Wu Yiling is one of China’s top scientists. With a fortune that neared $6 billion, he was also one of the world’s 500 richest people.

That was until last week, when the son of another Chinese billionaire sparked debate online with a post doubting the efficacy of Wu’s drug used to treat COVID-19. The herbal remedy, Lianhua Qingwen, is one of three traditional treatments the central government has recommended and was sent to households in Shanghai and Hong Kong during the latest omicron wave.

After a meteoric rise in Wu’s Shijiazhuang Yiling Pharmaceutical Co., the warning by Wang Sicong sent its shares tanking by the maximum 10% limit for two consecutive days. The slide then continued, taking the stock for its worst weekly plunge ever and down 35% from an April 11 peak. The wealth of Wu and his family has dropped $2 billion to below $4 billion, according to the Bloomberg Billionaires Index.