I wish to draw the reader's attention to our study, ‘Prevalence study of head shop drug usage in mental health’, published in this journal in February 2013. This is in light of recent publications focusing on the differential effects of cannabinoids on the development of psychosis, ^{Reference Di Forti, Marconi, Carra, Fraietta, Trotta and Bonomo1} including the use of synthetic cannabinoids and an increased risk of acute psychosis. ^{Reference Papanti, Schifano, Botteon, Bertossi, Mannix and Vidoni2}

Our work examines the prevalence of the use of ‘legal highs’ among mental health patients and the self-reported effects of legal highs on mental health. We identified a prevalence rate of legal high use at 13% (n=78), with over half of users reporting a deleterious effect on their mental state. This risk was particularly increased for those with a history of a psychotic disorder, with two-thirds of individuals with a diagnosis of schizophrenia or schizoaffective disorder reporting an exacerbation of psychosis. Although it was a self-report survey, its findings emphasise a particular risk for individuals with mental illness secondary to the use of legal highs, and to the best of our knowledge it remains the largest survey of its kind.

A recent systematic review which sought to examine, among other variables, subjective effects and the harmfulness of legal highs failed to identify our study. ^{Reference Baumeister, Tojo and Tracy3} This may be a consequence of our chosen title, which reflected the term commonly used for legal highs in 2012 in Ireland, namely head shop drugs (a moniker for shops which sold legal highs). This has evidently meant that our study findings are missing from systematic reviews ^{Reference Papanti, Schifano, Botteon, Bertossi, Mannix and Vidoni2,Reference Baumeister, Tojo and Tracy3} and even from commentaries relating to legal highs within this very journal. ^{Reference Bowden-Jones4,Reference Meacher5}

This letter is a valiant attempt to remind readers of our findings, and in the process highlight the risk to mental stability in a clinical population from the use of legal highs. We hope that in framing this letter in the context of legal highs, future research and systematic reviews in this field will now locate our article when searching for publications relating to legal highs, notwithstanding any future change in the descriptive term for these drugs to novel psychoactive substances!