Chinese officials have told pharmaceutical firms to check their suppliers after claims that some have used "gutter oil" to make antibiotics, state-run media report.
Officials are looking into firms that reportedly use the cheaper gutter oil rather than the more expensive soy bean oil in the production process.
Gutter oil is reprocessed kitchen waste dredged from restaurant drains.
It has been part of a series of recent food safety scandals in China.
The government said it would release its findings soon, without giving further details.
It is not clear whether these antibiotics pose a risk to public health, but the incident highlights how some firms cut corners to pursue profits, says the BBC's Martin Patience in Beijing.
Scandals over contaminated food - most recently gutter oil - have caused considerable public alarm in China in recent years.
In April, state-run media reported on how officials cracked down on underground workshops that used decomposing animal fat and organs to produce gutter oil.
Police said that most of the oil was sold to oil manufacturers for food production and making hotpot soup in restaurants.
In September last year, police arrested 32 people in an operation to prevent the sale of gutter oil as cooking oil.
More than 100 tonnes of oil produced by six underground factories were seized in raids across 14 provinces.
The raids took place following a four-month police inquiry.
In 2008, at least six babies died and another 300,000 were made ill by drinking infant formula tainted with the chemical melamine.