A public information campaign is needed to ensure young people are better informed about the risks posed by cannabis, experts have said.

They made their comments after research they carried out found that in recent years, cannabis is "the dominant drug driving referrals to adolescent addiction treatment services".

Cannabis continues to be the most widely used illegal drug in Ireland, so doctors and researchers working in this field set out to assess the changing pattern of cannabis use and cannabis-related harm in recent years.

They looked at two national population surveys and three national treatment databases, focusing on people under the age of 34.

The study found that recent cannabis use by teenagers and young adults increased after 2011 and this coincided with a decline in the perceived risk of regular use.

This increase, along with the availability of higher potency "weed", has led to a big increase in the treatment of cannabis use disorders and cannabis-related hospital admissions.

For example, between 2008 and 2011, an average of seven people per 100,000 per year were subject to cannabis-related psychiatric hospital admissions. This doubled between 2011 and 2013 and since 2013, the average rate has been 17 per 100,000 per year - a 140% increase.

The rate of cannabis-related admissions to general hospitals increased three-fold between 2005 and 2017. The most common reasons for these admissions were epilepsy/convulsions, medication overdose and chest pain.

The researchers found that the rate of adolescent attendance at addiction treatment services peaked in 2014 and the rate of attendance by young adults peaked in 2015. In fact in 2015, an estimated one in 28 young adults were dependent on cannabis.

"In spite of this increased harm, there was a worrying increase in the proportion of young adults who saw little or no risk in regular cannabis use. This mismatch between a reduction in perceived risk and the growing scientific evidence that cannabis use is associated with multiple risks is a major concern from a public health perspective.

"It suggests that there has been a major failure to communicate risks to the general public. Alternatively, it seems possible that the very positive media coverage generated by campaigns, which are seeking to persuade politicians and the public that cannabis has substantial medicinal properties, are contributing to confusion among the public regarding its many known hazards," the researchers said.

They referred to research which shows that cannabis use appears to contribute to the development of psychosis and this risk increases if the drug is more potent.

"Adolescent cannabis use is associated with depression and suicidality in early adulthood. There is growing evidence that heavy cannabis use during adolescence has a negative impact on cognitive development and functioning," they said.

They warned that overall, these findings suggest "a concerning picture from a health perspective for Irish youth".

"A combination of displacement of low potency hash by higher potency "weed", a recent growing perception that cannabis is relatively safe and increased use appears to be driving harms upwards.

"There is a need for a public information campaign to ensure young people are better informed about the hazards posed by cannabis. Doctors have been reluctant to enter the cannabis debate in Ireland, as elsewhere, but given the evidence of escalating health harms, doctors should become more involved in these discussions," the researchers added.

The research was carried out by Dr Bobby Smyth who works in adolescent addiction services, Dr Anne O'Farrell of the HSE Health Intelligence Unit and Antoinette Day of the Health Research Board, and their findings are published in the Irish Medical Journal.