Aim Cannabis is the most widely used illegal drug in Ireland. We sought to describe the changing pattern of cannabis use and cannabis related health harms.

Methods Data was collated from two national population surveys and three national treatment databases, focusing on people under 34 years.

Results Past month cannabis use among adolescents and young adults increased after 2011, coinciding with a decline in perceived risk of regular use. The prevalence estimate for cannabis dependence increased from 1.1% to 3.6% from 2011 to 2015. From 2008 to 2016, there were increases in the rates of cannabis related addiction treatment episodes among adolescents and among young adults of 40% and 168% respectively. Cannabis related admissions to general and psychiatric hospitals increased by 90% and 185% respectively.

Conclusion A concerted public health response is required to address escalating cannabis related health harms which have coincided with the arrival of more potent cannabis.