One man is due before court on a cocaine possession charge after passengers on the Dublin to Cork train alerted staff regarding the behaviour of two men on board.
The staff member reported it and gardaí were waiting for the men when they arrived at Kent Station.
A video taken by a passenger was circulated online which appeared to show one of the men snorting something off a table.
The incident occurred on the busy 6pm train from Dublin to Cork last Monday evening.
When the pair arrived at Kent Station that night they were met by officers.
They were taken to Mayfield Garda Station and subjected to a drugs search, during which a substance, suspected to be cocaine, was found.
One of the pair will appear in court at a later date, while the second was released without any charge.
A Garda statement said: “Two men were arrested and brought to Mayfield Garda Station for the purpose of a search after reports of drug use on a train on the 10th June 2019 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 said they took the matter very seriously.
“We were extremely concerned by the illegal drug taking on board the 18.00 Heuston to Cork service on Monday evening,” said a spokesman.
“Our employee on board was alerted by customers of this incident and reported it so that Gardaí were awaiting the arrival of the train in Kent Station.
“The two individuals were arrested upon arrival at Cork. Thankfully this is not a regular occurrence, and we commend the response of employee and Gardaí.”
Issues in relation to drug users travelling by train - from Cork, Galway, the Midlands and Belfast - to Dublin to purchase drugs has been highlighted before.
Last October a number of voluntary agencies in the Clondalkin area of west Dublin, backed up by local gardaí and Irish Rail, set up a harm reduction campaign aimed at those drug users.
The so-called Safe Campaign involved Clondalkin Alcohol and Drugs Task Force and local groups Tus Nua and the Clondalkin Addiction Support Programme.