In case you haven't noticed, marijuana stocks have garnered a lot of buzz on Wall Street in 2019 (and over the last three-plus years, for that matter). The Horizons Marijuana Life Sciences ETF, the first cannabis exchange-traded fund, has more than tripled the return of the broad-based S&P 500 on a year-to-date basis. That's because investors are all in on the prospect of global marijuana sales growing by fourfold to sixfold over the next decade.

But it hasn't all been roses for pot stock investors. While most of the industry has performed well, including a small handful of companies that have risen by between 2,000% and 7,000% just since the beginning of 2016, three marijuana stocks recently hit all-time lows.

A visibly worried man looking at a plunging stock chart on his computer monitor.

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MedMen Enterprises

Though most vertically integrated dispensary operators in the United States have seen their valuations soar after announcing an acquisition (or multiple buyouts), upscale dispensary operator MedMen Enterprises (MMNFF) has moved to an all-time low. If MedMen's shares sink even another 5%, it'll no longer boast a billion-dollar market cap.

Superficially, there are a number of things to like about MedMen. Namely, its oldest locations in Southern California have been selling slightly more on a square-foot basis than Apple stores. This demonstrates that not only does the upscale cannabis store model work, but that the company has been successful in normalizing the cannabis-buying process, at least for the consumers it's been attracting.

MedMen also has one of the largest troves of retail licenses, with the company closing in on having license to open up nearly seven dozen locations, inclusive of its pending acquisition of PharmaCann for $682 million. Florida is an especially lucrative opportunity for MedMen, with the company angling for 30 stores in the Sunshine State, where marijuana is currently only legal from a medical perspective.

The company is also well-capitalized, thanks to $250 million in aggregative financing via Gotham Green Partners. Thus, running out of capital isn't exactly a concern.  

A large dispensary sign, with a cannabis leaf and the word dispensary written underneath it.

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So what gives then? The issue is that unlike a number of other multistate operators, MedMen is losing money hand over fist, and its sequential growth at existing stores has slowed substantially. Preliminary third-quarter sales look to have grown by 22%, but this factors in acquisitions in Nevada and Arizona. Remove these inorganic growth channels and focus solely on its Southern California stores, and sales grew by just 5% from the sequential second quarter.

Furthermore, MedMen's operating expenses totaled $73 million in the fiscal first quarter, $78 million in the fiscal second quarter, and they may have risen again in Q3, given that it has more operating stores than ever before. This suggests that profitability may not be in the cards until 2021 or later.

Ultimately, it's an intriguing concept with strong sales in a handful of stores, but MedMen's sustainability over the long run is still in question, as evidenced by its plunging stock and steep operating losses.

Insys Therapeutics

Another pot stock that recently fell to a record low is drug developer Insys Therapeutics (INSY). Poor Insys has been clobbered so hard that if you've got a buck in your pocket, you could buy a share of Insys...and still have money left over. But I wouldn't exactly suggest doing that, for a variety of reasons.

Insys and close to half a dozen of its executives, including billionaire founder John Kapoor, were implicated in a racketeering scheme that involved bribing physicians to prescribe fentanyl-based sublingual spray Subsys for off-label use, all while tricking insurers into covering the medication. Subsys is approved to treat breakthrough cancer pain, but documents showed that it was being prescribed by certain physicians to treat chronic pain of any variety. A recent guilty verdict has put the nail in the proverbial coffin for Subsys, with net sales plummeting to just $78.8 million in 2018, down from $330 million in 2015.

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Making matters worse, Insys' FDA-approved oral dronabinol solution known as Syndros -- dronabinol is a synthetic form of tetrahydrocannabinol, the cannabinoid that gets a user high -- has completely face-planted as a treatment for chemotherapy-induced nausea and vomiting, and as a treatment for anorexia associated with AIDS. Once pegged for maybe $200 million to $300 million in peak annual sales, Syndros delivered a meager $3.3 million in sales in 2018, its first full year on pharmacy shelves, and less than $4.8 million since its launch in the summer of 2017.

Insys is also dealing with big-time cash problems. On top of a $127.7 million operating loss in 2018, Insys' auditors included a going-concern warning in its most recent annual filing with the Securities and Exchange Commission. A going-concern warning is issued if insufficient capital is available to meet total liabilities over the next 12 months. Or, put another way, the company's declining sales of Subsys, virtually nonexistent sales of Syndros, and massive settlement with U.S. regulators may cause it to go belly up.

As I suggested earlier, you'd be wise to keep that buck in your pocket.

TILT Holdings

Another cannabis train wreck is TILT Holdings (TLLT.F -6.54%), which was formed out of a complicated four-way reverse takeover and began trading publicly on Dec. 6, 2018. Following a brief rally in January, shares of TILT have fallen to an all-time low.

The idea behind of combining four separate businesses sounded great on paper, but things haven't exactly been on point from an accounting standpoint. The four businesses included a Massachusetts dispensary operator, a Canadian pot grower, a cannabis-delivery software developer, and a customer-relationship software creator. TILT looked to offer solid channels of revenue growth once combined.

An accountant checking figures line by line with the aid of a calculator.

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The issue TILT ran into was a $496.4 million writedown in the fourth quarter that led to the company reporting a $552 million loss in 2018. This writedown was due to revaluing TILT Holdings' businesses.

As a refresher, the company filed prospectus documents on Dec. 5 (the day before it began trading as a combined company via the reverse takeover) showing $921 million in pro forma asset value. It then announced on May 1 that, as of Dec. 31, 2018, accounting changes caused it to remove almost a half billion dollars in asset value. In less than four weeks, TILT's perceived value declined by $496.4 million. That's a good way to send a publicly traded stock to new lows.

Then again, this writedown wasn't a big surprise. After all, 80% of TILT's $921 million in total assets was recognized as goodwill on the Dec. 5 prospectus, signaling that this business was built on promises and premiums rather than tangible assets. Now, with all faith lost in management, TILT is going to need a major turn of events to reverse its decline.