Over the past couple of years, the marijuana industry has been breaking down barriers with regular frequency. In 2018, we saw Canada become the first industrialized country in the modern era to legalize recreational cannabis, and watched as GW Pharmaceuticals had its cannabis-derived drug Epidiolex approved by the U.S. Food and Drug Administration. Then, in 2019, we saw marijuana reform bills actually reach the House floor for vote, marking the first time in history that's happened.

As we ready to turn the page on 2019 and the decade, investors are primed to witness marijuana history take place once again in 2020. Here are three "marijuana firsts" you can be on the lookout for next year.

A large cannabis dispensary sign in front of a retail store.

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1. Adult-use sales begin for the first state to legalize cannabis without a ballot initiative

Investors won't have to wait long to see history made in 2020. On Jan. 1, Illinois dispensaries will open their doors and allow for the sale of recreational marijuana. The Land of Lincoln is one of 11 states that have given the green light to adult-use consumption, with most of these states also allowing for the sale of recreational weed.

What makes the legalization of recreational cannabis in Illinois unique is twofold. First, it's the only state-level weed legalization to include an expungement clause for people previously convicted of a cannabis offense. Attempts were made in New York and New Jersey to pass something similar in 2019, but their respective proposals failed to garner enough support to head to vote.

Second, and most important, this was the first time a state's legislature had voted to legalize recreational marijuana and allow for its sale. The emphasis on the last part has to do with Vermont's having legalized consumption via a legislative vote, but not the sale of adult-use pot. Illinois may have just set the blueprint for other states to follow.

From an investment perspective, Illinois is limiting the number of dispensaries that can be opened by a licensed operator to 10. Thus, you can count on multistate operators like Cresco Labs (OTC:CRLBF) and Green Thumb Industries (OTC:GTBIF) to have as many stores open as possible when the green flag waves. Green Thumb currently has five retail locations and three cultivation centers in the Land of Lincoln, with Cresco Labs operating five retail locations as well, with more on the way. The State of the Legal Cannabis Markets report from Arcview Market Research and BDS Analytics projects Illinois for $1.14 billion in annual sales by 2024, making it a core market for Cresco and Green Thumb.

A judge's gavel next to a small handful of dried cannabis buds.

Image source: Getty Images.

2. The first Supreme Court-mandated legalization takes shape

Next, investors will get to see another country (other than Canada and Uruguay) legalize recreational pot. By no later than April 30, our southerly neighbor, Mexico, will become only the third country worldwide to allow for the sale and consumption of adult-use marijuana.

What makes this upcoming legalization so interesting is that it's been entirely mandated by Mexico's Supreme Court. You see, in late October 2018, Mexico's highest court issued a ruling that an absolute ban on the recreational consumption and possession of weed was unconstitutional. This happened to be the fifth such occasion that Mexico's Supreme Court reached the same verdict, which in our southerly neighbor sets the standard throughout the country. In effect, Mexico's high court mandated that marijuana be legalized and set a one-year timeline for lawmakers in Congress to amend existing regulations to establish a retail market.

However, Mexico's congress wound up missing this deadline and more or less begged the Supreme Court for an extension to the deadline, which was granted. Lawmakers now have until the end of April to agree upon regulations that would allow for a legal retail market to be established in Mexico.

While it's unclear what the final bill will entail, an initial look at a proposal that was close to passage in late October shows that Mexico wants to keep big businesses from having licensing priority. It also deemed that edibles and beverages would only be available to medical marijuana patients and not casual consumers. Despite having $1 billion in cannabis sales potential by 2024, Mexico may be far less friendly to investors than they realize.

The facade of the New York Stock Exchange covered by a giant American flag, with the Wall St. street sign in the foreground.

Image source: Getty Images.

3. The first major U.S. exchange delisting for a pot stock

The tea leaves also appear to be on the wall that CannTrust Holdings (NYSE:CTST) will be the first marijuana stock on a major U.S. exchange to be delisted.

Although the New York Stock Exchange hasn't sent CannTrust a delisting notice, it's just a matter of time for two reasons. First of all, despite remaining highly liquid, CannTrust's share price has remained below the minimum listing price of $1 on the NYSE since Nov. 12. After 30 days, the NYSE is likely to send CannTrust a warning based on its low share price.

But the bigger issue here is that CannTrust hasn't filed its quarterly operating statements with U.S. or Canadian regulators since May 14. Not remaining compliant on financial filings tends to be a one-way ticket off major stock exchanges and back to the over-the-counter exchange. It looks unlikely that CannTrust will have its financial statements filed before sometime in the first quarter of 2020.

As a reminder, CannTrust was found to have grown marijuana in five unlicensed rooms at its flagship Niagara property for a period of six months (October 2018-March 2019). Aside from firing its now-former CEO, Peter Aceto, who was aware of the ongoing illicit grow operations, Health Canada wound up suspending CannTrust's cultivation and sales licenses. Though this does leave the door open for the company regain compliance, the fact that it's not able to plant any additional crops or sell cannabis makes delisting from the NYSE all the more likely.