China's Ministry of Public Security China found the banned substance clenbuterol in veterinary drugs, the ministry said on its website on Sunday.

Jiangxi Hailian, a private enterprise in Haiyan county, Jiangxi province, that specializes in the production of veterinary drugs, sold clenbuterol-laced drugs in 21 provinces and municipalities.

Eight main suspects, including the company manager, who was identified only by his surname of Xiong, were arrested, and police seized more than 4,000 boxes with 20 kinds of counterfeit drugs. Six kinds of the counterfeit drugs contained clenbuterol.

The enterprise added the substance to the drugs to improve effectiveness and reap economic benefits, according to police.

The company, which claims on its website to sell veterinary drugs to farms all over the country, was unable to be reached on Sunday for comment.

China forbids the production, sale and use of clenbuterol, which makes pigs leaner, because residue of the chemical in livestock will cause health problems in humans, such as dizziness, headaches, hand tremors and palpitations, food safety experts said.

"Clenbuterol causes symptoms within several hours, and the greatest risks are to people with heart trouble," said Fan Zhihong, associate professor of nutrition and food safety at the China Agricultural University, who said a small amount of the substance would not be obvious but would be dangerous.

The case emerged when pigs from several farmers in Haiyan were found to contain the chemical in spot checks by the local agricultural economy bureau in February.

The technical director of the company, who the police only identified by his surname, Zhou, told police he found on the Internet that clenbuterol relieves asthma in pigs.

"We acquired the license number to produce veterinary drugs with qualified recipes and used it to produce substandard medicines," Zhou said, according to police.

The business got a certificate of Good Manufacturing Practices in 2005, which is required by drug manufacturers to produce veterinary drugs, and repassed the test last year, according to information from the Ministry of Agriculture.

The company used a warehouse behind a wall to hide the clenbuterol-laced drugs during inspections from authorities, Zou Yunfeng, a policeman who dealt with the case, was quoted by the Beijing News as saying.

"The managers of the business closed the door on a wall behind which the illegal drugs were stacked whenever drug inspectors arrived," he said. "They would mistakenly believe the warehouse behind the wall was outside the factory and didn't look into it."

Police have carried out campaigns against clenbuterol since it stirred widespread concern about pork safety when the Shuanghui Group, the country's largest meat processor, apologized in April 2011 for selling pork products that contained the additive.

In June 2011, police said 2.5 tons of clenbuterol had been seized in a nationwide crackdown in the previous six months and nearly 1,000 people were arrested on suspicion of manufacturing and selling the hazardous chemical.

zhouwenting@chinadaily.com.cn