Investing in public marijuana company stocks is hot, but the risks might leave many out in the cold.

Last year the sector experienced double-digit gains, indicating that marijuana is emerging as a legitimate investment opportunity. The Viridian Cannabis Stock Index of 75 publicly traded companies reported a 38.4 percent gain in 2014.

The trend prompted Founders Fund, the San Francisco-based venture capital firm run by PayPal co-founder Peter Thiel, to enter the fray in January. The company agreed to invest millions in Privateer Holdings, a private equity firm in Seattle that’s backing several private marijuana start-ups, including Tilray, a Canadian medicinal pot company, and Marley Natural, a weed purveyor launched by heirs of the late reggae star and ganja devotee.

Founders’ infusion prompted several other mainstream private investors to finally take stakes in that rapidly growing yet complex and still risky multibillion-dollar marketplace. The ArcView Group, a cannabis industry investment and research firm based in Oakland, California, predicts a 33 percent rise in marijuana sales this year, to $3.5 billion from $2.7 billion in 2014. And that’s just for legal weed alone. [Read more at CNBC.com]