A pizzeria has issued an apology to customers after accidentally getting them high.

Dozens of pizzas had been contaminated with THC after a chef mistakenly used cannabis oil to make a batch of dough.

Health officials warned pizzas bought from Famous Yeti's Pizza in Wisconsin between Tuesday and Thursday could have been accidentally contaminated with the drug after five customers were helped by emergency services.

A statement from the restaurant, posted to social media, said: "We sincerely apologize for any inconvenience or harm caused."

Responders from Stoughton Fire and EMS initially thought the symptoms could have been caused by carbon monoxide exposure.

But a patient admitted to hospital told the health department described the feeling as being "similar to eating a THC edible".

They were then tested for THC, and the results came back positive.

Public Health Madison & Dane County said a staff member at the pizza restaurant ran out of oil and used a jug from the shared kitchen, according to the health department.

The employee did not notice a label on the cap that said the oil contained Delta-9 cannabis, which was derived from legal hemp, and they used it to make a batch of pizza dough.

Sanitation officers inspected the restaurant with Stoughton Police. A police officer tested a container that contained the oil and it was positive for THC.

Cale Ryan, the owner of Famous Yeti's Pizza, said the incorrect oil had been "mistakenly used from a cooperative commercial kitchen to prepare a batch of dough."

He added that from Oct 22-24: "Sixty contaminated pizzas were unknowingly served. The commercial kitchen supports multiple small food entrepreneurs, including a business that creates products containing Delta-9."

Symptoms caused by ingesting THC include dizziness, increased blood pressure, vomiting, nausea, anxiety and hallucinations.

"We don't know the dosage in the pizza and so reactions for some could be quite strong or unpleasant", the local health department said.

Stoughton Police Chief Dan Jenks told Wisconsin Public Radio that the investigation was ongoing but there "doesn't appear to be any malfeasance or anything criminal at this point."

"We want to be sure anyone who has this pizza on hand throws it away so they don't get sick," said Bonnie Armstrong, director of environmental health at Public Health Madison & Dane County.

"If you ate the pizza and are experiencing THC-related symptoms, please contact your health care provider or call 911 if your symptoms worsen."