Detectives say nitrous oxide cylinders, commonly known as laughing gas, have been stolen from a Welsh hospital.
South Wales Police are appealing for information after 4ft cylinders were taken from Prince Charles Hospital in Merthyr .
It happened sometime between midnight and 6am on Sunday, May 12.
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Police say "a quantity" of the cylinders were taken, but has not revealed how many.
A spokesperson for the force said: "The cylinders are about 4ft tall and we believe a vehicle would have been used to remove them.
"We are warning the public not to buy or use these cylinders as they could be dangerous."
Nitrous oxide has various legitimate uses from dentistry to the food industry.
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Leading drug advice service Talk to Frank say people open the canister, transfer the gas into a container (usually a balloon), then inhale from the balloon.
Nitrous oxide slows down your brain and your body’s responses, and the effects of the drug varies depending on how much has been inhaled.
Taking nitrous oxide can give a user feelings of euphoria as well as fits of giggles and laughter – hence the nickname laughing gas.
The website Frank explains: "It is very dangerous to inhale nitrous oxide directly from the canister, and doing it in an enclosed space is also very dangerous.
"If you take too much nitrous oxide you risk falling unconscious and/or suffocating from the lack of oxygen. People have died this way.
"Other risks include dizziness, which might make you act carelessly or dangerously."
Anyone with information should call 101 or Crimestoppers on 0800 555 111 quoting occurrence 1900169487.
