Vaping-related illnesses are killing the buzz for entrepreneurs who have been riding high on the marijuana legalization boom.

Sales of vaping products — the fastest-growing segment of the burgeoning pot market — are falling nationwide amid reports of hundreds of mysterious lung ailments — the vast majority of which have been linked to vaping THC, the main psychoactive compound in marijuana that gives the high sensation.

At Evergreen Organix, the largest producer of edibles, topicals and vapes in Nevada — owned by publicly traded Cannabis One — there’s been a “definite slowdown” in the demand for vaping products, Cannabis One CEO Jeff Mascio told The Post.

“I think it’s been a knee-jerk reaction, a little too extreme,” Mascio said of the response to the illnesses, which have resulted in eight deaths. “We’ve seen a negative trend against our vaping products since late August, but we’ve also seen our customers move to purchase more edibles and flower products.”

On Thursday, the FDA reported a total of 530 lung-related illnesses and eight deaths involving 150 different vaping brands. The agency also launched a criminal investigation focused on the supply chain and the ingredients going into e-cigarettes and THC vaping products.

Before the crisis, vaping pens, which are used to electronically heat marijuana oils or dry herbs, represented almost a quarter of all marijuana sales with a market share of 23.8 percent, according to data from Headset analytics, which tracks cannabis sales. That’s more than double this time two years ago, when vaping pens represented just 10 percent of the overall market, according to Headset’s vice president of marketing, Manny Perez.

Since the crisis, however, vaping pens have lost 4.2 percent of the cannabis market share in California over the six-week period through Sept. 9, Headset said. Their share of total sales are down 4.6 percent in Nevada, and 3.2 percent in Washington state, Headset said.

Sales of vaping cartridges, the cannabis oil pods used with vaping pens, also have suffered. In Massachusetts, for example, revenue from the sale of vaping cartridges at licensed dispensaries plunged 24 percent in a seven-day period ended Aug. 11, according to the Massachusetts Cannabis Control Commission.

Max Simon, the founder of Green Flower Media, the leading US educational and legal resource for the cannabis industry, worries the bad press could hamper the industry’s efforts to expand in other states, like New York and New Jersey.

The health crisis has people “very scared” of vaping and have “absolutely” affected vaping product sales, he said.

In Desert Hot Springs, Calif. — known as the “Starbucks of the cannabis world” for its loose regulations — the slowdown in vaping sales is the “talk of the town,” said Daniel Buelna, manager of Green Pearl Organics.

Buelna and others think the problem lies with knockoff vaping oils, which can often be found online and have been found to include products other than THC and cannabidiol, or CBD.

Still, proprietors insist overall sales remain steady as consumers switch from vaping to other products. “We believe the true impact on total sales will be negligible, and we don’t see it hurting our earnings or affecting our share price,” said Mascio of Cannabis One.

Shares of Cannabis One, which are not traded on a major exchange, fell 5.8 percent on Friday, to 25 cents a share.