Two men were arrested by gardai on Monday evening after complaints were made about drug use on a Cork-bound train from Dublin.
A video has emerged showing a man snorting a substance on the 6pm Dublin to Cork service in full view of other passengers.
Other train users complained about the behaviour and gardai were notified about the incident.
An onlooker on the train from Heuston Station told CorkBeo that two men appeared to be "out of it" and were very "intimidating".
Upon arrival at Kent Station in Cork city, two men were arrested in connection with drug use and were brought to Mayfield Garda Station.
One man, 50s, was found to be in possession of a small amount of suspected cocaine and will face a court appearance at a later date.
The other man was released without charge.
A garda spokesperson said: "Two men were brought to Mayfield Garda Station for the purpose of a search after reports of drug use on a train at approximately 8.30pm.
"One man, 50s, was found to be in possession of a small quantity of suspected cocaine and will be dealt with by way of summons. The other man was released without charge. "
Irish Rail confirmed that passengers did inform authorities on the train of the drug use and they were able to notify gardai immediately.
A spokesperson added: "All Heuston to Cork services have Iarnród Éireann personnel on board, to whom customers can report any issues of concern, or which require security or Garda personnel to assist.
"Furthermore, we are currently introducing Customer Service Officers on all our Intercity routes. While the focus of personnel is of course Customer Service, again they are in a position to seek support from security or Gardaí where required."
