Cannabis is the most widely used illicit drug and its use is associated with several adverse mental and physical health effects and negative social outcomes. Cannabis has the lowest initiation age of any drug, and earlier use increases risk of adverse effects and later use of hard drugs. Attitudes and perceived risk towards drugs are regarded as strong influences in determining cannabis use.

To investigate the attitudes of Irish adolescents towards the risks associated with cannabis use. To evaluate their awareness of its associations with adverse health and social outcomes.

This was a descriptive, cross-sectional study using a structured, anonymous questionnaire. The study was undertaken in nine public and private secondary schools in Cork City and suburbs. Students aged 15–18 were included.

39.3% of students (n = 199) reported previous cannabis use. There were significantly lower levels of perceived risk of cannabis among those who had used it compared with those who had not for all categories of social, mental and physical health risks (p < 0.01). There was a notable lack of awareness of a potential increased risk of schizophrenia with cannabis use. Frequent cannabis users were significantly less likely to report an association with anxiety, paranoia and schizophrenia. The great majority of teenagers (n = 382; 75.8%) believe that they are not given enough information about cannabis.

Teenage cannabis users perceive low risk associated with its use. Students are uncertain of its mental and other effects, and feel uninformed about its use.