Lahore: Nisar Ahmad Cheema, the Director General of Health of Punjab province, told reporters that dextromethorphan - an active ingredient imported from India - was found to be responsible for the cough syrup-related deaths in Lahore and Gujranwala districts.
Twenty people, most of them drug addicts, died in Lahore in November after drinking a cough syrup named Tyno.
Another 20 people died in Gujranwala and Toba Tek Singh districts in December.
The cough syrups linked to the deaths were made with dextromethorphan, officials said.
"Samples taken from victims in Lahore show a very high concentration - 4.1 mg/ml to 7.8 mg/ml - of dextromethorphan," Cheema said.
A concentration of 3 mg/ml is considered lethal, he said.
Pakistan Pharmaceutical Manufacturers Association vice-chairman Nasir Qureshi, however, described Cheema`s claim as "ridiculous", saying over 65 local and multinational pharmaceutical companies were using dextromethorphan in their cough syrups.
These medicines are available in abundance in markets across Pakistan, he said.
Qureshi said if Cheema`s claim is accepted, the cough syrups should have caused many more deaths than those reported so far.
Investigations into the deaths had revolved around the ingredient purchased by two pharmaceutical companies from India, he said.