The Opioid Receptor Mu 1 (OPRM1) rs1799971 and Catechol-O-methyltransferase (COMT) rs4680 as genetic markers for placebo analgesia

The placebo effect is considered the core example of mind–body interactions. However, individual differences produce large
placebo response variability in both healthy volunteers and patients. The placebo response in pain, placebo analgesia, may be
dependent on both the opioid system and the dopaminergic system. Previous studies suggest that genetic variability affects the
function of these 2 systems. The aim of this study was therefore to address the interaction between the single nucleotide
polymorphisms opioid receptor mu 1 (OPRM1) rs1799971 and catechol-O-methyltransferase (COMT) rs4680 on placebo
analgesia. Two hundred ninety-six healthy volunteers participated in a repeated-measures experimental design where thermal heat
pain stimuli were used as pain stimuli. Participants were randomized either to a placebo group receiving placebo cream together
with information that the cream would reduce pain, or to a natural history group receiving the same pain stimuli as the placebo group
without any application of cream or manipulation of expectation of pain levels. The results showed that the interaction between
OPRM1 rs1799971 and COMT rs4680 was significantly associated with the placebo analgesic response. Participants with OPRM1
Asn/Asn combined with COMT Met/Met and Val/Met reported significant pain relief after placebo administration, whereas those with
other combinations of the OPRM1 and [...]