Officers are appealing for witnesses and information following an altercation in St Albans last weekend.
On Saturday, March 5, police were called at around 11.15pm to report an assault.
It was alleged that a number of people became involved in a verbal altercation inside the Slug and Lettuce, Victoria Street.
This then turned into a physical altercation, and several people sustained injuries.
Two men were arrested on suspicion of assault at the time and later released.
No formal allegations of drink spiking were reported to police at the time.
Further information has since come to light regarding the altercation and officers are now appealing for further witnesses and information.
Detective Inspector Adrian Lysak said: “We are now working to build a full picture of the events that took place on the night. Initial enquiries have resulted in a lack of sufficient evidence, so we are now asking the public for their assistance.
“This incident took place in a busy bar, with a large number of people in attendance. We believe several people may have seen this incident unfolding, or witnessed the lead up to the altercation, and could have key information to help us progress this investigation. Please get in contact if you have any information.
“We take all reports of drink spiking seriously and would advise anyone who thinks they may have been spiked in any way to please report it at the earliest opportunity, so that as much evidence as possible can be gathered.”