Nearly 2,000 class A drugs have been stolen from a medical centre in Barnsley.
Thieves broke into the Brierley Medical centre in Church Drive on Tuesday night or Wednesday morning, police said.
Tranquilisers Temazepam and Diazepam were among the 1,928 stolen tablets and officers warned they could be dangerous if they fell into the wrong hands.
"The tablets could pose a serious risk, especially to children," a South Yorkshire Police spokesman said.
Anyone who finds the drugs dumped somewhere or is offered them under suspicious circumstances is asked to contact the police immediately.