Story highlights 35 restaurants under investigation for using opium poppy seeds in their dishes

The unusual seasoning has been banned as a food additive since 2013

(CNN) Dozens of restaurants in China have been busted for serving noodles, hotpot, grilled fish and fried chicken seasoned with possibly addictive opium poppies.

The China Food and Drug Administration said in a statement this week that a total of 35 restaurants were under investigation and five of those had already been prosecuted.

The regulator said the poppy derivatives it detected included morphine and codeine and called on local authorities to step up their monitoring efforts. The additive has been banned since 2013.

Cooks sprinkling powdered poppy on their dishes isn't uncommon in China although it's unclear whether it can make a restaurant's food genuinely addictive.

In 2014, a noodle vendor was detained for 10 days after admitting adding powdered poppy plant to his dishes to keep customers coming back.

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