Paracetamol worth £30,000 was stolen from a lorry parked in a village near Barnsley while the driver was sleeping in the cab on Tuesday night (9 March).
Police said thieves targeted the HGV on Elmhurst Park in Dodworth between midnight and 5.30am and managed to steal the over-the-counter pharmaceuticals from the back of the vehicle.
Detectives are now appealing for anybody with information about the incident or the whereabouts of the Galpharm paracetamol to contact them.
Detective Inspector Tom Woodward said: “We are asking the public to be vigilant and aware of this incident. If you are suspicious of anybody selling these paracetamols in large quantities, please let us know immediately and do not buy them.
“The unique batch numbers, PYA0050A and PYA0051A, are written on the boxes.
“The remainder of these batches are set to be destroyed so that the only ones in circulation now will be the stolen ones.”
Woodward added: “The tablets are in big boxes which contain more than you could buy over the counter. If you are offered any for sale please let us know.”
Anybody with information about the incident should call the police on 101 quoting incident number 13 on 9 March.