Background: Psychotropic medicines are widely used to treat mental illness in the community. In prisons, however, the continuity and appropriateness of prescribing for mentally ill prisoners have been questioned. There has been little research on the use of psychotropic medicines in prisons in England and Wales; yet this information is essential for determining the extent to which there is equivalence of care between prisons and the community and for effective medicines management. Aims and objectives: This study aimed to determine patterns of psychotropic prescribing in prisons and consider the extent to which people with mental illness have 'equivalent' access to psychotropic medicines in prison.Methods: A mixed methods design was used, incorporating three interrelated studies: a retrospective case note review to estimate the proportion of prescriptions for psychotropic medicines which were discontinued on entry to prison; a cross-sectional survey to estimate point-prevalence psychotropic prescribing rates in prisons, as compared with the community; and a qualitative interview study with members of prison healthcare staff and patients with mental illness to a) explore the perceived purpose of psychotropic prescribing and b) to deconstruct patient and doctor accounts of medication changes on entry to prison.Findings: Half (47%) of all psychotropic medicines reported on entry into prison were not prescribed within seven days of arrival. The cross-sectional study found that psychotropic medications were prescribed to 20% of men and 44% of women in prison; age-adjusted prescribing rates were at least five times higher in prison than in the general population. However, no valid clinical indication was recorded for half (47%) of prescriptions for psychotropic medication in prison. Qualitative analysis showed that patients interpreted the principle of equivalence differently to doctors and attributed negative outcomes to changes to medication regimes in prison. Patients reported using psychotropic medicines to reduce symptoms of mental illness, but also as a coping strategy and to reduce insomnia. Whilst staff voiced concerns regarding possible overreliance on psychotropic drugs, patients perceived insufficient access to alternative forms of treatment and support in prison.Discussion: These findings confirm high use of psychotropic medicines in prison and caution prison prescribers against abrupt withdrawal of psychotropic medicines on entry to prison, overreliance on psychotropic medicines, potentially inappropriate prescribing and poor record keeping. Strengths and limitations, implications for practice and recommendations for future work are also discussed.