"A billion here, a billion there, pretty soon you're talking about real money."

This quote is frequently attributed to the late Sen. Everett Dirksen, but he apparently never said those exact words. Of course, $1 billion is real money regardless of what anyone says or doesn't say.

Quite a few states are on track for real money to be made in the cannabis industry over the next few years. Seven states are projected to claim marijuana markets with spending of $1 billion or more by 2022, according to a report published recently by ArcView Market Research and BDS Analytics. Which states made the list -- and are there opportunities for investors? Here's what you need to know.

1. California

California doesn't have to wait to have a billion-dollar marijuana market. Last year, cannabis spending in the state approached $3 billion. By 2022, this total is projected to jump to $7.7 billion -- boosted significantly by California's recreational marijuana market that opened for business earlier this year. The California marijuana industry's total output, which measures the total economic impact rather than direct spending only, could be nearly $15 billion in the next four years.

2. Colorado

There's also another state that is already seeing real money spent on marijuana: Colorado. Marijuana spending in the state totaled $1.5 billion last year, including both medical and recreational sales. This figure is expected to increase to around $2.5 billion in 2022. The total output of the cannabis industry in Colorado at that time is projected to be roughly $4.6 billion. This growth rate isn't as impressive as California's primarily because the marijuana market in Colorado is more mature.

3. Florida

Florida's marijuana spending last year didn't come close to the $1 billion mark, with an estimated $192 million spent on medical cannabis in The Sunshine State. By 2022, though, this spending is projected to soar to more than $1.7 billion with a total output of nearly $3.3 billion.

4. Washington

Like California and Colorado, Washington allows the legal use of both medical and recreational marijuana. Total marijuana spending in the state was $934 million -- not quite at the $1 billion level. However, four years from now, Washington could see marijuana spending of close to $1.5 billion with a total output of around $2.8 billion.

5. Michigan

Michigan currently claims one of the largest medical cannabis markets in the United States. In 2017, medical marijuana spending totaled $812 million. Michigan residents will vote in November on whether to legalize adult use of recreational marijuana. This measure is likely to win approval. If so, marijuana spending in the state could increase to $1.4 billion by 2022, with a total output of $2.6 billion.

6. Massachusetts

Massachusetts' medical cannabis market size was around $151 million last year. However, the state's recreational marijuana market opened in July 2018. Growth in this market is expected to drive marijuana spending in Massachusetts to more than $1.2 billion by 2022, with a total output of close to $2.3 billion.

7. Arizona

Arizona already has a thriving medical marijuana market. In 2017, marijuana spending totaled $461 million. Within the next four years, the figure could jump to around $1.2 billion with total output of $2.2 billion. It should be noted that ArcView Market Research and BDS Analytics do expect that Arizona will legalize recreational marijuana, but the companies' market projections assume that legalization won't take effect until 2021.

Investing alternatives

How can investors profit from the tremendous growth that's projected for the U.S. marijuana market, especially in these seven states? One alternative is to look north to Canada.

At least three Canadian marijuana stocks have strong ties to the cannabis industry in California -- CannaRoyalty, Sunniva, and MedMen Enterprises (OTCBB:MMNFF). Actually, MedMen is a U.S.-based company that operates cannabis dispensaries but listed its stock on the Toronto Stock Exchange.

There are also other U.S. stocks that trade on over-the-counter (OTC) markets with solid cannabis credentials. MariMed (OTC:MRMD) and iAnthus Capital Holdings (OTC:ITHUF) ranked as the top two best-performing marijuana stocks of all in the first half of 2018. MariMed is a professional management company that serves the cannabis market and also sells cannabis edibles. iAnthus owns marijuana growing facilities in four states, including two on our list -- Florida and Massachusetts.

Another U.S. OTC marijuana stock that has attracted a lot of attention from investors is Kush Bottles (OTC:KSHB), which sells packaging and supplies to marijuana dispensaries and growers. Thanks to a recent acquisition, the company also now hydrocarbon gases used to convert cannabis plants into oils.

In my view, though, one of the best options for investors looking to capitalize on growth in the U.S. marijuana market is Scotts Miracle-Gro (NYSE:SMG). It's the leading supplier of hydroponics products to marijuana growers. Unlike the other stocks mentioned, Scotts is listed on a major U.S. stock exchange and is therefore subject to stringent reporting requirements.

The company should profit as the U.S. marijuana market expands, but Scotts also makes most of its revenue from selling consumer lawn and garden products. Perhaps the best thing about Scotts Miracle-Gro is that it already makes "real money": Scotts is on track to record revenue of more than $2.5 billion this year.

Editor's note: A previous version of this article incorrectly stated that the 2017 medical cannabis market in Massachusetts was $151 billion rather than the correct figure of $151 million. The Fool regrets the error.