Chemical substances that may cause severe side effects have been detected in eight counterfeit healthcare products, including weight-loss pills, the State Food and Drug Administration (SFDA) said Thursday.

Sibutramine, phenolphthalein and estazolam were among the chemicals found in the products, the SFDA said in a statement.

Studies show that sibutramine and phenolphthalein may cause high blood pressure and breathing problems, as well as lead to severe cardiovascular disease. Diet pills containing sibutramine were banned in October 2010, according to two previous SFDA announcements.

Estazolam, a prescription drug used only for the short-term treatment of insomnia, is said to cause dependence, dizziness, drowsiness and coordination problems.

The SFDA said the counterfeit products were detected through random sampling conducted in drug stores nationwide and were largely manufactured by companies in south China's city of Guangzhou.

The SFDA vowed to hand down severe punishments for the companies and will refer those that may have committed crimes to law enforcement bodies, the statement said.