The market for cannabis has accelerated in a big way this year. And now investors can’t seem to get enough of marijuana stocks. It’s almost as if we are seeing a replay of the dot-com era.

So might there be a bubble brewing? Perhaps.

Bubbles can last awhile. In the case of the dot-com boom, it went from about 1995 to 2000. The move in marijuana stocks this year is based on some important events, though.

Just look at Constellation Brands (NYSE:STZ), which invested $3.8 billion in Canopy Growth (NYSE:CGC). There is also buzz that Coca-Cola (NYSE:KO) is looking at the space.

But despite all this, there should be some caution.

Pots stocks have already shown to be extremely volatile. Given this, here are some marijuana stocks to avoid:

Tilray (TLRY)

Among all the marijuana stocks, Tilray (NASDAQ:TLRY) is one of the higher quality operators.

The company has an experienced management team and there should be quite a bit of uptake with the legalization of cannabis for recreational purposes in Canada. Tilray also has been investing in new technologies with patent applications. In fact, the company is the first licensed producer of medical cannabis to have its facility receive the Good Manufacturing Practices (GMP) certification.

So then why stay away from TLRY?

Well, the primary reason is valuation. Since coming public in July, the shares have zoomed from $17 to a high of $300. True, the TLRY stock price has since come down to $151. Yet the market cap is still at a nosebleed $14 billion. This does seem like a fairly big stretch for a company that is forecasted to generate $40 million in revenues this year.

Besides, in light of the high valuation, it would be a good bet that there will be more capital raises, not to mention insider selling.

Cronos Group (CRON)

In the cannabis business, scale is important. It can mean snagging partnerships with large pharma and beverage companies. And of course, scale also can lead to more efficiencies and revenue potential.

This is why Cronos Group (NASDAQ:CRON) is at a disadvantage compared to other pot stocks. In terms of peak potential in the Canadian market, the company is around fifth or sixth place (or about 6,650 kilograms of cannabis per year).

Now the company is working hard to expand its capacity. Note that it is building an 850,000-square foot facility. But this will take time, and it won’t be cheap.

Finally, short seller Andrew Left — who operates Citron Research — has targeted CRON stock. Essentially, he thinks the company will have a very tough time competing in the market, especially since there are over 100 licensed producers in Canada.

Corbus Pharmaceuticals (CRBP)

Corbus Pharmaceuticals (NASDAQ:CRBP) is an early stage biotech company that is focused on synthetic cannabinoids. In other words, this does not require any planting and as a result, there can be more precision on the targeting.

For the most part, synthetic cannabinoids have shown signs of dealing with inflammation and other problems. Corbus has various clinical treatments, such as for cystic fibrosis and dermatomyositis.

While all this is great, there are still some issues with this pot stock. Besides the risks of getting approval with the FDA, which is never easy, the timeline could be a problem for investors. Keep in mind that the trials for cystic fibrosis will likely not end until the first half of 2020, which is a long time to wait. It could also mean there will be a need to raise more capital, as there remains a substantial cash burn.

General Cannabis (CANN)

General Cannabis (OTCMKTS:CANN) is a consulting firm that focuses primarily on the cannabis industry. Some of the services cover areas like on-site security, marketing and operations.

While such things are useful, it is not clear how big the market really is. What’s more, many of the services many be provided by other providers or be done in-house.

Consider that the latest quarter saw revenues of only $1.1 million, up 34% on a year-over-year basis. There was also a hefty net loss of $3.7 million.

All in all, this is really more of a startup … and yes, the $126 million market cap does seem fairly rich.

Cannabis Sativa (DBDS)

Cannabis Sativa (OTCMKTS:CBDS) develops and licenses cannabis formulas, edibles, topicals and other products. As for the brands, one is called “hi” (which has a pending trademark application on file). There is also a license for a lozenge delivery system as well as a patent for a strain of cannabis. CBDS even has a telemedicine service (which is a 51% owned unit called PrestoCorp).

But the company is still quite small. During the first six months of this year, revenues came to $301,064. As for the net loss, it was $2.2 million, compared to nearly $4 million in the prior year.

Unfortunately, the balance sheet is not in good shape either. Basically, for the company to continue as a going concern, it will need to raise more money.

But for now, investors do not seemed too concerned. After all, the market cap is still about $107 million.

Tom Taulli is the author of High-Profit IPO Strategies, All About Commodities and All About Short Selling. Follow him on Twitter at @ttaulli. As of this writing, he did not hold a position in any of the aforementioned securities.