The State Food and Drug Administration has called for stricter enforcement of measures limiting the sale of cold medicines containing pseudoephedrine, which has been used for the illicit manufacture of the drug methamphetamine.

The Shandong provincial food and drug bureau has issued an emergency notice asking drugstores to keep a closer check on the identity of customers who buy the cold medicine Contac NT.

In March, 37 suspects were arrested in Liaocheng city for using Contac NT to produce methamphetamine, according to Liaocheng public security bureau spokesman Fu Yantao.

Fu told China Daily on Monday that the suspects bought nearly 1,000 packs of Contac NT Sustained Release Capsules to manufacture more than 60 grams of methamphetamine, known commonly as "meth", and also known by its street name "ice".

Ten packs of Contac NT, costing about 100 yuan ($16), can produce three grams of meth with a street price of 800 yuan, police said.

One of the main ingredients, pseudoephedrine hydrochloride, which eases nasal congestion, is converted into ephedrine to produce meth.

Contac NT contains 90 milligrams of pseudoephedrine hydrochloride per 95 milligram capsule, according to the website of GlaxoSmithKline China, the manufacturer of Contac NT.

Fang Fang, a manager at the publicity department of Glaxo China, told China Daily on Monday that the company is researching new ingredients for the Contac NT to replace the pseudoephedrine hydrochloride.

Fang said the amount of Contac NT sold on the Chinese mainland is a "sensitive issue" related to the pharmacy industry, and it's not the proper time to release the figure.

Under current regulations, customers can buy up to five packs of Contac NT at a time. The suspects asked relatives and friends to buy more, amassing nearly 1,000 packs, according to Liaocheng police.

Drugstores should record the information on the identification cards of Contac NT buyers, said Liaocheng police officer Wu Ying.

"The purchase of such medicines as Contac NT should be restricted," Wu said, adding they should be sold by prescription only.

In Jinan, capital of Shandong province, Haizhou Drugstore pharmacist Wang Ailing said customers can only buy one pack of Contac NT at a time. If they want to buy more than one pack, they have to provide their personal information to the drugstore. "Most recent customers are local residents. They know me and come in to buy a pack of Contac after catching a cold," Wang reported.

At the Zhang Zhongjing Pharmacy in the Jinshui district of Zhengzhou, capital of Central China's Henan province, customers can buy three packs of Contac NT, even with identification, said a store clerk.

Wang Huixian and Wang Ya'nan contributed to this story.