Officers in Crumlin in south Dublin are investigating the theft of the substance from the premises on the Walkinstown Road.
The burglary occurred at the veterinary surgery in Dublin 12 sometime last night.
During the burglary 8 x 100ml of Dolethal was taken.
The substance is veterinary medicine which is used by veterinary surgeons to administer euthanasia to animals.
This medicine is extremely dangerous and can be lethal if taken orally or injected by humans, authorities said.
Gardai in Crumlin are appealing for members of the public to come forward with information regarding the theft.
Possible witnesses are asked to notify Gardai if they have any information to contact them in Crumlin on 01 6666200, the Garda Confidential Line on 1800 666 111 or any Garda station.