Drug alert: The Department of Health urges people not to buy or use slimming product Xi Zhi Su, which can cause serious side effects.

The Department of Health urges people not to buy or use slimming product Xi Zhi Su which contains undeclared Western drug ingredients phenolphthalein and sibutramine which can cause serious side effects.

Phenolphthalein was once used for treating constipation but has been banned for its cancer-causing effect.

Sibutramine is a Western medicine used as an appetite suppressant. Its side effects include increased blood pressure and heart rate, psychosis and convulsions. People with heart problems should not take it.

Products with sibutramine must be registered before they can be sold in Hong Kong on a doctor's prescription and dispensed under a pharmacist's supervision.