A Chinese restaurant owner has been arrested after allegedly lacing dishes with opium in an effort to keep customers coming back, BBC News reported.

The owner of the Yan’an noodle shop, known only as Zhang, admitted he bought 4.4 pounds of poppy buds in August. The buds contain the opium poppy seeds, from which the addictive narcotic opium is made. 

Zhang allegedly crushed the buds into powder form and mixed them into menu items.

Police discovered the secret ingredient after one of Zhang’s customers, Liu Juyou, 26, tested positive for drugs during a routine traffic stop.

Cops held Juyou for 15 days until he sent relatives to the restaurant to eat the noodles in question.  After the family members tested positive for drugs, police launched an investigation.

Zhang was arrested and detained for 10 days.

An anti-narcotics police agent told BBC News that chemicals from poppy can build up in the body and create a positive result on an opiate drug test.  Ingesting the food over a long period of time can even have an addictive effect.

Unprocessed poppy seeds used to be a popular ingredient in Chinese fare, but their use has since been banned, according to the BBC.

Click here for more from BBC News.