ObjectiveProstate cancer can significantly impact mental wellbeing, creating uncertainty and morbidity. This study described patterns of psychotropic medication and mental health service use, as a proxy measure for mental health problems, 5 years before and 5 years after prostate cancer diagnosis.MethodsPopulation‐based registry data were linked with Pharmaceutical Benefits Scheme and Medicare Benefits Schedule data for all prostate cancer patients diagnosed in South Australia between 2012 and 2020 (n = 13,693). We estimated the proportion and rates of psychotropic medication and mental health service use before and after diagnosis. Multivariable adjusted interrupted time series analyses (ITSA) were conducted to uncover temporal patterns.ResultsFifteen percent of men commenced psychotropic medications and 6.4% sought out mental health services for the first time after diagnosis. Psychotropic medication use rose from 34.5% 5 years before to 40.3% 5 years after diagnosis, including an increase in use of antidepressants (from 20.7% to 26.0%) and anxiolytics (from 11.3% to 12.8%). Mental health service use increased from 10.2% to 12.1%, with the increase mostly being general practice mental health visits (from 7.8% to 10.6%). Multivariable ITSA indicated a significant rise in medication and service utilisation immediately before and in the first 2 years following prostate cancer diagnosis.ConclusionThere is a clear increase in psychotropic medication use and mental health service use around the time of prostate cancer diagnosis. Mental health outcomes of men with prostate cancer may be improved with early mental health screening, particularly during the diagnosis process, to enable early intervention.