est.) and Europe ($16.8 billion, est.) are expected to account for 84% of worldwide recreational sales by 2024, with Europe's adult-use pot sales likely picking up toward the latter half of the upcoming decade.

This is a great time to mention that top-tier grower Aurora Cannabis has at least 132,000 kilos of its annual output located in Europe (mostly in Denmark). The largest facility, Aurora Nordic 2, should be up and running next year.

Also, Flowr Corp. (OTC:FLWPF), while a small fry among growers, has a 7-million-square-foot outdoor grow farm located in Portugal. Flowr recently completed the acquisition of Holigen, giving it access to the Aljustel grow farm, which is capable of 500,000 kilos of annual output. While this production isn't going to meet the same ridiculously high-quality standards placed on Flowr's crop in Kelowna, British Columbia, it'll provide more than enough cannabis to produce high-margin derivatives for the European market.

A black silhouette of the United States, partially filled in by baggies of cannabis, rolled joints, and a scale.

Image source: Getty Images.

3. The U.S. will have legalized recreational pot by 2024

Another potentially shocking prognostication is that Prohibition Partners expects the U.S. to have legalized recreational pot by 2024. Despite 33 states having legalized medical marijuana in some form, cannabis remains a Schedule I (i.e., entirely illegal) drug at the federal level.

In order for this prediction to come to fruition, there would need to be significant turnover in Congress. Republicans have generally shied away from reforming cannabis in the U.S., and they currently have majority control of the Senate. What's more, Senate Majority Leader Mitch McConnell (R-Ky.) has purposefully blocked cannabis riders and legislation from coming to the floor for vote.

In short, it would take a real shake-up in Congress for the U.S. to legalize marijuana at the federal level.

A lab research technician holding up a beaker containing cannabinoid-rich liquid.

Image source: GW Pharmaceuticals.

4. There are 564 ongoing clinical trials involving cannabis

In spite of it not being a forecasted figure, it's incredible to note that, based on data supplied by the U.S. National Library of Medicine and Prohibition Partners, 564 clinical trials are currently ongoing that involve cannabis. Of these 564 studies, 343 are located in the U.S., 106 in Europe, 49 in Canada, and 35 in the Middle East.

These studies have the real potential to improve patients' lives. Remember, GW Pharmaceuticals (NASDAQ:GWPH) became the first company to have a cannabis-derived drug approved by the U.S. Food and Drug Administration in June 2018. GW Pharmaceuticals' lead drug, Epidiolex, reduced seizure frequency from baseline by 30% to 40% in late-stage trials for patients with two rare forms of childhood-onset epilepsy. Today, GW Pharmaceuticals is looking to expand Epidiolex's label, and is working on new cannabinoid-based therapies for indications such as spasticity associated with multiple sclerosis and autism spectrum disorder. 

A suspicious-looking man in a blue hoodie holding a potted cannabis plant.

Image source: Getty Images.

5. The black market will remain a big problem, even in a legalized environment

Finally, it's worth paying close attention to how Prohibition Partners derives its estimates, especially in relation to the black market. Here's the excerpt that really caught my eye:

Our recreational cannabis market sizes do not include the black market. If a country has yet to legalize recreational cannabis, the value of the market is 0. If legalized, appropriate growth curves are applied to the legal market thereafter, while capping the legal market at maximum 60% of the value of the entire recreational market (including the black market).

Note that part about "capping the legal market at a maximum of 60% of the value of the entire recreational market?" That's a fancy way of saying that at no point does Prohibition Partners believe a significant portion of the illicit market will be driven out. Or, put another way, 40% of all sales, at minimum, should remain in the black market.

The inability to drive out illicit producers is particularly noticeable in California, a state where consumers are being taxed as much as 45% on legal product. When compounded with the fact that close to 80% of the state's municipalities have banned recreational retail stores, it's practically rolled out the red carpet for the black market.

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.