Growth in the marijuana industry over the past year has been absolutely phenomenal, and investors who have looked past the risks associated with investing in marijuana stocks have greatly benefited.

Three reasons pot stocks are soaring

As a whole, most marijuana stocks have doubled or tripled over the trailing-12-month period. This optimism is a direct result of rapidly changing consumer opinions of the drug, ongoing North American legalization efforts, and explosive legal sales figures.

According to a 2016 Gallup poll and a recently released CBS News poll, support for a nationwide recreational marijuana legalization is now at an all-time high of 60% for Gallup and 61% for CBS News. Support for legalizing medical cannabis nationally is even higher, with CBS News reporting 88% support and an independent Quinnipiac University poll finding 93% support.

Cannabis buds falling out of a jar onto a pile of cash.

Image source: Getty Images.

State-level expansion has also been a boon for marijuana stocks. Five U.S. states legalized medical marijuana last year, bringing the total number of legal medical weed states to 28. Additionally, Mexico has moved to legalize medical cannabis.

In terms of recreational pot, the number of legal U.S. states doubled to eight in 2016 with residents in Maine, Nevada, Massachusetts, and California voting in favor of their states' respective cannabis measure in November. Canada is also currently working through legislation introduced by Prime Minister Justin Trudeau that would legalize recreational weed throughout the country by as early as next year.

And finally, legal marijuana sales in North America are soaring. Cannabis research firm ArcView estimated legal North American sales growth at 34% in 2016 to $6.9 billion, and it sees growth continuing on an annual basis at north of 25%. As an investor, you'd struggle to find quicker and more consistent growth prospects.

The only three marijuana stocks that delivered a quarterly profit

However, not all marijuana stocks are created equal.

The vast majority of pot stocks lost money in their most recent quarterly report, including Insys Therapeutics, which had been profitable for years. Insys' lead drug, Subsys, a sublingual breakthrough cancer pain med that has nothing to do with marijuana, is facing a number of lawsuits and reduced sales, pushing Insys to a quarterly loss.

But three marijuana stocks delivered a profit in their latest quarterly results. Let's briefly take a look at these pot stocks and see if they're worth a deeper dive.

An indoor commercial cannabis grow farm.

Image source: Getty Images.

1. Aphria Inc.

One of the more impressive streaks of profitability comes from Canadian medical marijuana cannabis producer and retailer Aphria (NASDAQOTH: APHQF), which in mid-April reported its fifth consecutive quarterly profit.

For the quarter, Aphria reported 91% year-over-year sales growth to $3.75 million, largely a result of increasing demand in Canada for medical cannabis products, as well as Aphria's expanding grow capacity. Aphria is in the midst of a multiphase organic expansion that saw it spend approximately $100 million on its phase 4 project. This expansion will eventually boost its growing capacity to 1 million square feet from 300,000 square feet, and it'll add 75,000 kilograms of annual cannabis production.

Despite higher capital costs associated with this project, Aphria maintained a 70% gross margin in its fiscal third quarter, and generated more than $736,000 in earnings before interest, taxes, depreciation, and amortization (EBITDA). That was well over double what it generated in the year-prior period. The end result was a quarterly net income of $3.63 million after adjustments.

Aphria may only be touching the tip of the iceberg, too. With Canada's government tinkering with the idea of legalizing recreational weed, it could easily switch its priorities to supplying the adult-use market, if approved. With its phase 4 project expected to be completed early in 2018, Aphria is a marijuana stock to get on your watchlist.

Grow lights hovering over an indoor cannabis grow farm

Image source: Getty Images.

2. Canopy Growth Corp.

It may not come as a huge shock that another one of the three profitable marijuana stocks is a Canadian medical cannabis producer and retailer, Canopy Growth Corp. (NASDAQ:CGC). Canopy Growth is the second-largest pot stock by market cap at $1.1 billion, and it's a direct competitor of Aphria.

Two factors have been instrumental in allowing Canopy Growth to produce a quarterly profit: its competitive size advantage and its branding strategy.

Both Aphria and Aurora Cannabis are in the process of organically expanding their grow capacity in Canada. However, Canopy Growth has been an aggressive acquirer of other companies, which has boosted its current production capacity well ahead of its two peers. With its acquisition of Mettrum Health now in the books as of the end of January, it has six licensed facilities and about 665,000 square feet in grow capacity. The ability to meet higher demand now could give Canopy Growth some clear industry advantages.

Canopy Growth has arguably also differentiated its medical cannabis products better than any other grower. Its Tweed brand is well-known in a number of Canada's markets, and it packs some celebrity firepower given its branding partnership with rapping mogul Snoop Dogg for three cannabis strains.

The result? The company now has access to about half of Canada's medical marijuana patients, who generated $7.14 million in third-quarter sales, representing 180% year-over-year sales growth, and it produced a $2.2 million quarterly profit, reversing a year-ago loss of $2.4 million. Like Aphria, demand could be on the verge of heating up, so Canopy Growth could be worth a closer look.

A cannabis plant under special LED lightning.

Image source: Getty Images.

3. Scotts Miracle-Gro Company

The final profitable "marijuana stock" might be a bit of a head-scratcher for some: Scotts Miracle-Gro (NYSE:SMG), though still a traditional lawn care and garden business, has planted quite the seed in the hydroponics market -- and it's beginning to pay off.

Since Scott's is all about optimizing the ability of plants to grow, it's been working its way into both the lighting aspects and soil and nutrient demands of the weed industry. Its subsidiary, Hawthorne Gardening Co., is behind these pot-focused upgrades. Hawthorne has been on a pretty big acquisition spree in recent months, which is a primary factor that's boosted growth in its hydroponics segment.

According to the company's recently reported second-quarter results, U.S. consumer sales dipped 7% to $962.5 million. However, on a comparative basis and excluding acquisitions that pushed sales of its "other" category growth up 50% from second-quarter 2016, Scott's hydroponics portfolio delivered 22% year-over-year growth.

Said CFO Thomas Randy Coleman in a September quarterly conference call, "In states where laws have evolved to allow the legal cultivation of cannabis, in almost every one of those states, that's happening using hydroponic growing methods. We have the benefit of growing from that."

For the entire second quarter, Scott's generated a hearty $2.73 in adjusted per-share profit. As legalization efforts expand, Scott's could see quite a boon from legal pot sales. Though it doesn't break out the profitability of its hydroponics business, a few more quarters of 22% year-over-year growth could coerce that disclosure from eager marijuana stock investors.

Needless to say, Scott's Miracle-Gro is also worth keeping on your radar.

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.