Irish Rail received reports of the use of cocaine, ketamine and other drugs on trains last year.
They are among 277 anti-social behaviour complaints the company received in 2021.
Irish Rail got 258 complaints of anti-social behaviour in 2020 - rising to 277 last year.
One woman says she travelled on the Dublin to Cork train last November with her husband and young son.
She says there was a man sitting across from them taking cocaine for the entire journey.
Last September, a complaint was lodged about two men taking ketamine on the Dublin to Belfast route.
Several complaints also relate to drunken and aggressive behaviour, and people not wearing face-masks.
On the Belfast train, it is claimed a woman was 'intimidated' and 'preyed' upon by a group of drunk men.
On another train, there was a complaint of a drunken man threatening to punch and kill everyone on the train.
Dermot O'Leary, the general-secretary of the National Bus and Rail Union (NBRU), says dedicated transport police are needed to tackle the problem.
"The Gardaí are the best equipped in this country to police, we've always said that.
"And that's the route we've been pursuing for quite a while now.
"The Garda representative bodies themselves would be very supportive of that.
"Obviously they will need further resources from Government to do that - but it certainly would need a proper policing resort which'll have the powers of detention and arrest".
Irish Rail says it works extensively with other agencies, including the Gardaí, to combat anti-social behaviour.