Background In recent years, concerns have been highlighted in several jurisdictions, including Ireland, regarding abuse of over-the-counter codeine-containing medicines. On the 1st of August 2010, national regulatory guidelines aimed at limiting the supply of these medicines in Ireland came into force.

Aims To study the effects of the new regulations on the use of non-prescribed codeine-containing medicines by psychiatric patients admitted to an Irish university teaching hospital before (n = 117) the regulations came into effect and 6 months afterwards (n = 126).

Methods Participants completed a brief self-administered survey questionnaire about their use of over-the-counter codeine-containing medicines in the preceding 3 months.

Results Compared with before the introduction of the new regulations, there was a large decline in the reported ‘often’ or ‘regular’ use of codeine-containing medicines in the 3 months before admission (33.3% v. 17.4%, χ2 = 6.354, p = 0.01) and there was a reduction in the proportion of patients for whom others had expressed concerns about their frequency of use of such medications (15.5% v. 4.8%, χ2 = 7.29, p = 0.03). There was also a decline in the proportion of patients who stated that they would use codeine-containing medicines for either a ‘feel-good’ effect or to curb cravings (15.9% v. 1.9%, p < 0.01, two-tailed Fisher's exact test).

Conclusion We conclude that tight regulations on the supply of non-prescription codeine-containing medicines have the potential to reduce the use and abuse of such medicines in patient populations availing of admission to psychiatry hospitals.