A Dundee business said it will be “remaining vigilant” after the discovery of empty nitrous oxide cylinders near its premises.
A member of the public found the silver canisters near parking bays at the Riverside Inn on Riverside Drive.
The Evening Telegraph found a further four on a visit to the area, close to Dundee Airport.
Nitrous oxide is a colourless anaesthetic used as pain relief during dentistry and childbirth, and has become a popular “legal high” commonly known as laughing gas or hippy crack.
According to National Drugs Helpline Frank, it is considered a psychoactive substance which is illegal to produce or supply.
It is inhaled through a canister or balloon and creates a temporary sense of euphoria and calmness, as well as fits of giggling.
But it can also cause dizziness, paranoia and in some cases cause the user to faint.
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There is limited evidence to suggest people can get addicted to laughing gas, but there is anecdotal evidence of people reporting cravings for the substance.
A spokeswoman for the Riverside Inn said the venue operates a zero tolerance policy towards “illicit activity” while stressing there was nothing to indicate staff or customers from the restaurant were involved in any way.
She said: “We have a zero tolerance policy for illicit activity of any kind on our premises and our team will remain vigilant to spot and put a stop to anti-social behaviour.
“The car park is accessible to the public 24 hours a day and we have no reason to believe this isolated activity was carried out by guests in our pub.
The customer who discovered the items said he was “alarmed” by the find.
He said: “I noticed the items were within the car park. I thought initially someone had just dumped food rubbish out of a car.
“When I saw the cylinders I noticed they looked an awful lot like hippy crack.”
He added: “I’ve heard a lot of celebrities have been getting slated for inhaling this stuff out of balloons in the national press in the last couple of months.
“Reading up about them I realise like any other drug people can become addicted to it.”