Antidepressants have been heralded as miracle drugs that have changed the lives of millions of people. Depression, we are told, is an illness – a disease of the brain that can be cured by medication. But what exactly is the evidence for this? Could it be that we've been misled?

According to drug companies, more than 80% of depressed patients can be treated successfully. Claims like this have made antidepressants such as Prozac among the most widely prescribed drugs in the world, with sales that top US$12 billion a year in the United States alone.

The companies claim that the effectiveness of antidepressants has been proven in published clinical trials showing that the drugs are significantly better than placebos.

But a closer look at the data tells a different story. Many depressed patients improve when given medication, but so do many given a placebo. The difference between the drug response and the placebo response is not all that great.