A federal search warrant was executed Wednesday morning at a Main Street store in Keene.
Phat Stuff, at 84 Main St., sells smoking materials and adult videos and toys and has sold synthetic marijuana.
The U.S. Drug Enforcement Administration was assisted by Keene police.
The search warrant comes on the same day that the DEA served warrants across the country, as part of a national effort to crack down on the manufacture and sale of synthetic drugs.
Agents targeted manufacturers, wholesalers and retailers of synthetic drugs in 25 states beginning in the early morning Wednesday, according to the Associated Press.
A DEA spokesman could not be reached to find out if the Keene incident is related to the national crackdown.
A DEA agent left the store and briefly went to a vehicle parked in front of the store. He declined comment as he went back inside.
The city banned the sale of synthetic marijuana in local stores in summer of 2013. The drug is legally sold in N.H. stores as herbal incense.
Before the city ban, Phat Stuff was targeted by anti-synthetic drug activists, who claimed the store owner was knowingly selling synthetic substances to be used improperly.
A store employee told The Sentinel the store no longer carried the products in summer 2013.
Keene police Sgt. Jason Short stood inside the store's front door Wednesday, turning away would-be customers, as DEA agents could be seen through the windows, wrapping items up in paper.
"They wouldn't give me any information," said Matt Boardman, a sales associate at the store. "They're taking everything. They brought newspaper in to wrap all our glass. They said, 'We're shutting this place down, everything in here is ours.' "
Andrea, another sales associate at the store who declined to give her last name, said she and other staff members are very careful about following the law.
"We're very legal about everything," she said. "That's why I'm very confused about this."
Boardman, visibly upset, said anyone who looks younger than 35 years old has their identification checked as soon as they enter the store. Any customer who makes any reference to drug use while shopping in the store is denied service, he said.
The store opened on Main Street nearly three years ago, and operated in Winchester for about eight years before that.