Dozens of potentially lethal painkillers were stolen during a burglary in Dewsbury.
Thieves stole 100 Zo-morphine tablets and four packs of Tramadol from a house in Stoneyhurst Avenue overnight on Tuesday March 24.
The drugs can be prescribed to treat severe pain such as cancer or serious injuries.
Police are warning that the drugs could result in death or serious side effects if taken by people who have not built up a tolerance to them.
Det Insp Stef Wiseman, of Kirklees District CID, said: “We have sought expert opinion and the medical advice is that if these tablets are taken by someone who is not used to them or stronger doses are taken than recommended they can cause side effects such as vomiting, constipation, constricted pupils and gastric problems.
“There is potential that if they are taken by someone who has not built up tolerance levels or large amounts are taken that they could result in a fatality.”
The burglary happened between 7.55pm on Tuesday night and 1.05am yesterday (Wednesday).
Anyone with information about the medication or the burglary should contact police on 101 or CrimeStoppers anonymously on 0800 555 111.