BACKGROUND: Over the last decade the use of psychotropic medications to treat common mental health problems has increased in Australia. This paper explores: 1) public attitudes towards the acceptability of using prescription drugs to treat depression and attention deficit hyperactivity disorder (ADHD), and 2) beliefs about over-diagnosis of depression and ADHD. METHOD: 1293 members of the general public were surveyed about their attitudes towards drug treatment for depression and ADHD through the Queensland Social Survey (QSS), an omnibus state-wide survey of households in the state of Queensland. The survey was administered through a CATI (computer-assisted telephone interviewing) system. Logistic regression analyses were used to predict belief that drug treatment is acceptable, and that depression and ADHD are over-diagnosed. RESULTS: Most participants (60.9%) said that it was acceptable to use prescription drugs to treat depression. In contrast, attitudes towards the use of prescription drugs to treat ADHD were much less positive with around the same proportion saying it was acceptable (42.1%) as unacceptable (38.2%). More than half of the sample agreed that too many people are diagnosed with depression when they don't really have it (57.7%), and 78.3% of participants agreed that too many children are diagnosed with ADHD when they don't really have it. Participants who said depression or ADHD were over-diagnosed were less likely to say that it is acceptable to treat these conditions with prescription drugs. CONCLUSIONS: Despite increases in prescribing rates there is still considerable scope for increasing the public's acceptance of treating common mental illnesses with psychotropic drugs. Furthermore, the public's views on over-diagnosis of depression and ADHD appear to reflect ongoing controversy about the proper identification of these conditions, and these views negatively impact attitudes towards drug treatment. This may be a barrier to effective treatment of these conditions given that drug treatment is often recommended as a first line response.