GrabCar drivers are warned that drug dealers are increasingly using their services to make deliveries to clients, and they will be held liable if caught.
Narcotics Control Board deputy secretary-general Pol Col Suriya Singhakamol issued the warning on Friday.
He said drug traffickers were abusing GrabCar services to make deliveries, and the tactic could mean trouble for the drivers.
Even if innocent recipients of parcels hiding drugs, they could be charged.
"The senders will be held responsible for trafficking drugs, and the recipients with drug possession," Pol Col Suriya said.
GrabCar drivers could be arrested and prosecuted if found in possession of parcels containing illegal drugs.
Drivers should quickly inform police about any suspicious parcels, to prove their innocence. People who receive parcels they were not expecting should do the same, he advised.