Researchers in the US have found evidence that suggests the placebo effect is dependent on patient’s genes.
The placebo effect can be described as an improvement in health or behaviour not attributable to a medication or invasive treatment. An example of a placebo could be a sugar table given to a patient instead of one containing active ingredients. It has been a highly researched area and a medical mystery for over 70 years.
New research, published in PLoS ONE this week, shows how the extent of people's placebo responses may be explained by genetic differences that vary the amount of dopamine in their brains.
This was assessed using a gene called Catechol-O-Methyltransferase (COMT). A person can have a number of variants of the COMT gene; met/met, met/val or val/val. People with the met/met variant have four times more dopamine available in their prefrontal cortex (an area of the brain that is linked to cognition, personality expression, decision making, and social behaviour) than those with the val/val variant.
Paper author Dr Kathryn Hall, proposed that if dopamine is involved in the placebo effect, then a person’s COMT type would determine their response.
This proposal was tested by looking back at a 2008 clinical trial, which investigated the placebo effect in patients with irritable bowel syndrome (IBS). Hall and colleagues were then able to find patients genotypes from their blood samples.
They found that as the copies of met in the COMT gene increased, so did the placebo response ("presumably because more dopamine was available", says Hall). In some cases met/met carriers showed 6 times the improvement in symptoms than those val/val carriers.
Hall says their results suggest "met/met is a genetic marker for the placebo response and val/val is a marker for non-response".
"With this new research, we may now be able to use a person's genetic makeup to predict whether or not they will respond to a placebo,"
This has important implications for patient care, and will also help researchers design and carry out more cost-effective clinical drug trials.