At least 16 people have died after drinking a cough syrup in Pakistan, forcing authorities to shut down three pharmacies and a medicine factory.

The victims, mostly drug addicts, died at various hospitals in Lahore between Friday and Sunday after taking the syrup, believed to be toxic, according to local police.

“Some of the victims were found dead in a graveyard where addicts used to take different kinds of drugs,” police chief Atif Zulfiqar told AFP. The drug abusers took the syrup to get high.

Six people remain seriously ill in hospital after drinking the medicine, sold under the brand name Tyno. One of the patients in critical condition died Monday.

Local pharmacies were the cough syrup was sold have been shut down and their owners arrested following the deaths while the syrup would be confiscated from all pharmacies and sent to a laboratory for investigation, health adviser for Punjab province Khawaja Salman Rafiq said.

This comes after 100 heart patients died in January after taking faulty medicines made locally.