Marijuana stocks weren't all that hot in the first half of 2017. The situation began to turn around for several leading marijuana stocks in the summer, though. What's the outlook for fall? Pretty good -- at least for some stocks.

Canopy Growth Corporation (NASDAQOTH:TWMJF), MedReleaf (NASDAQOTH:MEDFF), and GW Pharmaceuticals (NASDAQ:GWPH) especially appear to have solid potential for gains. Here's why these are three top marijuana stocks to buy this fall. 

Marijuana buds are scattered across a pile of U.S. currency of varying denominations.

Image source: Getty Images.

Canopy Growth

It's been a crazy kind of year for the largest Canadian medical marijuana supplier, Canopy Growth. The stock soared nearly 45% by mid-February and then took a nosedive. By early June, the stock was down 25% year to date. Canopy Growth heated up again in the summer, though, with shares up 25% for the year so far.

There are several good reasons to think Canopy Growth's latest run will sustain its momentum. In particular, the company's core market of providing medical marijuana in Canada is booming. Canopy Growth reported sales in the quarter ending June 30, 2017, of $15.9 million -- up 127% year over year and 8% from the previous quarter.

Canopy Growth also is in great position to benefit from international expansion. The company's wholly owned subsidiary Spektrum Cannabis GmbH is set to grow from Germany's legalization of medical marijuana earlier this year. Canopy has also announced two partnerships in recent weeks, one in Spain and another in Australia, that should enable the company to increases international sales further. 

Of course, the biggest news for Canopy Growth is the anticipated 2018 launch of the recreational-marijuana market in Canada. As the largest supplier for the medical-marijuana market in the country, Canopy should enjoy huge growth once the new market opens up.

MedReleaf

MedReleaf stock began trading publicly in May. For much of the period since then, shares have languished. Over the past four weeks, however, MedReleaf stock has soared more than 20%.

As the second largest medical-marijuana supplier in Canada in terms of revenue, MedReleaf stands to profit from several of the same factors as Canopy Growth. The company reported a 19% year-over-year increase in sales in the quarter ending June 30, 2017. Look for even better growth in the coming months as MedReleaf benefits from increased market share for its cannabis oil products.

Like Canopy Growth, MedReleaf is also well positioned internationally. The company's Australian partners hope to get a green light from regulators in the country to cultivate and sell medical marijuana. MedReleaf had its first export to Brazil in July. And the company's subsidiary MedReleaf Germany GmbH is moving along in the process to sell medical marijuana in Germany. 

MedReleaf claims one of the best cost structures among Canadian medical-marijuana suppliers and significant growing capacity. That could help the company tremendously once the recreational market opens in the country. 

GW Pharmaceuticals

We could have included other Canadian medical-marijuana providers on the list, but I think GW Pharmaceuticals deserves a spot. The U.K.-based company started off 2017 with a bang but subsequently gave up all of its gains. Better days could be ahead for this cannabinoid-focused biotech, though.

Marijuana buds in a test tube lying on its side and sealed with a cork.

Image source: Getty Images.

GW Pharma expects to complete its U.S. regulatory submission for cannabidiol Epidiolex for treating Dravet syndrome and Lennox-Gastaut syndrome in October. The company also anticipates submitting Epidiolex for European approval of the same indications in the fourth quarter of this year.

Based on results from late-stage clinical studies for Epidiolex, GW Pharma's chances for approval seem to be pretty good. Some investors have been concerned about potential drug-drug interactions between Epidiolex and other anti-epilepsy drugs, but the company doesn't think these issues will derail approval. In fact, GW Pharma CEO Justin Gover recently said that there's a possibility that the biotech will enjoy longer patent exclusivity for Epidiolex in part due to the interactions with one commonly used epilepsy drug.

If all goes well, GW Pharmaceuticals could launch Epidiolex in the latter part of 2018. There are plenty of remaining hurdles, but the stock could again prove to be a huge winner as it has been in recent years.

A fall fall?

I'd be remiss if I didn't point out that, while each of these stocks could enjoy significant gains, they could also experience dramatic drops. Canopy Growth and MedReleaf are priced to perfection. Any bump in the road with expansion of the marijuana market in Canada or with the German medical-marijuana market could cause both of these stocks to suffer.

GW Pharmaceuticals has the same challenges that any small biotech faces. The company not only must win regulatory approvals, but it also will have to secure reimbursement deals with payers and effectively market Epidiolex. There's no guarantee that a commercial launch will be as successful as expected. 

Canopy Growth, MedReleaf, and GW Pharmaceuticals are three of the top marijuana stocks to buy in the fall, in my view. But the possibility of a "fall fall" is real as well. As is often the case in investing, great opportunities for rewards come joined at the hip with great risks.

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