After starting 2019 with a bang, many pot stocks took a breather in April. The two biggest marijuana-focused exchange-traded funds (ETFs) were down slightly last month. 

However, there were still several big winners in April. Neptune Wellness Solutions (NASDAQ:NEPT), 22nd Century Group (NYSEMKT:XXII), Constellation Brands (NYSE:STZ), Canopy Growth (NYSE:CGC), and HEXO (NYSE:HEXO) each gained at least 15% during the month. Here's what propelled these pot stocks higher -- and whether they're smart picks to buy now.

Five ascending stacks of coins with marijuana plants on top of each stack

Image source: Getty Images.

1. Neptune Wellness Solutions

Neptune Wellness Solutions focuses on the extraction, purification, and formulation of health and wellness products and has a licensed facility in Quebec for processing cannabis. And Neptune is on a roll, with its shares skyrocketing 27.4% in April.

The primary catalyst for Neptune last month was its announcement that it was entering the U.S. hemp market. On April 15, Neptune issued a press release stating that its solutions business segment had started to offer turnkey production development solutions with hemp-derived ingredients to U.S. customers. The company said that it had already established a supply chain in the U.S. with hemp extract producers and that initial orders were already flowing in.

2. 22nd Century Group

22nd Century Group is really more of a tobacco stock than a marijuana stock. The biotechnology company genetically engineers tobacco to contain very low levels of nicotine. But 22nd Century Group also has researched engineering cannabis plants to have low levels of THC. Regardless of how much of a marijuana stock you think 22nd Century Group is, there's no question that it's hot right now: Its share price soared 24.4% last month.

There were a couple of major developments for the company in April. 22nd Century Group announced early in the month that it had signed an agreement with KeyGene to develop hemp/cannabis plants with cannabinoid profiles tailored for medical and therapeutic use. At the end of April, the company reported that the FDA had completed an inspection of its manufacturing facility in North Carolina, a key step in the FDA's review process for 22nd Century Group's Pre-Market Tobacco application for its VLN brand low-nicotine cigarettes. 

3. Constellation Brands

You might not think of Constellation Brands as a pot stock, either. The company is best known for its premium beers such as Corona and Modelo. However, Constellation's $4 billion investment in Canopy Growth last year gave it a 38% stake in the Canadian marijuana producer -- and made Constellation a bona fide marijuana stock. It ranked as the No. 3 best-performing pot stock in April, with a gain of 19.2%.

The big news for Constellation last month were its solid fourth-quarter results. The company beat Wall Street's revenue and earnings estimates for the quarter. In addition, Constellation announced that it was selling its lower-performing wines and spirits business to E. & J. Gallo Winery for $1.7 billion.

4. Canopy Growth

Constellation Brands' cannabis partner, Canopy Growth, wasn't too far behind the big alcoholic beverage maker. Canopy's shares jumped 18.9% higher in April. But this performance had nothing to do with Constellation's positive Q4 results.

The main catalyst for Canopy Growth was its decision to buy the rights to acquire U.S.-based cannabis producer Acreage Holdings. Investors seemed to like Canopy's move to stake a claim in the U.S. marijuana market even though it can't actually acquire Acreage until marijuana is legal at the federal level in the U.S.

5. HEXO

Another Canadian marijuana producer, HEXO, landed the final spot on our list of the five best pot stocks in April. HEXO's share price was down more than 10% by the middle of the month but quickly turned things around to finish up 15.3%.

What sparked HEXO's big comeback? On April 17, Bank of America analyst Christopher Carey called HEXO a "top pick in cannabis." Carey also initiated coverage of the stock with a buy rating and a price target that represented a hefty 66% premium above HEXO's closing price on the previous day. 

Are they buys?

I think investors might be better off waiting and watching from the sidelines with a few of these hot marijuana stocks. Neptune and 22nd Century Group, for example, have intriguing growth prospects but are still quite speculative.

HEXO is a tougher call, in my view. The stock is more attractively valued than many of its peers. HEXO also has a strong market position in Quebec and a partnership with giant beermaker Molson Coors. However, the company still isn't a significant player on the international stage. I think that's where the major action will be soon. HEXO is tempting but my take is to hold off until it shows how it can compete effectively outside of Canada.

That leaves Constellation Brands and Canopy Growth. I like both stocks. Sure, Canopy Growth's valuation might be scary. The company is positioned well in Canada and in international markets, though. If the global cannabis market grows as much as many predict it will, Canopy will be a big winner.

And if Canopy is a big winner, Constellation will be one, too. I also like Constellation's move to sell some of its wine and spirits business. This frees the company to focus on more profitable efforts, especially its premium beers and the opportunity in cannabis.

I suspect that Canopy Growth and Constellation Brands will be two of the best marijuana stocks not just in the past month but over the coming decade.