Four women were taken ill after visiting pubs and clubs in Bedfordshire in suspected drink-spiking incidents.
Police say they received four separate reports from women in Dunstable on Saturday night.
Sandra Evans, from Bedfordshire Police, said: “Our enquiries so far lead us to believe that in each case the women were victims of drink spiking, and we would urge anyone who has information that could help us to contact us immediately to help prevent further cases.
“We’re also reminding people never to leave their drinks unattended and to keep an eye on their friend’s drinks. Don’t accept drinks from a stranger and if you think a drink has been tampered with, dispose of it immediately.”