A survey by Xinhua News Agency showed that poppy capsules have been illegally used as a condiment in foods such as hot pot, noodles and crayfish in some restaurants to create repeating customers in several provinces, the agency reported on Thursday.

Xinhua found cases of poppy capsule usage in multiple regions including northwest China's Shaanxi province, southwest China's Sichuan province and Shanghai municipality.

Poppy capsules, a major source of many opiates, contain morphine and codeine and is prohibited for sale and use in food according to China's law.

Zhao Lan, a doctor at the Third People's Hospital of Chengdu in Sichuan, said long-term intake of poppy capsules will cause damage to the nervous system and can lead to an addiction that can cause chronic intoxication.

An unnamed cook with 10 years of experience in a hot pot restaurant in Sichuan province disclosed that poppy capsules have been a "secret recipe" for some small restaurants to lure customers. The capsules are publicly sold online and offline at prices as low as 400 yuan per kilogram (about $65 per kilogram).