WEST PALM BEACH -- A warehouse that exploded May 21 was home to a “very dangerous, large-scale” distribution center for synthetic marijuana run by three Palm Beach County men, federal authorities said Thursday.

Dylan Harrison, John Shealy and Michael Bryant also allegedly manufactured the drug — known by names such as “Mr. Nice Guy” — at warehouses in suburban West Palm Beach, according to a federal complaint. U.S. Drug Enforcement Administration agents raided two warehouses Wednesday.

The three men were arrested on charges including unlawful distribution of controlled substances. If convicted, they face up to 30 years in prison.

The arrests were among 90 made nationwide in the investigation, dubbed Operation Log Jam. The investigation — the first to target synthetic drugs — was prompted by local authorities around the country asking for help in battling synthetic marijuana. The product is easily accessible because quirks in the law allow it to be sold at gas stations, convenience stores and smoke shops as long as it does not contained banned materials.

Several cities in Broward and Miami-Dade counties have moved to ban the sale of such products.

In all, local and state law-enforcement agencies nationwide aided the DEA, the Internal Revenue Service and U.S. Customs and Border Protection in seizing more than 4.8 million packets of synthetic drugs, $36 million in cash and $6 million in assets. DEA Administrator Michele Leonhart told reporters in Arlington, Va., on Thursday that she had a message for those who distribute and manufacture synthetic marijuana: “You are nothing more than a drug trafficker and we will bring you to justice.”

Leonhart said use of the drug is a growing epidemic comparable to prescription pills, especially among young adults.

In 2010, poison centers nationwide recorded about 3,200 calls related to the synthetic drugs and bath salts. In 2011, those calls spiked to more than 13,000.The investigation into Harrison, 31 of West Palm Beach; Shealy, 39, of Royal Palm Beach, and Bryant, 29, of Delray Beach, was jump-started when Joel Lester, a 52-year-old Boca Raton businessman, was arrested in January on charges of distributing the drug as a product known as Mr. Nice Guy. After his arrest, Lester agreed to work with DEA agents in bringing down the men who sold him the synthetic product.

Leonhart mentioned the Georgia Avenue warehouse explosion Thursday as one of the more dangerous operations.

“It burned the place to the ground,” she said.

“Fortunately, our agents and task force officers and state and local folks were able to arrest those manufacturers yesterday.”