Many investors are understandably excited about the opening of Canada's recreational marijuana market. It's certainly a big deal. The Canadian market could easily top $5 billion in annual sales.

But some CEOs of marijuana companies, including Canopy Growth (NYSE:CGC) co-CEO Bruce Linton and Tilray (NASDAQ:TLRY) CEO Brendan Kennedy, have thrown around huge figures for the global marijuana market. These numbers make Canada's market look like a mere drop in the bucket.

Just how big will the worldwide marijuana market really be? It depends on your perspective.

Shadow of a dollar sign on a pile of marijuana leaves

Image source: Getty Images.

$150 billion?

Tilray CEO Brendan Kennedy has publicly stated that cannabis is a $150 billion industry. Where does Kennedy's number come from? The company's investor presentations cite the source as the United Nations World Drug Report, which includes projections for the illicit marijuana market.

Using $150 billion as the global marijuana market size makes sense -- if you think marijuana will be fully legalized throughout the world in the near future. For now, though, only Canada and Uruguay allow the legal use of marijuana for recreational purposes.

Several countries have legalized medical marijuana, and more are likely to do so over the next few years. And while marijuana remains illegal at the federal level in the U.S., 30 states and counting have legalized medical marijuana. But the reality is that the market size for the medical use of marijuana doesn't come close to the $150 billion level that Tilray references.

$500 billion?

If the $150 billion market size seems too high, hold on to your britches. Last week, Canopy's Bruce Linton told Jim Cramer, host of CNBC's Mad Money, that cannabis could disrupt a $500 billion global market. How did Linton arrive at such an eyepopping number?

Linton started with the illegal marijuana market, which he said currently totals around $200 billion -- a higher number than the U.N. figure cited by Tilray. He then listed several other industries that cannabis could potentially disrupt -- alcohol, cigarettes, and pharmaceuticals. Linton said that a $500 billion estimate is more accurate than lower "conservative, cautious" predictions.

The global alcoholic beverages market size is estimated to be between $1.3 trillion and $1.5 trillion. There appears to be a good chance that cannabis-infused beverages could capture part of this market. Major alcoholic beverage maker Constellation Brands was bullish enough about the potential for cannabis that it recently invested $4 billion in Canopy Growth.

Linton thinks that cannabis products could disrupt the cigarette market by being used for smoking cessation. The worldwide tobacco cigarette market (outside of China) is estimated to be at least $680 billion. The smoking-cessation product market is much smaller, of course. But it's growing -- and could reach close to $22 billion by 2024.

The global pharmaceutical market totals more than $1.1 trillion. However, cannabis and cannabinoid drugs only target indications representing a fraction of this market. Currently, the only approved cannabinoids in the U.S. are for treating rare forms of epilepsy, nausea and vomiting caused by chemotherapy, and loss of appetite in AIDS patients who have lost weight. Still, the potential exists for cannabinoids to help address other indications, including arthritis and insomnia.

More tangible numbers

Here's the reality: The legal global marijuana market isn't anywhere close to $150 billion or $500 billion right now. Arcview Market Research and BDS Analytics methodically researched all the available data to determine an estimate for the global marijuana market size. They peg the 2017 total at roughly $9.5 billion.

But Canadian recreational marijuana sales will help push the global market size higher. So will growth in international medical marijuana markets such as Germany and the United Kingdom. The more important growth driver, though, will be the U.S.

Arcview and BDS Analytics project that the global marijuana market will reach $32 billion by 2022. Nearly three-quarters of that -- $23.4 billion -- will come from the U.S. Can the marijuana market increase significantly more than that over the long run? Absolutely.

It's possible that more countries will legalize recreational marijuana. More U.S. states could do so as well. Federal marijuana laws in the U.S. could change in a way that really opens the market up. But for the next few years, a market size closer to $32 billion seems much more realistic than the $150 billion and $500 billion figures being thrown around.

Smartest moves for investors

Investors are better off focusing on more realistic near-term projections than far-off potential market estimates. Remember, CEOs have a reason for talking up the potential market size: It makes their companies' market caps seem less astronomically high.

With the U.S. generating the lion's share of total worldwide marijuana sales, it's also a good idea to expand your investing horizon to include stocks that can profit from the U.S. market. So far, Canopy and Tilray haven't done much in the U.S. due to federal marijuana laws. However, keep your eyes open for any moves by these or other companies to expand into the U.S. in ways that are legal at the federal level or could soon be, including buying cannabinoid-focused biotechs or establishing hemp operations.

There's an old saying that if wishes were fishes, we'd all swim in riches. For now, any talk about $150 billion and $500 billion marijuana markets only reflects wishes.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool recommends Constellation Brands. The Motley Fool has a disclosure policy.