LOUISVILLE, Ky. (WDRB) -- Synthetic marijuana was among the prohibited substances U.S. Customs officers say they discovered at the Louisville UPS express consignment operation.

Officers say the four shipments all originated from China, and were headed to various places across the U.S.  Besides the synthetic marijuana and a derivative of it, the substances included Afghan incense.

The amount seized could have produced 300 lbs. of synthetic marijuana. 

"Using synthetic marijuana is extremely dangerous," said Steven Artino, acting CBP director of field operations in Chicago. "You have no idea what you're ingesting."

Synthetic marijuana was originally produced for medical purposes. Its developers say its effects in humans haven't been studied yet and could be harmful. Side effects can include elevated heart rates, extreme paranoia, vomiting and hallucinations.