(Bloomberg) -- Shares of a traditional Chinese medicine maker plunged by the daily limit after the son of one of China’s richest men questioned the efficacy of its drug commonly used to treat mild cases of Covid-19 in China.

Shijiazhuang Yiling Pharmaceutical Co. fell by 10% in Shenzhen on Monday after Wang Sicong --  Dalian Wanda Group Co. Chairman Wang Jianlin’s son -- reposted a video late last week on Weibo that questioned whether the World Health Organization had ever recommended the firm’s drug as Covid-19 treatment. The city of Shanghai has been distributing the medicine to its residents as the financial hub battles the virus outbreak.

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The stock has gained over 260% since end-2019, mostly for its Lianhua Qingwen capsules which have been recognized by the Chinese government in various treatment plans to to reduce Covid symptoms such as fever and sore throat for mild cases. The World Health Organization hasn’t approved the use of the drug or recommended it for treating Covid.

A spokesperson for the company didn’t immediately respond to a WeChat request and a call for comment.

Other traditional Chinese medicine manufacturers also sank Monday. Dali Pharmaceutical Co. and China Meheco Co. fell at least 8% each, while KPC Pharmaceuticals Inc. was down as much as 7%.

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