The incident took place on the midnight of January 5 at a community guest house in Ahar town, situated on the banks of Ganga, SHO Ahar Surendra Singh Bhati said.
According to Bhati, around 150 persons were offered tea and biscuits as 'prasad' by three unidentified persons and they fell unconscious after consuming it.
The accused then looted their cash, cell phones and other belongings and fled away from the spot.
A case has been registered in this connection against three unidentified persons and two police teams have been formed to nab them, police said.