Researchers from the Technische Universität Munich in Germany looked at 33 meta-analyses of 16 different drugs to treat psychiatric disorders (including schizophrenia, bipolar disorder, major depressive disorder, obsessive compulsive disorder, Alzheimer’s disorder and attention deficit hyperactivity disorder), and 94 meta-analyses of 48 drugs to treat medical diseases (including cardiovascular disease, hypertension, rheumatoid arthritis, chronic asthma, type 2 diabetes and hepatitis C). A meta-analysis is a ‘trial of trials’ where all properly conducted clinical trials of a particular treatment are studied to calculate the true benefits of that intervention.

The research team, led by Professor Stefan Leucht, compared the effect sizes of the different drugs. An effect size of 0.2 is considered significant but low, and an effect size of 0.8 or above is considered high.

Some general medicine drugs had very high effect sizes, for example an effect size of 1.39 for proton pump inhibitors to treat reflux oesophagitis (commonly known as acid reflux), and an effect size of 2.27 of interferon to treat hepatitis C. But many commonly used general medicine drugs, such as statins and aspirin to prevent cardiovascular disease and stroke, had small effect sizes (0.12 for aspirin for secondary prevention of cardiovascular events and 0.15 for statins for cardiovascular events).

Overall, the effect sizes for the psychiatric drugs were found to be in the same range as the general medicine drugs. For example, antidepressants used as ‘maintenance treatment’ to prevent patients having a relapse of major depressive disorder had an effect size of 0.64, and antipsychotics used to prevent relapse in schizophrenia had an effect size of 0.92.

Taking all diseases, the mean effect sizes were only of medium size for both psychiatric and general medicine drugs.

Professor Leucht said: “We believe our study puts the effectiveness of psychiatric drugs and general medical drugs into perspective. There is a deep mistrust of psychiatry, fostered by reports suggesting that the efficacy of psychiatric drugs is very small. Psychiatrists, patients, carers and the media are often unsettled by these findings, and some may think that psychiatric medication is not worth the bother.

He added: “There are reasons why people should be critical about psychiatric drug treatment, such as a lack of diagnostic tests, commercial conflict of interest, unclear mechanism of drug action and side-effects. But our study shows that the psychiatric drugs were not generally inferior to those used in other medical specialties, and the effectiveness of psychiatric drugs is supported by randomised controlled trials.”