Police are trying to establish if a youth who needed hospital treatment was the victim of a “spiked” drink in Holbeach.
Emergency services were called to Boston Road South car park at about 9pm on Friday.
A Lincolnshire Police spokesman said: “It is an ongoing enquiry and we are awaiting the results of tests to determine if any illegal substances were involved or if it was only alcohol.”
Anyone with information should call 101, quoting incident number 497 of October 20.
• Lincolnshire Police is warning people about a scam involving letters that are threatening drivers with a “notice of intended prosecution” for speeding.
The letter appears to be from the Government but a police spokesman said: “We have our own individual department that sends out notices on headed paper.
“If you are in any doubt, always check the information contained within the letter to confirm it is genuine by ringing the named police force.”