Two south Chinese restaurants were found to be serving their food with poppy seed powder–which contains addictive substances like codeine and morphine–to ensure diners would come back for more.

Officials with the Food and Drug Administration (FDA) in Guangzhou Province checked 70 restaurants last year, and found that two were using marinade sachets containing poppy powder, Yangcheng Evening News reported.

Zhan Ke, who works for the Guangzhou FDA Restaurant Division, told the paper that heavily seasoned or aromatic sauces may contain poppy seeds. In their spot check, the inspectors targeted soup base, home-made chilli sauce, brine, and curry sauce.  Tests revealed several substances, that could damage the digestive and nervous systems, including codeine, morphine, papaverine, noscapine, and thebaine.

In 2012, inspectors in Jiangsu Province sampled over 400 hotpot soup bases, and found 10 percent contained poppy seed ingredients, according to a report by Oriental Daily earlier this year.  Also, many seasoning stores in Beijing sell poppy seeds and many noodle shops and barbeque stands were big buyers.