A simple genetic blood test could offer hope to thousands of patients who suffer from depression that does not respond to medication, researchers have revealed.
Up to 40% of people with depression have a genetic abnormality that means they do not respond to treatment with antidepressants, the researchers at the Mayo Clinic Mood Disorders Unit in the US said.
Using a process called genotyping, the team found that a quarter of patients with a genetic abnormality produced a liver enzyme which either inhibited the effects of Prozac or caused unpleasant side-effects.
Professor David Mrazek of the Mayo Clinic said that one in 10 patients were poor at metabolising some common antidepressant medication including Prozac and Seroxat. "As a result, they may get adverse effects including nausea, headache, vomiting and sexual problems, from a regular or even low dose of the drug," he said.
So far, genotyping - which costs about £150 per gene tested - is not widely available in the UK. "The cost of the test may be a barrier to more frequent use of genotyping," Professor Mrazek said. "But it is now proven beyond doubt that in many cases, unpleasant side-effects can be avoided with this simple blood test."
The research was presented to the Royal College of Psychiatrists' Annual Meeting in London this week.