The woman who had a nitrous oxide canister signed by Simon Bridges says the National politician was "blissfully unaware" of what he was putting his name on to.
An image of the canister, known colloquially as a nang, appeared on social media on Thursday with the leader of the opposition's signature emblazoned across it.
The canister contains a colourless gas commonly used for sedation and pain relief.
In recent years, they have become popular to some as a form of altering the state of mind if the nitrous oxide is inhaled to produce a short-lived, dissociative high.
The gas can also cause a drop in blood pressure, fainting and heart attacks.
A picture of the signed nang was posted for sale to the Facebook page for Otago University's student magazine Critic Te-Arohi.
"NANG SIGNED BY SIMON BRIDGES," read the caption. "Serious inquiries only."
Another picture of the whipped cream canister was posted on Twitter by a woman who claims she told Bridges it was an urn.
"Got my nang signed by the blissfully unaware Simon Bridges," she wrote.
While nitrous oxide can be used as a drug, it is also used for baking. The gas is used to whip cream.
"Mr Bridges has a love of baking and supports anyone who takes this up as a profession or hobby," a spokesperson for the National MP told Newshub.
"Mr Bridges is sure that anyone who is in possession of one of these canisters has it for the right reasons."
A picture of Bridges baking a Mary Berry Log with his children was attached to the response.