Two passengers were 'doing lines of cocaine' off the table on a Dublin-Cork train, according to a complaint made to Irish Rail.
A 19-year-old woman also says a teenage boy threatened to hit her with a machete.
These complaints were lodged with Irish Rail between January of 2020 and June of this year, and relate to the Dublin-Cork railway line.
One person said two people were doing lines of cocaine off the table on the train.
A similar complaint says two passengers had a number of plastic bags and drugs on the table, and they were consuming them openly.
Some other reports involve drunken or threatening behaviour and harassment.
One 19-year-old girl says three teenage boys continuously threatened her and made inappropriate sexual comments.
She says one of them said he'd hit her head with a bottle and machete if she didn't talk to him.
Dermot O'Leary, from the National Bus and Rail Union (NBRU), says a dedicated transport police is needed in Ireland.
He said: "The assistance of a dedicated transport police would help.
"I think it's only a matter of time before something serious is going to happen, unfortunately - and that's one [thing] I don't want to be true."
Irish Rail says Dublin-Cork is the busiest inter-city route.
It says while these incidents are regretted, 26 complaints over 18 months indicate the vast majority of journeys occur without incident.