A Pakistani health official holds a bottle of toxic cough syrup at a hospital in Lahore.

A government official says authorities are investigating cough syrup believed to have killed 33 people in eastern Pakistan in the past three days.

Abdul Jabbar Shaheen said Saturday that 54 other people are being treated at hospitals in the city of Gujranwala who are also believed to have consumed the syrup. He said those involved are thought to be laborers or drug addicts who drank the syrup to get high.

Shaheen said chemical samples collected from the victims' stomachs contained dextromethorphan, a synthetic morphine derivative used in cough syrup that can have mind-altering effects if consumed in large quantities.

Shaheen said it is being investigated whether the people affected by the syrup in Gujranwala drank too much of it, or whether there was a problem with the medicine itself. -Sapa-AP