DEA Administrator Michele Leonhart reported more than 150 arrests and the seizure of $20 million in cash and other assets since the operation began in January. She said agents had also confiscated thousands of packages of synthetic drugs.
"Many who manufacture, distribute and sell these dangerous synthetic drugs found out first hand today that DEA will target, find and prosecute those who have committed these crimes," Leonhart said.
Leonhart said the investigation is the second stage of a three-part operation dubbed Project Synergy. The DEA said more than 200 people were arrested during the first phase, which ran from December 2012 to June 2013.
A 2012 law made synthetic marijuana, stimulants and hallucinogens controlled dangerous substances. Synthetic marijuana is made by spraying natural herbs with synthetic psychoactive chemicals.
The synthetic drugs are often sold online under coded names -- incense for marijuana and bath salts and plant food for other drugs. The DEA says they are especially dangerous because the ingredients are unknown.