Police seized 25 bottles of Phensidyl from the trunk of a fellow constable in Ishwardi, Pabna on Friday.
The arrestee, Md Naeem Hossain, is a constable of Pakshi Railway Police Station.
Pakshi Railway Superintendent of Police Shahab Uddin said the contrabands were in Naeem's possession while he was staying at Pakshi Railway Police barracks.
"He was sent to Pabna jail on Friday," Shahab Uddin added.
Several policemen from Ishwardi Railway Police Station said two drug dealers were arrested along with 264 bottles of Phensidyl in a raid on the Dhalar Char Express train from Rajshahi to Dhalarchar on Wednesday.
Another constable at the barrack saw Naim secretly removing bottles of Phensidyl from a police car and storing it in his trunk. He immediately informed Shahab Uddin, who directed the additional superintendent of police to investigate the incident.
Later on Thursday night, the Phensidyls were confiscated from Naeem's trunk.
However, the arrested constable claimed that he hid it in his own trunk on the instructions of Gopal Kumar Das, officer-in-charge of Pakshi Railway Police Station, and Ranjan Kumar Biswas, second officer of the same station.