The fastest-growing nicotine product in the U.S. has been increasingly hard to come by — and some customers aren’t happy.

A shortage of Zyn, a smokeless nicotine pouch that users tuck into their lips to get a buzz, has fueled a wave of social media outcry in recent weeks, amplified by a legal challenge that forced its parent company to halt online sales earlier this week.

Zyn has been around since 2014, but sales took off in the past year amid a wave of online creators (“Zynfluencers”) expressing their loyalty to the product alongside mentions from popular podcasters like Joe Rogan and the Nelk Boys.

The increased attention has helped fuel a sales boom: In April, Philip Morris, which acquired Zyn maker Swedish Match for $16 billion in 2022, reported shipments had soared 80% year over year to reach 131.6 million cans. Today, Zyn accounts for approximately 3 of every 4 purchases of oral smoke-free products, according to Tobacco Reporter, an industry publication.

In a statement, a Philip Morris spokesperson acknowledged that there was a “short-term inventory constraint” on Zyn that was “demand driven.”

“An increasing number of adult smokers are choosing Zyn as a better alternative than continued smoking,” the spokesperson said. “No regulatory or production issues have affected distribution.”

Online and in interviews with NBC News, Zyn users have voiced frustration with getting their hands on Zyn products.

“I’ve just kind of moved to another brand while they figure out the shortage problem, which isn’t ideal, but you know, it is the only thing you can do at this point,” said James Perkins, the CEO of a software startup and a Zyn user.

On TikTok, content creator Hayden Iverson called the shortage a “Zyndemic,” saying he would be rationing his Zyn cans. At the end of May, he said, he went to four different stores near his home in Boca Raton, Florida, but wasn’t able to find any of his preferred tins.

“They’ve always been easy to find, but now they’re a little bit harder to find,” he said in a phone interview.

Iverson’s video drew thousands of likes and hundreds of comments, many from people who said they’ve also encountered difficulty finding the product.

Some online Zyn fans have speculated about whether a March fire at a Swedish Match factory may have affected supply. At the time, a representative for the company reportedly told Swedish outlet Aftonbladet that there was not a risk of a shortage.

The Philip Morris spokesperson said Swedish Match, which directly manufactures Zyn, is currently making investments to expand and diversify U.S. production, including adding capacity at its Owensboro, Kentucky, facility.

The factory is also making process adjustments to increase production to help ensure consistent supply, which the spokesperson said would improve continuously over the next year.

And Philip Morris said it is working on constructing a new U.S. factory for Zyn production.

But users may still be waiting for some time before they feel improvements in availability. Earlier this month, Philip Morris CFO Emmanuel Babeau said supplies wouldn’t “be back to a normal situation” until the end of this year, according to Bloomberg News.

And while the company has said the vast majority of sales occur in stores, the recent announcement that it was halting shipments from the Zyn.com website in response to a subpoena from the District of Columbia has fueled further fears about how supplies could be affected.

Even as he awaits a resupply, Perkins said he remains loyal to the brand.

“Other brands are just very much trying to almost copy [Zyn] and hope for the best,” Perkins said. “A lot of them just don’t do a good job. The flavor is so intense that it’s just not pleasant in your mouth or the nicotine pouch itself is just poor quality.”